Sunday, September 20, 2020

Some Planting Dont's

As we are moving into fall planting season it got me thinking back on some planting don’ts.  This was initially brought on by a sourwood tree that was planted here before we moved in.  Over seven years here it never got much bigger and for the past two years it was showing definite signs of decline.  I tried feeding it and acidifying the soil (it prefers a pH of 4.5-6) to no avail.  When it was finally dead this year I went to dig it out of the ground and found that I could lift it out of the soil with relatively little effort.  It turns out that even after over 7 years in the ground its roots never expanded outside the size of its original nursery container.  I suspect that the roots found it easier to stay within the original nursery mix rather than venture outward.  When I pulled it out of the ground there was very little soil left within the root ball.  Over the years the nursery mix broke down and dissolved away leaving nothing around the roots.

Here's my dead sourwood as it was
pulled out of the ground.


Sourwood trees usually produce deep lateral roots.  
Here the larger roots have circled back.  Also,
 there was little real soil within the root mass.


When planting a container grown plant you need to tease out some of the roots from the original container shape.  This is particularly important when dealing with a pot-bound plant.  In severe cases it may be necessary to cut the roots to encourage them to expand outward.  This was a case where it looked OK for a while.  Planting dos: the hole should be no deeper than needed so that its crown is just above the soil level.  The hole should be about twice as wide as original ball/container; and, back fill the hole with native soil, not more than half amendments, if any at all.  For compacted soils a wider hole is needed.  It also helps to make some jagged cuts to the sides of the hole rather than making it a smooth circle.  In this way when a growing root encounters the compacted soil interface it may be forced to penetrate it rather than just veering off to the side.  The goal is to get the roots growing outward and downward into the native soil-not to create a mirco-environment that the roots will never leave. Check out this link for more information on proper planting techniques.

Another thing to watch out for, especially in container grown plants, is circling roots.  These are thicker roots that reached the edge of the pot and curving around the edge of the pot.  Left uncorrected these roots will form a barrier to expansion of the trunk as the tree matures, eventually choking off the flow of sap up and sown the tree.  The best option is just not to buy a tree or shrub with circling roots.  If you already have one you can try to untangle the circling root, or it may be better just to cut it off for the long term health of the plant.

Sometimes the effect of poor soil contact is seen faster.  Because moisture moves from coarser to finer soils by capillary action, a container grown tree or shrub inserted into finer textured soils may dry out unless there is intimate contact between its roots and its new soil home.  This is because there is little tendency for soil moisture to migrate from the fine textured native soil to the coarser bark/peat moss/compost mix that the containerized plant comes in.  When planting container-grown plants I usually knock away a good portion of the planting mix to expose as many roots as possible and then put these roots in direct contact with the native soil.  I use the freed up planting mix as the ‘soil amendment’ to blend with the back fill.

 


The rounded crown of this once beautiful specimen has been
decimated to reduce problems with the power lines.  It's interesting that
the more upright trees (oaks, I think) located just a few feet back are not
interfering with the wires to the same degree.

Another factor that affects long-term plant survival is siting.  By this I don’t mean proper soil and light conditions, I am referring to location with respect to buildings and utilities, both above and below ground.  Planting big tree too close to a house can cause a multitude of problems ranging from root damage to the foundation and falling limbs to aesthetic problems like being out of scale with the house or blocking views.  Cultivars come in handy when working in a defined space.  These plants have predictable sizes and shapes thus reducing the effort to keep them the right size.  Utilities are another consideration.  You may get away with planting too close to them for a number of years, but when utility work needs to be done, your prized plants will be sacrificed for the sake of keeping the lights on or the water flowing.  Probably the most commonly encountered problem is planting large plants too close to overhead wires.  This conflict is often exasperated by the desire to have street trees and the first place we look to is the often too small strip between the sidewalk and street.  Utility companies publish guides and many communities have regulations about planting under utility wires [for example see this link from Baltimore Gas and Electric].  The general guidelines are to limit the mature size of trees and shrubs under wires to 25’ and not to plant larger materials within 25’ of the wires.  Larger plants should be located such that, when mature, their branches will not interfere with the overhead utilities.  Recommended plants will vary by region, but here in the Mid-Atlantic, good native candidates include Dogwoods, Redbuds and Hawthorns. 

This Bradford pear is starting to interfere with the power lines
and the lower branches on the street side have been damaged
by passing trucks.  This is just not a good location for a tree. 

