Plans for 2022

For 2022 I have a smaller list of plants that I will be adding to my landscape than in years past.  There are a number of reasons: I’m running out of space to tuck in new plants, I’m moving more seedlings of successful native species around, rather than purchasing new plants, and I am getting more selective about using regionally native species.  However, I am not beyond adding a few species for decoration.  New plants that I am adding are prairie willow (Salix humilis), creeping lespedeza (Lespedeza repens), a wild type smooth hydrangea (Hydrangea arborescens) and I’m trying winecups (Callirhoe involucrata) again in a less competitive environment.

I have been looking for native willows to replace the mounds of forsythia on my property.  Willows bloom early in the spring, like forsythia.  But unlike them, willows do provide a benefit to the native insects: early flowers for bees and as a host species for a number of insects.  Early on I put in some native pussy willows (Salix discolor).  These are doing well but mine tend to have a taller upright form (nearing 20’) rather than a more rounded shape that I was looking for.  Prairie willow has the form I’ve been after, 4-7’ tall with a loose vase-shaped habit.  It is also tolerant of drier conditions than most willows.  I’ve got some on order, so we will see later this spring if my search is finally over. 

Pussy willow blooms at about the same time as
forsythia (shown here in the background).  

Another species that I have been trying to expand in my landscape is smooth hydrangea.  Most of mine are the huge mophead type, most likely ‘Annabelle’.  These grow really well with lots of flowers, but since most of these flowers are sterile, they offer little benefit to wildlife.  Two years ago I planted planted some tiny pots of the ‘Haas Halo’ cultivar.  These were highly rated in a recent study done at the Mt. Cuba Center.  These have large lace cap flowers which consist of mostly small fertile flowers in the center surrounded by a ring of large sterile flowers.  The plants grew to over 2’ tall last season, so I’m hoping I might see some flowers this year.  To build on this diversity I ordered a wild-type smooth hydrangea to add to the mix.  Wild-type plants usually have smaller flowers than the cultivars, but I’m hoping to see a benefit in the production of some seeds that could help the birds.

These wild hydrangeas are growing along the Potomac River
in Maryland. This photo was taken in late April. 
It seems kind of early for buds to be forming, considering
that 'Annabelle' hydrangeas normally bloom in June.

An ongoing project that I have is to find replacements for vinca, particularly in dry shade.  I am expanding the scope to include a replacement for the yellow archangel (Lamiastrum galeobdolon) that is spreading in my pine woods.  Last year I got some round leafed tick trefoil (Desmodium rotundifolium) for which I had been searching for 10 years (we’ll see how that has overwintered). It trails along the ground sporting three round leaflets on each stem. While examining catalogues I came across another trailing plant for dry shade, creeping lespedeza (Lespedeza repens).  While not super attractive on its own, it may work nicely in a matrix planting. 

I didn't have a photo of the Lespedeza, so I'm sharing an image
from my botanical sketchbook.  Included are some notes on
how to tell Desmodium and Lespedeza species, both
members of the pea family, apart.

The wine cups are an exception to my focus on regional natives.  These are native more to the mid-west and southern plains, than to the east, but I became enamored with them ever since I saw them in a field in the Ft. Worth area.  I was able to grow them in the Boston area and had them for awhile here in Maryland.  The problem was that they were not able to compete with dense growth of asters, goldenrods, and Virginia creeper that surrounded them.  This time I will plant them where they have a little more of their own space to get established.

The magenta flowers of wine cups are hard to miss.  It has a
sprawling habit and can form a ground cover 
where competing vegetation is sparse.

As I mentioned above (and last year at this time) I will also be moving many native seedlings out of my vegetable garden, particularly Rudbeckia sp., Monarda fistulosa, Asclepias tuberosa, and Echinacea purpurea, and into the beds where I am fighting Japanese stiltgrass.  I started that process last year.  It’s too soon to see a difference, though some of the transplants appear to have overwintered.  Their real value will be if they are able to reseed themselves and become self-sustaining.

