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

Surprise Plants

Living in a more rural area means that there is the possibility that there are still many native species lurking just out of sight.  Here are some of the plants that I have found growing spontaneously around our property.  Most of these have benefited from the removal of invasive species.  Reducing competition for light allows for germination from the seed bank and stronger growth overall.  Removing the cover, especially Japanese stiltgrass, also makes it easier to see what all is growing.  

The scalloped leaves along the stem made me think
that this was ground ivy, but the flower on top
quickly showed me to be wrong.

Among one of the first species of native annuals I tried to grow was clasping Venus looking glass, Triadonis perfoliata.  I had no luck in getting the seeds to germinate under controlled conditions (moist stratification, sterile soil, under lights, etc.)  This past spring, I came across some blooming plants as I was looking for some other seedlings in an area where I have been pulling out Japanese stiltgrass.  I can't say for sure that its emergence was due to reduction in stiltgrass, but it was much easier to find with less competition for space.  Since this species is an annual, continued success depends on it producing seed and getting that seed in contact with the soil.  Having the area less clogged with stiltgrass should help it along. 

When I first noticed it, I saw the clasping leaves on a long stem and thought it was ground ivy.  Before I could pull it I noticed the bright lavender flower at the end of the stem.  Closer examination shows that there were calyces in most of the upper leaf axils.  These had probably already bloomed out.  I will keep an eye on this area next spring to find this plant again. 

The round, glaucous stems on this bush indicated that this was some sort of raspberry. 
The berries were initially red, but all turned black over the course of a few days, so it some sort of black raspberry

When we moved here in 2012 many of the unmown areas that got any sun at all had the invasive wineberry, Rubus phoenicolasius, growing in them.  Fortunately this is not a strongly growing plant and it can be suppressed by cutting it back on a regular basis (at least once a year). It is also fairly easy to pull.  While the stems are covered with sharp bristles, these are not very stiff and will not penetrate my gardening gloves.  I was disappointed that I could not find any native raspberries (we have a ton of wild blackberries) growing in or around the woods.  In 2017 I started noticing a different berry plant showing up in various places, many of those that had been covered with wineberry.  The trifoliate leaflets and bluish blush on the rounded stems pointed toward some sort of raspberry.  (See this link to Illinois Wildflowers for way to tell raspberries and blackberry plants apart.)  It didn't matter which, as long as it wasn't wineberry (or more blackberry).  This spring these new plants flowered and produced fruit.  The berries were initially red, then turned black as they ripened.  While I have not nailed down the ID, it's a pretty good guess that these are native black raspberry, Rubus occidentalis.

I don't know if these are from an existing seed bank, or were brought in by wildlife.  Next year I will pay closer attention to the flowers to try and confirm the ID; although there are only three species of raspberries that are black, most are red.  If these came in via wildlife, they may be from some cultivated varieties rather than strictly wild.  On tasting the black berry I finally appreciate what the flavor 'black raspberry' really is like.  Jolly Ranchers have the taste right.   

Two years after I started removing the invasive species from this area,
these American germander have formed a hedge of their own.

American germander, Teucrium canadense, was one of the first native plants to emerge from what was before a dense hedge of wineberry, garlic mustard and Japanese stiltgrass.  Since this plant spreads by rhizomes and is a prolific reseeder it may be able to hold its own against the stiltgrass.  Peak bloom is in mid-summer at which time it is easily identified by the stamen arching out above the slipper-shaped, white to pale pink flower.

You can see the small white flower clusters coming
out of the stem at the bottom of this photo.

Sweet cicely, Osmorhiza claytonii, is a pretty common woodland edge native.  I usually find it along paths in partly to mostly shady wooded locations.  I usually notice it because of the deeply lobed bright green leaves and the hairs that cover the leaves and stems that catch the light.  As more invasives are removed from the understory small plants like this one are easier to spot.  Also as space opens up native like sweet cicely can fill in.

This large, about 5" long, trumpet-shaped flower is unlike most native species in our area. 
Is is actually a southwestern native but has naturalized as far north as New England.

Afterthe removal of a large pine tree I've been finding new plants cropping up all around it.  These were probably buried in the seed bank and were stirred up by the work crew or were just sitting there waiting for more light and moisture to encourage germination.  One plant that really surprised me was Sacred Datura or Angel's Trumpet, Datura wrightii.  Native to the western states, this plant is probably a garden escapee, possibly grown by the previous owner or flown in by birds. In colder climates this plant behaves as an annual though is is listed as cold hardy to USDA zone 4.

Though a little tattered Robin's Plantain seems to be
getting established in a shady portion of the lawn.