Passing traffic is another factor to consider with street trees.  I had a Bradford pear planted too close to the road (planted by the city) that was repeatedly clipped by passing trucks and delivery vans.  It was also growing up into the power lines.  Perhaps the plan was that the Bradford would die or otherwise fall apart before it got to be much of a problem.  (Note that Bradford pears are proving to be invasive species as well as structurally unsound, and in my opinion are a very poor choice in any North American landscape)


The root flare is probably about 6" below the top of this volcano.  
An ideally planted tree would have no mulch within 3" 
of the root flare and the flare would be only an 
inch or two above the native soil level.

Mulch volcanos.  Fortunately these are showing up less often, but still many trees get this treatment.  Mulch mounded up and covering the root flare at the base of a tree will encourage bark rot and, more perversely, surface roots.  These are roots encouraged to grow in the loose, moist mulch, rather than deeper in the soil.  They are more susceptible to physical damage, can  dry out easily and many cases will circle and cross close to the tree truck.  As the tree matures, these crossing/circling roots choke off the main trunk from expanding outward, weakening the tree after 10 or 15 years of blissfully ignorant growth.


By putting a little extra thought into site planning and in helping plants get better rooted you can avoid a lot of disappointments in your long-term landscape investment.

Tuesday, August 25, 2020

Grasses are tough


Grasses are tough, not only do they grow just about everywhere, they can be very difficult to identify.  Unlike so many flowering forbs, grasses tend to all look about the same to the casual observer.  This situation is reinforced by our tendency to mow grasses down on a regular basis so that all we see are a collection of short green leaves.  In the US there are 169 genera and 1,398 species of grasses.  In the Northeast there are roughly 600 species growing in the wild.  Over the past couple of years I’ve making an effort to identify grasses growing on and around our property here in central Maryland.   

The first level of grass identification is to determine whether you are looking at a true grass (Poaceae) rather than a sedge (Cyperaceae) or rush (Juncacaeae).  You can make a quick distinction using the rhyme:  Sedges have edges, rushes are round, and grasses have knees (joints) and bend to the ground.  Sedges have triangular stems; when observed end-on the leaves will project out 120 deg apart.  The stems of rushes are round.  The stems of grasses have joints or knobs where each leaf blade originates.  In addition grass stems are hollow while those of sedges and rushes are solid.

While there are a few grasses that can be identified with some reliability on sight, most require close examination of the flowers and leaf surfaces with a hand lens to determine the grass down to the species.  Some easily identifiable species include the very popular little bluestem, Schizachyrium scoparium, and invasive species like Japanese stiltgrass, Microstegium vimineum, and Johnson grass, Sorghum halpense.  But for the most part you need to do a close examination to really determine a grass down to the species level.  There are a number of dichotomous keys for grass identification down to the species level.  Some rely heavily on flower (spikelet) characteristics, while others include other characteristics.  These keys ask a sequence of yes-no questions about the plants to slowly lead you to a result that matches the characteristics of the plant in question. 


Little bluestem is particularly recognizable in fall when the stems turn bronze
and the fuzzy seeds catch the light.  In summer the stems have a bluish green cast.


Johnson grass is a non-native weedy species that is often seen
 on the edges of fields and drainage areas.  It is tall 3-7'
and kind of looks like skinny corn stalks.  


Japanese stiltgrass in an invasive grass species, particularly in the
eastern United States.  It can be distinguished by the silvery midrib
on the elliptical leaves and its lax habit with many joints along the stems.


The Native Plant Trust (formerly the New England Wildflower Society) has developed an on-line key called GoBotany that allows one to enter a variety of plant characteristics simultaneously and provide a best fit.  This is particularly useful if you are trying to do an identification at a time when no blooms are available.  The plants in this database include grasses, forbs and woody species, but are limited to those found in the New England states. 

 To do a grass identification you’ll need an identification key and a hand lens (10x).  A camera is also useful to document your observations.  Since I made a commitment to ID some of my grasses I’ve been gathering a few different resources.  The Manual of Vascular Plants of Northeastern United States and Adjacent Canada, by Gleason and Conquist is a very technical key (in small print) that, while challenging to use, does provide detailed descriptions of each species. Grasses an Identification Guide by Lauren Brown is easier to use and well illustrated.  It also includes some common sedges and rushes in addition to grass species.  Its drawback is that it describes only the more common grasses.  Both of these references contain species found in the northeastern quarter of the US.

One resource I haven’t used much (yet) is Manual of the Grasses of the United States by A. S. Hitchcock.  This two volume set describes all of the grasses found growing in the US.  It does include some illustrations which makes it somewhat friendlier than Gleason and Conquist.  I’ve been intimidated by the size of this collection (especially large considering this includes only grasses, no rushes or sedges).