Squirrel baffle

Our squirrels have figured out how to get into the bird feeder that was hanging from a branch of a tree. This was despite a series of impediments that I put in their way. It was a somewhat tolerable situation for awhile; however, when they figured out how to knock the entire feeder off of its hanger and onto the ground, it was time for a change. So we moved it to a shepherd’s hook. I thought the narrow metal pole would be hard for them to climb. NOT SO! After a day they were climbing the 1/2” pole and clearing out the bird seed. Searching for another solution, I saw baffles advertised online and that seemed to be a good solution, but I didn't want to shell out upwards to $50 on something that I was not certain would work. So to test whether this would out with our squirrels I looked into making one from materials I had on hand.

Most baffles that I saw for sale were essentially sheet metal cones at least 18" in diameter that are attached to the central pole. The conic shape keeps debris from getting trapped on top and makes it a little harder for the squirrels to get a hold of. I was able to make this one from 10” aluminum flashing left over from a roof repair.

1) Here are the two semicircles with the notch
cut in the center. Note the triangular tab
on the left hand piece made by bending
down the edge.

To form the baffles I cut semicircles 20" long x 10" wide from my stock of aluminum flashing using tin snips. I cut a a notch about 1//2" wide x 3/4" deep on the edge of each piece of the stock 10" from the end. This will fit closely to the pole. To increase rigidity of the final cone I bent a triangular tab from the center cutout to the edge, about 3/4", on each piece. (Image 1)

To join the pieces together I overlapped one seam by about a half inch and drilled holes for two small #6 machine screws and bolted them together. To get the fit just right I put a 1/2" rod into the center hole and pulled the two free edges together to form the cone. Now I could drill the final two holes along the edges of the stock to ensure a good fit. (Image 2)

2) The two pieces were joined along one edge with
 machine screws and nuts.  To ensure a proper fit,
 the holes for the second pair of screws were
 predrilled after fitting the baffle onto a 1/2" post.

3) Here's a closeup showing the two taps formed by
 folding down the edges.

Mounting the cone on the shepherds hook was easily accomplished by attaching a slightly oversized hose clamp at the desired height on the pole. The cone was mounted by removing two of the machine screws, opening the cone, then fitting it on the pole above the clamp. The screws were reattached, in place, to secure the cone. Having the cone 'float' on top of the clamp makes it more difficult for the squirrels to get hold of. (Images 3 & 4)

4) I had this hose clamp on hand that was large
enough to keep the baffle from sliding down.

Success!  Here's the final product with
birds happily at the feeder and a pair of squirrels
on the ground waiting for seeds to fall.

With the homemade baffle in place the squirrels were no longer able to get directly into the feeder.  Instead they just hung around the edge waiting to see what hit the ground.  Serendipitously I was given a nicer looking store-bought baffle at the end of last year.  I will be using that one in 2022.

This store-bought baffle has all the features of my
homemade one, except maybe the rugged good looks.

Why Won't My Garden Grow?

 I’ve noticed that I’ve been having less success growing vegetables from seed in my garden over the past few years.  That is particularly the case for small seeded crops like lettuce and chard.  This is in spite of increased organic fertilization.  True, I don’t water as much as I should for seedlings, but I never do.  I tend to rely on rain.  Still I have become suspicious that something else may be going on.  This has led me to consider allelopathy.  My question is whether there is something that is growing or has grown recently in the garden is affecting the ability of new seeds to germinate and develop?

Garden in mid-June: Vegetables still small in
 relatively clean beds, but Monardas
and Rudbeckias are coming on strong.

Allelopathy refers to the beneficial or harmful effects one plant has on another. It arises from the release of allelochemicals from plant tissues though leaching from leaves or roots, volatilization or decomposition of plant parts in or on the soil.  Through these allelochemicals one plant is able to suppress germination or development of other plant species in the immediate area.  In some cases these chemicals may have a beneficial effect on some neighboring species while having a negative effect on others.  There is a lot of research in this area, particularly to find crop plants that are able to produce their own weed suppressive chemicals rather than relying on added herbicides.

There are a couple of non-traditional practices that I have been employing in my vegetable garden that I am beginning to question.  One is that I allow native species to run rampant along the edges and between the rows of vegetables, particularly wild bergamot (Monarda fistulosa) and black- and brown-eyed Susans (Rudbeckia hirta and triloba).  The other is that I leave the roots of the previous year’s plants in place.  I just cut the old plants off at ground level and throw them into the compost pile.  I do this as a means of increasing the organic matter in the soil and reducing soil disturbance. 

