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.

Fighting Garlic Mustard with Fire? Or Something Else...

A couple of years ago I added a garden torch to my arsenal of tools to maintain the landscape.  Fire can be a natural and effective tool in controlling invasive species and is one of the better ways to maintain a prairie ecosystem.  But, fire can also get out of control and its effectiveness is diminished if it is not timed properly or its intensity is not sufficient to destroy the target species.  On the garden scale a garden torch is a good way to kill weeds growing in cracks in a drive or walkway.  It is also effective at killing young seedlings, particularly annuals.  I found it particularly useful for  for clearling plants away from the partially buried wire fence around the vegetable garden.  Perennials and established plants require much more heat to kill them.  For established weeds repeated burning 2-3 weeks apart may be necessary.  Though it seems counter-intuitive, flaming moistened soil is more effective at killing young plants and seeds than dry soil because the moisture helps conduct  the heat through the soil.

Here's my Benzomatic garden torch.  It is light weight and a good size to fit into tight spaces. 
The one pound tank lasts an hour or so, depending on how big a flame you use.  

I originally got my torch to use on Japanese stiltgrass.  While spring burning does kill the sprouts effectively, other plants are actively growing at this time and the fire will set those back as well.  Also stiltgrass germination occurs over an extended time period, so multiple burns would be necessary.  For stiltgrass in a cool season lawn, burning in late summer, while the perennial grasses are in summer dormancy, is very effective at preventing the stiltgrass from setting seed.

This success with stiltgrass got me to thinking about using the torch on garlic mustard, Alliaria petiolata.  Garlic mustard is a monocarpic biennial. It spends its first year as a rosette of deeply reticulated, reniform (kidney-shaped) leaves that builds up energy reserves in its fleshy white roots.  The following year it sends up a 2-4 foot flowering stalk in mid- to late-spring. It seems that winter time might be a good time to take out the garlic mustard.

Winter rosette of garlic mustard.

In the past when I have tried to burn garlic mustard I found I had to hold the flame on the plant for a long time before I could see much damage.  Before burning through a lot of propane, I decided to do a little research on using fire against garlic mustard.  The U.S. Forest Service has reports that document the effects of fire on a number of important plant species, including invasives.  Follow this link to the Forest Service report on garlic mustard.  A study authored by Victora Nuzzo for the Illinois Department of Conservation in 1990 compared the effectiveness of fire, herbicide and cutting for the control of garlic mustard.  They found that for fire to be effective it needed to be moderately intense and carried out in early spring.  Ideal burning conditions were often not available.  Herbicidal spray treatments were most effective in early fall and spring, timed for when native vegetation was dormant and thus less susceptible to the herbicidal effects.  One study out of Ohio showed that winter-time application of glyphosate when temperatures were between 25-45 F was very effective at killing garlic mustard rosettes.

Cutting plants after seed formation had begun in mid- to late-summer was very effective at reducing the number of plants in subsequent years.  Cutting at ground level resulted in nearly complete mortality, while cutting a couple of inches above the soil surface was only about 70% effective at killing the plant.  Since flowers and seeds continue to develop on cut stems, it is important to bag and dispose of all the garlic mustard cuttings.

Pulling mature garlic mustard is also very effective, and can be done anytime.  As with cuttings, if there are any flowers present the pulled plants should be bagged and disposed of.  While completely non-toxic, pulling garlic mustard is labor intensive (pulling and clean-up) and disturbs the soil.  This allows for the germination of additional seeds buried in the soil.

Here are some of the interesting garlic mustard facts that I came across while researching this post:

•        Seeds lie dormant for a year before germinating.  This means you may not see the effect of control measures on new seedlings until the second growing season.
•         Flowers are self pollinating; many are already pollinated before the flower opens.
•         Flowers can photosynthesize.  They can continue to mature to form seed even after they have been cut or pulled.
•        Plants are monocarpic.  They will continue to live until they set seed, even multiple years.
•        Seedling mortality is high, 80-90%, during their first year.  More effort should be expended on removing maturing plants particularly in late fall to early spring.
•       Of the common herbicides, glyphosate and triclopyr are very effective at controlling garlic mustard, 2,4-D is not.