Here in the Mid-Atlantic region an easier to use key is the Field Guide to Grasses of the Mid-Atlantic by Sarah Chamberlain.  This guide includes botanical sketches of plants, and plant parts, to aid in the identification and includes only true grasses that are found in the Mid-Atlantic States (VA to PA).  So you don’t wade through extra species that are not likely to be present.  It includes many more grass species than Lauren Brown’s book, though it lacks the sedges and rushes. 

An additional book that I have found critically useful in all plant identifications is Plant Identification Terminology by Harris and Harris.  It provides illustrations and definitions of all the plant parts that are described in botanical Latin terms in the keys. 

Going through a dichotomous key can be time consuming, especially early on as you are wrestling with botanical Latin.  A drawback of many keys is that it is difficult to go backwards when you get something wrong, i.e., you get to the end of the key and your sample is nothing like the choices in the key.  Some of the more formal keys are easier to back up on when each step is numbered.  I’ve found with some of the book formats that they do not number the steps (choices) so that going backwards involves leafing through a lot of pages.  Perhaps putting some sort of bookmarks, like post-its, in the book would make it easier to retrace my steps. 

When I do go through a key and end up without a match I will go back to a point where I was not absolutely certain about my choice and then run down that new path.  Sometimes you just don’t have a good example of the feature that they are asking about; like size or shape of a seed, the number of veins on a lemma, or a surface is slightly or very hairy. 


Here you can see the individual florets of switchgrass.  This species has
only one floret per spikelet. Highlighted here are the glumes,
bracts that enclose the floret(s).  One of the florets is in full bloom
 with the anthers and stigma projecting out of the floret.

After getting frustrated about not getting satisfactory results I found it helpful to practice on some known species.  That way you can get some confidence with identifying botanical structures.  I had examples of switchgrass, Panicum virgatum, and purple top, Tridens flavus, that I could practice on.  After that I worked on an unknown grass that was a little past bloom, the flowers were a little tattered but mostly recognizable.  I found that one of my problems is counting florets in dried flowers.  Sometimes they just look like a bunch of chaff.  With a little practice I’m getting better at recognizing the flower parts.  I was able to ID the unknown as the relatively common, though non-native, smooth brome, Bromus intermis.

Here's the flower stalk for purple top.  The spikelets, which contain
4-9 florets, are deep purple in color.  Hence the common name.

One thing that surprised me in keying out grasses is that plants that are close together in a key may not look that much alike when viewed at a distance.  That is because many keys focus in on differences that are not easily seen rather than on obvious features like height or size of leaf blades.  While not part of some keys, knowing things like bloom season or habitat can be very useful in confirming an identification. 

In addition to running through keys, working with people who are familiar with grasses can be of great help.  For many, once you know and recognize a plant you don’t need to run through a key to identify it, they just know.  In this time of COVID-19 it is even more difficult to find and work closely with a grass expert.  I did recently find a Facebook group focused on identifying grasses called Grasses,Sedges and Rushes of the Northeastern USA.  They have been helpful in pointing me in the right direction when I have been adrift. 

The American mannagrass grows vigorously in early spring
 and is in full bloom by the end of June.

This was the case when I thought I had ID’ed a grass as drooping woodreed, Cinna latifolia.  This was thrown in doubt when I saw that the grass was going dormant in mid-summer while Cinna normally blooms in mid-summer.  Based on a lead I got from the Facebook group, I redid the ID using a different key and came up with American mannagrass, Glyceria grandis.  On reviewing the keys it appeared that I had totally messed up characterizing the flower (spikelet) parts by overlooking some of the less developed florets.  On a side note, it was interesting to see that areas that were thick with mannagrass had very little Japanese stiltgrass filling in in late summer.

 

Friday, July 31, 2020

July 2020 What to do about Japanese Stiltgrass NOW


In late July through early August Japanese stiltgrass, Mircostegium vimineum, puts on a major growth spurt prior to blooming.  This presents an opportunity for removing a large amount of this invasive annual grass before it blooms and begins to set seed for the following years.  There are several methods that can be used now, which is best depends on the particular situation. 

 

Pulling  This is my method of choice in areas of mixed species. In late summer stiltgrass can grow to 3-4 feet tall.  At that height it is above many desirable plants and you don’t need to bend over too far to pull it out.  By using a loose grip and grabbing higher up on the plant mass I can selectively pull out the stiltgass and leave most perennial and more deeply rooted plants in place. By wiggling the grass side to side as I’m pulling the relatively weak roots are broken and the stems remain intact.  