Following the adage, “a month in the laboratory can often save an hour in the library” (Frank Westheimer) I decided to do a little research first.  I searched the internet for information on the allelopathic potential of all the native and non-native species that are growing in my vegetable garden.  After searching those, that I turned to looking at the vegetable themselves. 

The tables below list many of the weeds, native species and lastly the vegetables that are common in my garden along with the existence of any documented evidence that these plants possess any allelopathic properties.

Garden Weeds:

Common Name	Botanical name	Evidence of Allelopathy
Chickweed	Stellaria media	Yes
Ground ivy	Glechoma hederacea	Yes
Hairy bittercress	Cardamine hirsuta	No
Indian strawberry	Duchesnea indica	No
Mulberryweed	Fatoua villosa	No
Ladies thumb	Polygonum persicaria	Yes
Nut sedge	Cyperus esculentus	Yes
Persian speedwell	Veronica persica	Yes

 

Native Annuals & Perennials:

Common Name	Botanical Name	Allelopathic?
Annual sunflower	Helianthus annuus	Yes
Common Milkweed	Asclepias syriaca	Yes
Butterfly weed	Asclepias tuberosa	No?
Common and Daisy Fleabanes	Erigeron philadelphicus and annuus	Yes
Honeyvine	Cynanchum laeve	No
Wild Bergamot	Monarda fistulosa	No
Scarlet beebalm	Monarda didyma	Yes
Purple Coneflower	Echinacea purpurea	Yes
False sunflower	Heliopsis helianthoides	No
Goldenrods	Solidago sp.	Yes (some species, at least)
Browneyed Susan	Rudbeckia triloba	No
Wild Blackberry	Rubus sp.	?
Sealheal	Prunella vulgarus	No
Pennsylvania smartweed	P. pensylvanicum	Yes
Wingstem	Verbesina alternifolia	No*

*Golden crownbeard, V. encelioides, a native of western North America does have allelopathic properties.

Garden Vegetables:

Vegetable	Botanical Name	Allelopathic?
Arugula	Eruca vesicaria ssp. Sativa	No
Basil	Onicum basilicum	Yes
Collards	Brassica oleracea var. viridis	Yes
Cucumber	Cucumis sativus	Yes
Green Beans	Phaseoleus vulgaris	Yes
Lettuce	Lattuca sativa	No
Peppers	Capsicum annuum	Yes
Squash	Cucurbita pepo	Yes
Swiss chard	Beta vulgaris var. cicla	Yes
Tomato	Solanum lycopersicum	Yes

 

While doing these searches I came across some interesting studies on the potent allelopathic effects of many invasive species.  This is one of the factors that allow invasive species to outcompete native ones.  One study treated radish seeds with the aqueous extracts from leaves of a number of invasive species.  The radish seeds were then evaluated for germination rate and root growth.  The following list is ranked in order of negative effect on germination, most to least:  Ailanthus altissima, > Microstegium vimineum, Alliaria petiolata, Celastrus orbiculatus,> Ligustrum vulgare, Rosa multiflora, Rubus phoenicolasius, and Acer platanoides.  There are multiple studies that document the allelopathic effects of Japanese knotweed, Polygonum cuspidatum.  It seems that many species of the genus Polygonum have some allelopathic character.

From this research it looks like the fleabanes (Erigeron annuus and philadelphicus) and purple coneflower would be the most likely allelopathic culprits among the native species in my garden.  However, most of the allelopathic candidates on these lists are from the weeds and garden vegetables.  Of these, ground ivy, nut sedge and ladies thumb are the most prolific weeds in my garden.  Among the vegetables in my garden, collards, peppers and cucumber are the most likely suspects to be causing some troublesome effects.

Allelopathy experiments.  In general experiments that measure allelopathy are tricky to interpret.  Many are based on bioassays, where the allelopathic effect is measured by such things as the germination rates and root growth of a target species.  In many cases radish or lettuce seeds are used.  Many of these studies use extracts of leaves, stems or roots of the species being studied applied at various concentrations to isolated seeds of the target species in a Petri dish.  Another approach is to test the soil itself.  Due to the complex nature of plant-soil and plant-plant interactions, most studies on allelopathy are correlative rather than causative. 

To help me understand whether there was a problem with the soil (and all the things that come with it), or the cultural effects like moisture and sunlight, I decided I would try a bioassay comparing surface soil samples from various parts of the yard and garden.  I tested to see how each of these soils affected germination and growth of some lettuce seeds which had performed well when started indoors this past spring.