So, Burn or Not?

So to answer the original question, should I use fire to control my garlic mustard?  The answer, for me, is no.  I will need to use a combination of tactics appropriate to the situation and season.  Winter spraying with glyphosate will be easier and more effective than fire at my location.  In the spring, pulling or carefully targeted spraying would be most effective.  And for those plants remaining in the late summer, cutting close to the ground or continued pulling will be in order.

To test this I will target spray with 3% glyphosate in a section of the woods in February if (when) we get a stretch of days in the 40’s with no rain and see how that compares to untreated areas.  (February seems a little early, but we are in the 60’s in early January, so plants may be getting woken up a few months before normal.)  Rather than blanket spraying I will try to target the spray onto existing rosettes.  One of the reasons to use target application is to avoid those few natives that are still in leaf through the winter. 

Some native plants that may look similar to garlic mustard rosettes include violets, Heuchera, Tiarella, and white avens (Geum canadense).  Ground ivy (Glechoma hederacea) and common mallow (Malva neglecta) are some weeds that look similar, but are not currently on my hit list.  (I found no studies that indicated that ground ivy is susceptible to herbicides in winter.  Based on that I wouldn't waste time and materials treating it in the winter.)

Compare the palmate lobed leaves with the deeply veined (reticulated), bright green leaves
of the garlic mustard.  Here, pulling is the only option for removing the garlic mustard.

The leaves of foamflower are distinctly lobed.  The vein pattern
is different from that of garlic mustard.

Golden ragwort has regularly toothed leaf margins and a more linear vein pattern.

White avens over winters as a loose rosette of leaves.  Though most winter leaves
 have 3 lobes, some appear roundish and vaguely similar to garlic mustard.

The leaf shape of common mallow is similar to that of garlic mustard,
but the vein pattern is different.

In areas where I am more actively managing the garlic mustard I will continue pulling plants through late spring (before flowering).  In late summer I will see if there is a practical way to cut the plants close to the ground without leveling the surrounding vegetation.  Otherwise, keep pulling!

This table summarizes the garlic mustard control methods mentioned in this post.

Summary of Garlic Mustard control measures

Method	Timing	Pros	Cons	Effectiveness
Fire	Late Fall to Early Spring	Non-toxic	Difficult to achieve ideal conditions; Need to keep under control	A good moderately hot fire is effective, but difficult to achieve.
Herbicide Spray	Dormant season	High kill rate; can be targeted; no soil disturbance	Spraying toxic materials; may affect non-target species	Dormant season spraying reduces damage to non-target species.
Cutting	Summer, after flowering	Non-toxic; cutting at ground level nearly 100% effective; minimal soil disturbance	Labor intensive; must dispose of stems/flower stalks; use of weed whacker causes collateral damage.	Very effective when done right.
Pulling	Anytime ground is soft and easily worked	Non-toxic; very effective as long as most of the root is removed	Labor intensive; disposal of pulled plants required once flowers are present; soil disturbance	Very effective

Planting Plans for spring 2015

Every year brings another opportunity to grow my native plant collection.  This year I'm focusing on 4 areas:  Clean up and replanting around the swimming pool, clean up and expansion of the meadow, replacing the vinca along the driveway and build up a privacy hedge with the neighbor.  After learning a bit about the current conditions, what is already here and what might be expected to grow here naturally, I've put together a shopping list of natives to get this year.

This moss phlox is pretty happy growing along the pool deck,
A good portion of it is on the concrete slab.
The colors can be intense, so I use mostly one color at a time.

The area around the swimming pool is infested with common evening primrose (Oenothera biennis).  While native, there is just too much of it and it is not that attractive close up.  The soil is mostly a fast draining fill with a moderately high pH (ca. 7.5).  Since this is far from native soil I put a greater focus on what would look good growing in this setting.  Since I had already started using this area for plants native to Texas (my wife's home state) I will be adding two of my favorites, Wine Cups (Callirhoe involucrata) and Indian Blanket (Gaillardia pulchella).   I got some seed on a recent visit to the Wildflower Center.  These will be great for the full sun areas and they tolerate alkaline soils.  The moss phlox could use some bolstering up as well.  I am attempting to remove the English ivy from the enclosure and this phlox seems to be a good candidate to fill back in.