Here stiltgrass and the native grass nimblewill, Muhlenbergia schreberi, are growing together.

Pulling the stiltgrass with a light touch leaves the well rooted nimblewill in place.

I usually leave the piles of stiltgrass to dry out in the sun for a couple of days before disposing of it.  If the grass is not setting seed I’ll put it in a brush pile or in a segregated location where it can break down but will not accidentally be spread elsewhere.  If the grass has bloomed it will need to be bagged or put into an isolated location where the seed cannot escape.  This is the number one reason for pulling before bloom!

This is a woodland area where I have been pulling stiltgrass of 2-3 years. 
Though it looks dense there are not that many individual plants.

 

After 20 minutes of pulling I was able to clear this area of stiltgrass. 
What remains is a ground cover of mostly rosy sedge, Carex rosea.


Low Mowing  Mowing as close to the ground as possible in late summer (just before bloom) is a common recommendation for combating stiltgrass.  This prevents blooming and seed set in the upper stems.  Unfortunately stiltgass will also set seed in the stem at the base of the plant, 1-2 inches above ground level.  These cleistigamous flowers are difficult to remove without cutting really close to the ground.   If you wait too long to mow, after seeds begin to develop, mowing may only serve to spread seed unless you have a well fitting grass catcher on your mower.  ( In that case you should dispose to the clippings in a way that the seed will not escape into the environment.)  These extra flowers make stiltgrass very difficult to remove from turf areas.

Late summer mowing had been used in this area for 2-3 years.  Here it is in 2017. 
There is a lower density of stiltgrass, but still a lot.

I’ve been trying to remove stiltgrass solely by timed mowing in one area but have made only minor progress over 3-4 years.  What I have found to be most effective in lawns is to use a pre-emergent herbicide, marketed for crabgrass, in early spring.

Here is the area in 2020.  In addition to late mowing I treated this area with the
preemergent herbicide Dimension.  Above the line has been treated for
two consecutive years, below the line only once in spring 2020.

 

Weed whacking  Using a weed whacker can be effective where you can selectively cut down to ground level to remove those stem flowers. It can get tedious if you are trying to preserve desirable plants intermixed with stiltgrass.  You can leave the cut stems in place if the grass has not begun to bloom, but if it has you should consider raking out the debris.  (If plants are beginning to set seed weed whacking will likely spread more seed than doing nothing.)

I had good success in a woodland edge area using this method.  Starting out, the area was nearly a monoculture of stiltgrass so I did not have to be too careful.  In the second and third years I also raked out the cut stems.  I have also seeded the area with Virginia wild rye, Elymus virginicus, a shade tolerant native grass.  Now six years later I can manage that area with just a little pulling. 

 

Fire  Because stiltgrass is a weakly rooted annual burning at ground level can be an effective means for killing it.  I have been experimenting with burning stiltgrass at various times during the year.  Burning in early and mid spring reduces the amount of stiltgrass seedlings but does not eliminate its presence.  This is in part due to the extended time over which stiltgrass can germinate in the spring.  Burning in late spring seems to thin out the amount of stiltgrass but can also reduce the amount of desirable vegetation.  In one spot where I did a mid-spring burn the area was overgrown with stiltgrass by the end of July.  On removing that stiltgrass there were very few other plants growing there. 

This is a small area of lawn dense with stiltgrass that I burned with a garden torch
two days ago.  It's not necessary to consume the entire green plant with fire,
just burn the roots at the soil surface.  Perennial grasses should
bounce back in a week or two.


In this area I pulled most of the stiltgrass then used the torch to burn the surface
to kill any remaining vegetation.  I was then able to immediately plant several
plugs of switch grass, Panicum virgatum.


Where burning has proved very effective is in hard to reach areas where clear ground is desired, such as pathways and fencelines.  Burning stiltgrass is particularly effective in late summer. In lawns with cool season grasses you can burn areas infested with stiltgrass with a garden torch.  The cool season grasses are dormant because of the hot weather and dry conditions.  As the weather cools in September the clumps of cool season perennial grasses will resprout, without the presence of stiltgrass.

Here is the garden torch in action, burning the roots of some 3 foot tall stiltgrass. 
I can stick the torch through the openings in the fence the get to hard to reach areas.


It is interesting to note that heat is conducted better in slightly moist soil than in dry. While burning stiltgrass leaves no chemical residues you must use great caution to keep flames under control and not allow any fire to spread out of control.  There may also be local rules to follow.  