Germinated seeds:  Control (top);
near wild bergamot (middle);
 under English walnut (bottom)

I adapted a procedure from Environmental Inquiry/Cornell University for performing lettuce seed bioassays using materials I had on hand.  I took three samples of surface soil, 0-1/2” deep, from each area of interest.  This is the zone that I normally plant small seeds like lettuce in.  I mixed the soil samples in a baggie then pulled out about a tablespoon’s worth.  This was put into a fresh baggie (as I didn’t have any Petri dishes) and moistened with a few drops of water to make the soil damp, but not wet.  I disinfected the lettuce seeds in dilute bleach, according to the procedure, and then put 8 seeds into each baggie.  The baggies were sealed, put into the dark for 5 days at 60-80°F.  I used a moistened, peat-based seed starting mix as the control.  Samples were taken in November so there was no active growth of vegetables except for the sample near actively growing collards.  I tested the following areas: 1) garden soil under green beans, near daisy fleabane; 2) garden soil under wild bergamot; 3) garden soil near where tomatoes and cucumber had grown; 4) garden soil near collards; 5) typical lawn soil (fescue and weeds); 6) under an English walnut with vinca groundcover.

After five days I separated out the germinated lettuce seeds, counted the number of germinated lettuce seeds and measured the length of the roots.  I found I was able to pluck out the germinated seeds from the soil in the baggies by suspending the entire sample in water with a little dish soap.  This allowed the soil to fall away from the roots without damaging them.  The root growth measurements had a lot of variation.  This is not too surprising considering the many uncontrolled variables, like variable soil moisture and soil contact within each baggie, and small sample size.

Graphical comparison of various soil samples on germination and root
growth of 'New Red Fire' lettuce seeds.

Results and Conclusions

While the differences in root length and germination rate among these samples are not highly significant, due to the small samples size, there is an indication that the soil around the collards is not as favorable to seed germination and growth as any of the other garden samples and is on the order of that for soil under an English walnut tree.  (English walnut, Juglans regia, is much less allelopathic than our native black walnut.)  These results also indicate that the presence of wild bergamot (Monarda) is not detrimental to the initial stages of seed growth.  Another indication was that root growth in the soil around the green beans was less than the control sample.  This is consistent with a study that looked at the effect of leaf extracts of several lines of common beans on seedling growth, including lettuce.  That study made no mention of the effect on seed germination.

Lettuce or radish seed bioassays are also good for checking for herbicide residues in soils and mulches.  General information about testing whole soil samples for herbicide residues can be found at this link from NC State.

Based on the literature it seems like many of the plants in my garden have some degree of allelopathic behavior.  This brings up another important question; how long does that effect last.  The sense I get is that it’s more on the order of weeks than months.  In field trials some brassica family cover crops have shown allelophatic effects on the order of weeks to months after being tilled in. I found another post discussing the use of cover crops, many of which are allelopathic.  It suggested waiting 3 weeks after tilling them in before planting.  Leaving allelopathic plant residues in place as a mulch, will increase the time over which they have the suppressive effect.

 So, based on my little experiment and all the literature I scanned, it seems there is no single clear cut culprit exerting a negative influence on my gardens fertility.  This research has led me instead to a list of suspects and actions to control their effects.   It may be that my practice of leaving roots in the ground, particularly the collards, over the winter may be negatively affecting my gardens ability to grow grow directly from seed. I will need to dig these out at least a month before planting in the spring.  I will also pull out any remaining roots of the curcurbits and chard which remain, as well.  The ubiquitous weeds, particularly chickweed, ground ivy, and ladies thumb need to be removed, especially during the growing season.  As much as I like the prolific flowers of the native daisy fleabane, I will be removing those from the vegetable beds, as well.

Another less traditional garden practice I have been using is flame weeding.  This involves using a hand-held propane torch to kill weed seedlings before they can establish.  This was done prior to planting, or transplanting crops.  An advantage of this practice is that it doesn’t disturb the soil surface.  I have not looked into any literature on possible negative effects of this practice, but for next year I will not use this method in the growing beds themselves. 

So with these changes we will see if I get any better results in the garden, or will I need to dig deeper?

Wishing you all the best for the New Year!!!