This species of wine cups grows close to the ground, filling gaps around taller plants.
Seed requires a hot water treatment and  30  days cold stratification for germination. 

This is the annual species of Indian blanket, Gaillardia pulchella.

Small's Penstemon is long blooming in shady locations.
The contrasting lavender and white blossoms show up at a distance.

In the shadier areas I will be trying out Greek Valerain (Polemonium reptans aka Jacob's Ladder) and Small's Penstemon (Penstemon smallii).  Despite its common name the valerain is actually a native to the of the US.  This had confused me for a while.  Looks like the name Greek valerain is used for a number of species in the Polemonium genus.  One of them with particularly showy flowers, P. caeruleum, is a European native.  P. reptans grows more like a ground cover

I've ordered some more Indian Pink (Spigelia marilandica) for an area in the pool enclosure with more moisture and organic soils.

This cottonwood seedling appeared in the vegetable garden.
I'll transplant it this spring to a moist part of the new meadow.

I have an area that has been overrun with invasives that I am trying to convert to a meadow.  I cleared half of it last year and hope to finish this spring.  After removing the bad guys I am backfilling with native species.  I realize that I'm making more work for myself by trying to kill off invasivies at the same time as introducing new plantings.  By planting mostly shrubs I think I can more easily manage the area with an annual mowing/whacking of the undesirable plants.  For the right way to convert a weedy area to a meadow or prairie check out this link.

Last year I planted an American plum (Prunus americana) and several elderberries (Sambucus canadensis).  This year I will add some chokecherries (Prunus virginiana) and smooth sumac (Rhus glabra).  I also have a Cottonwood (Populus deltoides) seedling to put on the edge.

The pawpaw blooms in early May,
just before the leaves open up.  

Way in the back I have a large grove of Pawpaw (Asimina triloba) trees.  I've been watching them for 2 years and I have yet to see any fruit.  Since pawpaws produce better with cross-pollination, I will be adding a couple of new individuals to the area,  It is possible that my entire grove is really just one clone.  We'll see if this helps, in a couple of years.

These goldenstar have more than doubled in size after a year in the ground.
I'll get some more to speed up coverage.

In the shady area around the driveway I have been ripping out the vinca and replacing it with shade tolerant natives.  I started with foamflower (Tiarella cordifolia) and Heucheras and these are taking hold.  In addition to these I've seen some really good results with Goldenstar (Chrysogonum virginianum, aka Green and Gold) in open shade areas.  These are relatively easy to find in a regular nursery, sometimes marketed with the plants that you can walk on.  Another plant that I've used in dry shade is big-leaf aster (Eurybia macrophylla), It has dense foliage and spreads by rhizomes so it should do a good job competing with the vinca.

This shiny summer foliage pf aromatic sumac turns red and orange in the fall.
We'll see how it performs in a shadier location.

The boundary between our nearest neighbor is defined with a double row of white pines.  At 40+ years old they are now limbed up fairly high and not providing much screening.  We have already put in a juneberry (Amelanchier canadensis), hazelnut (Corylus americana) and Hoptree (Ptelea trilfoliata).  There was also a pawpaw already there, doing a pretty good job despite the drier conditions.  We are looking to add some additional shrubs to fill in this gap and obscure the view.  A local native plant nursery has listed maple-leaf viburnum (Viburnum acerifolium) for sale this year.  I've been told that this is a very difficult shrub to propagate.  It does well in shady woods so I'm looking forward to trying it here.  I should get two since they don't self pollinate.  I am also looking to get some aromatic sumac (Rhus aromatica).  The wild form grows 5-12 feet, just the right size for our area.  I already have some of the 'Gro-low' cultivar.  At about 3 feet it is a great ground cover shrub for many difficult locations.

Now with may list in hand, I can hardly wait until spring!