Herbicide   While I have had very good results from using preemergent herbicides in early spring to get stiltgrass out of the lawn, I have not had personal experience using postemergence herbicides to control Japanese stiltgrass.  Based on information provided by a number of university agricultural extensions there are several herbicides that can be used in summer time (up to the onset of flowering)  to control stiltgrass.  Low levels of the broad spectrum herbicide glyphosate, about half the normal concentration, are reported to be effective against Japanese stiltgrass.  Glufossinate is another broad spectrum herbicide that is effective against stiltgrass. 

I pulled this from the Rutgers Cooperative Extension (NJ) site:

Glyphosate and Glufossinate (various trade names) can be used to spot treat Japanese stiltgrass in gardens and planting beds. Both are broad spectrum herbicides that should be applied only to the unwanted plants. If applied to the foliage, stems, or woody portions of desirable plants, it could damage them as well.

Sethoxydim (tradename Bonide Grass Beater Over-the-Top Grass Killer®) and Fluazifop-P-Butyl (Ortho Grass B Gon Garden Grass Killer®) are selective herbicides that can be applied to growing stiltgrass in landscape beds. When used according to the label, these herbicides will not damage most non-grass ornamental plants. Be sure to follow the label closely and heed all precautions.

According to the labels on the Bionide and Ortho products these products are not effective on sedges.  That is a good feature for use in woodland edge habitats since native sedges are a major component of the ground covers growing there.  I not sure if that means that those, mostly desirable species would be unharmed, or, just not killed at a high rate.  I noticed that the label on the Bionide product indicated that it could be used safely on lawn with red and Chewings fescue.


Here is another example of the effectiveness of a preemergent herbicide. 
To the left of the line I applied dithiopyr (Dimension) in mid-March,
to the right is untreated.  


Sunday, July 5, 2020

Getting More Fruits

Sassafras blooms in the first part of spring. 
This photo was taken on April 12th.

I have been planting more native trees and shrubs with the goal of increasing the amount of food available for birds.  Particularly fruits that are available in fall and winter.  In many cases these plants are dioecious. That is, an individual plant of the species is either male or female.  To get berries you need at least one male to fertilize the female flowers.  Sometimes getting male and female plants is easier when you are buying cultivars.  It is often documented somewhere (but not always) if a cultivar is male or female.  When buying seed-grown natives it is difficult to tell unless they happen to be in bloom when you are shopping.  If plants are not in bloom the recommended approach is to get 5 random plants so that there will be a good chance that you will get at least one of each.

This year I have spotted some firsts in my campaign to produce more native berries.  The first success that I noted was that my newly planted sassafras tree, Sassafras albidum, was a female [note structure of female flower].  There is a number of wild sassafras in the area, but the flowers are way up in the tree so I have not been able to distinguish their gender.  About a month after blooming I noted that there were a couple of berries forming.  They are green right now, but will turn dark blue when ripe.
Female flowers have 6 sterile stamen (staminodia) surrounding
a central pistil.  Male flowers have 9 stamen.
Here at the beginning of July you can see the green berries.  When ripe these berries
will turn dark blue and the pedicels will turn red.


The second species I spotted with fruit forming was persimmon, Diospyros virginiana.  There has been male tree on the property for some time.  I don’t know if it’s wild or was planted by the previous owners.  When I moved 7 years ago I planted a number of native persimmons all of unknown gender.  To improve the chances that I had at least one female I planted 6 new plants.  Last year one of them bloomed that proved to be a male.  This year two additional trees bloomed, both of which were female.  Shortly after the flower petals fell off I noticed that two of the female flowers had swollen ovaries.  Now I can hope that they survive long enough to ripen.  I may need to build a little fence around them to keep the deer away.  
Female flowers are usually solitary and have 8 sterile anthers around the pistil.
 On male trees flowers are clustered and are typically packed with 16 anthers.

About a month later this persimmon is developing. 
Green now it will turn orange when it ripens in the fall.


Another recently planted native tree that is now showing some berries is fringe tree, Chionanthus virginicus.  Fortunately these bloomed the second year after planting.  The first three of these I planted either appeared to be females or had not bloomed after two years.  The following year in early June I was in a native plant nursery when these were in bloom.   I was able to identify one specimen as a male (paddle-shaped anthers in throat of flower) and bring it home for the girls.  Now 4 years later I’ve spotted the first berries on the fringe trees.  Like with the sassafras these start out green then turn dark blue when ripe. 
This green berry on the fringe tree will turn dark blue when it ripens in early fall.


Two years ago I replaced some invasive leatherleaf mahonia, Mahonia bealii, with some inkberries, Ilex glabra.  I wasn’t able to get a male cultivar locally.  I found a suggestion on the internet that other hollies could fertilize inkberries.  To try this I planted an early blooming winterberry holly, Ilex verticillata ‘Jim Dandy’ nearby.  After planting my collection of inkberries including the ‘Nigra’ and ‘Shamrock’ cultivars I took a close look at the flowers.  While the flowers on ‘Nigra’ were exclusively female, ‘Shamrock’ appeared to have both male and female flowers.  Unfortunately this year I forgot to take a close look at these flowers to confirm my earlier observations.  I can say that this year I am seeing a lot of berries developing on the ‘Nigra’ plants, as well as on a single wild-type plant.  The ‘Shamrock’ cultivars bloomed this year but are lacking berries.  They had a lot of berries in their first year here.  
This female flower has a large central ovary surrounded by six sterile stamen. 
In male flowers these stamen will have yellow pollen on the anthers.

Also on the holly front, this year I added another winterberry holly, ‘Winterred.’  This is a later blooming female.  Its blooming cycle is perfectly timed with the male, ‘Southern Gentleman.’  While it was still in its pot I placed the ‘Winterred’ next to the ‘Southern Gentleman’ until the blooming period was nearly completed.  This should ensure some berries as long as it doesn’t get stressed too much from being planted out in late June.

Some other species that are not dioecious have mechanisms that encourage cross pollination. This ranges from clever flower construction that prevents self-pollination, to offset timing of pollen release and receptivity, to outright rejection of pollen with the same genetic material as the ovary.  To encourage fruit and seed production you should have at least two genetically distinct individuals within pollination range. 

This is what I’m thinking about my single American plum, Prunus americana.   Despite several years of impressive blooming I have not seen any fruits on this tree.  I don’t know how long these need to mature before they are ready to bear fruit.  To help with cross pollination I’ve planted several bare root American plums in the area but I think it will be a few more years before these begin to bloom.

Another fruit-bearing native that has appeared on my property is black raspberry.  I’d like to think that these have been encouraged by the removal/reduction of invasives like Japanese stiltgrass, wineberry and garlic mustard.
Black raspberry has round stems and first year canes are glaucous. 
Flowering occurs in mid-May

The black fruits ripen around the end of June and have a distinctive sweet flavor. 
These ripen a week or two before the wild blackberries, which are much tarter.

Tuesday, June 9, 2020

Leaves of Three

Poison ivy has three leaflets, the center one has a longer stem.  Leaves have a central vein
with secondary veins branching off from it.  Young leaves are glossy, but older ones are variable
 and leaf margins are all over the place.
After a mild winter in the Mid-Atlantic, it's been a cool, damp spring.  This seems to have brought out a lot of growth in the understory.  Included in this lushness is plenty of poison ivy, Toxicodendron radicans, formerly, Rhus radicans.  As I have been doing some weeding I have been vigilant for ‘leaves of three’, the rhyme for identifying poison ivy.  But that is not the only plant out there that sports three leaflets. 

Following are some common plants that bare some resemblance to the dreaded poison ivy.  Probably the most common look alike in the Mid-Atlantic region is box elder, Acer negundo.  When I first encountered this tree I thought OMG it’s a  poison ivy tree!  This tree reseeds prolifically generating a myriad of seedlings with bright green leaves divided into three leaflets.  While superficially similar to poison ivy, on closer examination you can see that box elder has an opposite arrangement of leaves and branches, while those of poison ivy are alternate.
Box elder has three leaflets that appear very similar to
poison ivy, but branching is always opposite.  Leaf margins are variable
Here they are side-by-side.  Box elder seedling at top has opposite branching,
poison ivy in mid-frame is opposite.  The yellow flowers are green and gold,
  Chrysogonum virginianum.

A close second in my experience is Virginia creeper, Parthenocissus quinquefolia. This rambling and climbing vine has the same habit as poison ivy, but it usually have five leaflets rather than three.  The confusion comes because the younger shoots often sport leaves with three or sometimes four leaflets.  When I spot these I carefully trace the vine back a little ways to see if it also has leaves of five.  Some people have sensitivity to Virginia creeper, but the reaction is not as severe as the rash most people get from poison ivy. 

Virginia creeper is a vine with a similar habit as poison ivy. 
Most, but not all, leaves have 5 leaflets.

Another understory tree that has three leaflets is common hoptree or wafer ash, Ptelea trifoliata. This is not likely to be confused with poison ivy, although seedlings or growth from the base of the tree could cause some concern.  On the hoptree each leaflet does not have a distinct stem (petiolule), rather the leaf tapers sharply to the point of attachment.  While the leaflets of poison ivy are distinct with the central one considerably longer than the two lateral ones.  
Common hoptree grows well in shady locations not unlike poison ivy. 
Note how the leaflets lack distinct stems.

Aromatic sumac, Rhus aromatica, is less commonly encountered.  In the wild it is an upright shrub.  But in the landscape trade there is a shorter, spreading cultivar called ‘Grow Low’ that is becoming very popular.  When I’ve bumped into mine in the woodland edges I froze for a second until I noticed that the leaflets have different lobes and the leaflet stems (petiolules) are all the same length.  On poison ivy the middle leaflet has a longer stem than the other two.

The leaflets of aromatic sumac tend to have rounded lobes concentrated at the tips.

White avens, Geum canadense, has a number of leaf forms.  Some of its basal leaves can have three leaflets but they are not particularly glossy and are generally rough in texture.  Also this species grows in clumps, it is not viney.  


The younger leaves of white avens tend to have three leaflets.  To the lower left you
can see some of the more complex leaf forms.

Barren strawberry, Geum or Waldsteinia fragarioides and the non-native W. ternata, have leaves of three, but the leaf margins are more deeply toothed and the leaflet stems are all very short.
The glossy leaflets of barren strawberry appear to merge together looking
 more like lobes than separate leaflets.

  Mock strawberry, Potentilla  (or Duchesnia) indica, is another prolific ground cover with three leaflets.  It’s leaf margins are regularly toothed and it’s habit is different, spreading by stolons, not vining.  
The leaf surface of mock strawberry is much rougher in appearance than poison ivy.

Golden Alexanders, Zizia aurea, has leaflets that are twice divided, 3 sets of trifoliate leaflets (biternate).  The leaflets are ovate to lanceolate with finely toothed edges.  The long petioles may give the impression of young poison ivy stems.  
Leaflets of golden Alexanders can be seen in the circle at bottom right. 
Also present in this image is Virginia creeper and mock strawberry.

The native clematis, Virgin’s bower, Clematis virginiana, is a weak-stemmed vine with three part leaflets.  While you would want to routinely test the vine strength to distinguish it from poison ivy, an examination of the veins on the leaves would show the difference.  Virgin’s bower has a palmate pattern, with the major veins radiating from a single point; whereas poison ivy’s veins branch out along a central middle vein.  
The ribbed stems of virgin's bower are too weak to support itself
 and it needs something to climb on.

The list of trifoliate plants seems to go on and on.  After I thought I had this pretty well wrapped up I took another look and noticed the leaves of Jack-in-the-pulpit, Arisaema atrorubens, and that reminded me of the trilliums.  These can be recognized by their relatively large leaf size and regular arrangement of leaves.  Arisaema leaves are in a ‘T’ arrangement and those of trilliums are arranged in a regular triangle pattern (120 deg apart).  Can you think of any more poison ivy look-alikes to be on the watch for?

Friday, May 22, 2020

Vinca Replacement




Ever since we moved here 7 years ago I’ve wanted to replace the Vinca (V. minor) from our shady driveway turn-around.  Because I was new to the Mid-Atlantic area I didn’t want to do a wholesale replacement with something I wasn’t sure would work in this mostly shady, dry environment.  So I took a piecemeal approach, trying a little of this and a little of that, leaving most of the vinca in place.  This year I’ve decided to get more aggressive with the replacement, adding some successful species and trying some more new ones.

This was the next area for vinca removal.  It gets morning sun and open shade later in the day. 
It is framed on the right and left with test plantings of Heuchera and foam flower.
My primary reason for getting rid of the vinca is that it is an invasive species.  It is able to creep out of managed landscapes and run rampant in forested areas forming a dense ground cover that excludes native species.  From an aesthetic standpoint, while verdant, it can be rather boring and lack personality. Because of its ability to form thick foliage mats it tends to block out other less competitive species and creating a monoculture, at least on the ground plane.  

Most of the plants I have tried have survived the dry shade, but only a few have competed strongly against the viney invasive.  In all, I have tried nearly 25 native species in this area.  Strong competitors include Jack-in-the-pulpit (Arisaema triphyllum), green and gold (Chrysogonum virginianum), hayscented fern (Dennestadtia puntiloba), bigleaf aster (Eurybia macrophylla), Heucheras (I’ve had success with H. villosa and the cultivars ‘Citonelle’ and ‘Palace Purple’), twinleaf (Jeffersonia diphylla), Virginia creeper (Parthenocissus quinquifolia), zig-zag goldenrod (Solidago flexicaulis), merrybells (Uvularia sessilifolia), golden Alexanders (Zizia aurea), and the low-growing shrub sweetfern (Comptonia peregrina).  Also the non-native variegated Solomon’s seal (Polygonatum odoratum variagatum) is doing well (I imagine the larger native P. commutatum would also do well).  These are able to grow and spread without much help from me.  

Species that survive the conditions but need some help to keep from being overrun include wild bleeding hearts (Dicentra eximia), Alleghany spurge (Pachysandra procumbens), hoary mountain mint (Pycnanthemum incanum), smooth aster (Symphiotricum laevae), foam flower (Tiarella cordifolia), sedges (white-tinged sedge Carex albicans and pensylvanica, and there are some more robust wild ones like loose flowered sedge, C. laxiflora, that do very well).  Barren strawberry (Geum fragarioides, formerly in the genus Waldsteinia) should work well under these conditions, but in my case it seems to struggle.

Species that would be overrun without intervention include Meehan’s mint (Mehania cordata), woodland phlox (Phlox divaricata), and Labrador violet (Viola labradorica).  The only total failure was partridgeberry (Mitchella repens).  This tough little plant does not like to be covered, so between the vinca and the pine needles piling up it didn’t stand much of a chance. 

In this year’s planting I’m adding another sedge, ivory sedge (Carex eburnea), also wild geranium (Geranium maculatum) and, though I’m doubtful about this one, wild columbine (Aquilegia canadense).  I also have some downy wood mint, Bleiphila ciliata, which I started from seed that should do well in dry shade.

On the west end of this planting which gets a little afternoon sun, you can see the
ground hugging green and gold (now in bloom) and the much taller golden Alexanders (to the right).
Other plants include wild black raspberry, which appeared on its own, and several
volunteer trees that need to be pulled out.  
One of the features of vinca that is hard to copy with many native species is that it looks good (that is, pretty much the same) throughout the year with relatively little maintenance.  This is a great attribute from a design standpoint, but that does not make up for its invasive tendencies and relatively low ecological value.  Of the native species mentioned here green and gold and the sedges are evergreen (or nearly so) and the heucheras and foam flowers look good for most of the year.  Where there is sufficient moisture golden ragwort (Packera aurea) would be a very good evergreen choice.  


In the foreground you can see how Pennsylvania sedge pokes through gaps
 in the Virginia creeper (5-leaflets).  The sedge remains green throughout the year,
but looks a little ratty come January.  Another strong presence here is the zig-zag goldenrod,
with its ovate leaves, in the left and center of this image. 



Clearing this area took about 45 minutes.  Much of the time was consumed 
separating the vinca from the good soil after it had been pulled.  The pulled vinca 
was segregated to dry out and die before being put onto the debris pile.

Clearing the new planting space was surprisingly easy.  Since the area was thick layers of decomposed pine needles, the soil was very loose and most of the vinca could be removed with a 4-tine garden cultivator.  What didn’t come out with the cultivator was hand pulled.  I’m sure some bits of vinca remain and these will be addressed as they pop back up through the mulch.  I like using the fork because it hooked on the vines and it minimized damage to the deeper tree roots. 

Most of the new plants are in.  The most obvious are the heuchera and foam flowers. 
In addition to the wild geranium, columbine and ivory sedge are more
zig-zag goldenrod at the back of the planting and Labrador violets to the front edge. 
You can see the garden cultivator I used lying to the left.
Another means of vinca removal is cutting it back low then covering with a layer of cardboard, then mulch or clean soil.  This method would be better where the vinca is more firmly rooted.  I’ve tried spraying it with glyphosate, but the kill rate seemed rater low.

Here's the completed planting from another angle.  The new plants are mostly on the right edge
(see the little white tags?)  In the center of this view are established heuchera and foam flowers.
Using a variety of plant species in this area allowed me to tailor the planting to fit the variations in the site conditions: deeper vs. partial shade, arid vs. average moisture, etc.  Using plants with a tendency to spread both above ground, like foam flower and green and gold, or below the surface, like hay-scented fern helps cover the ground more quickly and allows the plants to migrate through the site to find their best conditions.  The variety also increases the biodiversity, extends the periods of bloom and provides more variation in form and color. 

I think for the next phase of vinca removal I will move to the middle of bed and try some taller species like the great Solomon's seal, white wood aster and more hay-scented fern.