We have a number of fleabanes, Erigeron, growing here.  Most of the plants are either annual fleabane or Philadelphia fleabane, E. annuus or E. philadelphicus, respectively.  In a shady portion of the lawn (where grass doesn't grow well) I noticed a new white daisy-like flower.  It was growing up from something that looked like plantain.  While I'm not absolutely certain I'm pretty sure that this new find was Robin's Plantain, Erigeron pulchellus.  When it's in bloom I try to avoid mowing it so that it will have a chance to spread.  Since Robin's Plantain likes limy soils and has persistent green basal leaves it is a welcome addition to my natural lawn.

Stiltgrass Fall 2019

I'm continuing my multipronged attack on Japanese stiltgrass, Microstegium vineum, that I have been waging for about 5 years now.  Depending on where the stiltgrass is growing different techniques are more effective.

Here are links to some earlier posts on my campaign against stiltgrass: Spring 2019, Spring 2018, Fall 2017, Original Plan 2014, and Use of Pre-emergents.

Woodlands  In the  shady woodland settings pulling the stiltgrass through the summer and especially in late summer just before blooming has been pretty effective.  In several of these shady areas removing the stiltgrass before is sets seed has shown good results after two seasons.  It is important to continue to follow up year after year to prevent a re-infestation.  When I first started do this I used a weed whacker to cut very close to the ground and I left the cut grass in place.  In places where I removed the cut grass progress toward eliminating it seemed to go faster.  Also as other, hopefully native, species begin to fill in, weed whacking risks cutting out those species as well.  Now I've gotten to the point of hand pulling the stiltgrass and piling it up in segregated locations where any seed present will be less likely to spread.

Here are some clumps of Virginia wild rye growing under a young tupelo tree. 
This is a cool season grass, seen here in June.  By the end of summer
 it will be golden brown with arching seed heads.

Bottlebrush grass is also a cool season grass that like partly sunny sites. 
These early season grasses have a chance to shade the ground before
the stiltgrass begins maturing in July

In these locations I have been trying to have more native species fill in, by either encouraging the existing natives of adding new ones.  Virginia wild rye, Elymus virginicus, is a native grass that grows pretty well in the shade, as is bottle brush grass, E. hystrix.  Other species that are filling in on their own are Virginia jumpseed, Persicaria virginiana, and clearweed, Pilea pumila.   A variety of smartweeds are also increasing, but I fear many of those are non-native species.

Clearweed is a native annual that has had a banner year here in 2019. 
It grows well in shady locations.  

Meadows  I've been having more trouble in the open meadow sites.  Some of this is my reluctance to do anything but hand pull.  I am trying not to disturb the more desirable species that co-inhabit the meadows.  In one area that I have been hand pulling for 3-4 years I'm seeing a reduction, but it still has a long way to go.  This past spring I put some pre-emergent  in several meadow areas and saw a further reduction in stiltgrass density, but not an elimination.  I also tried burning a patch of ground in early spring but that had no noticeable effect on the amount of stiltgrass.  (That is consistent with what the Forest Service reports on the use of fire.) 

By virtue of how stiltgrass grows, sending out shallowly rooted runners to fill all available space, by the end of summer you will have a similar density of flowering stalks whether you have 10 or 50 seedlings per square foot.  (These are my impressions, not proven facts).  But having fewer rooted individuals means it gets easier to clear an area by pulling because so many of the stems are interconnected.  I will try the pre-emergent again this spring, but do the application earlier (read on below).  One of my concerns in the meadow is that the pre-emergent will inhibit some native species from growing/reproducing.  I did not go in and inventory what was or was not growing in the treated and untreated areas.  I did see smartweeds and tick trefoils, Desmodium panniculata,  growing in all areas.  Where stiltgrass was growing thickly the ground plane was essentially barren after the grass was removed.

In May stiltgrass seedlings are less than an inch tall.  The right side of the area
was treated with Dimension pre-emergent herbicide in the first week of April. 
The untreated side has a greater density of stiltgrass seedlings.  I expect that
 applying the herbicide earlier in the spring will further reduce the amount
 of sprouted stiltgrass.

This is the same area, photograph from behind.  The treated side (left)
 has a slightly lower density of stilt grass, but still
 most of the available space is filled with stiltgrass stems.

Removing stiltgrass from the lawn.  Pre-emergent herbicide is still showing very good results.  2 years ago I applied herbicide (Dimension^tm) around the 3rd week of March.  While in the spring of 2019 I waited until the first week of April.  Or using the forsythia bloom as an indicator of spring weather, mid-bloom in 2018 and late bloom in 2019.  Despite the presence of the herbicide I did see more stiltgrass seedlings in 2019, so I think applying the pre-emergent earlier may be more effective.  For folks in the Northeast and Mid-West  there is a website that helps with the timing of pre-emergent application based on degree days.   Another problem with getting stiltgrass out of the lawn is that repeated mowing can stimulate earlier formation of flowers lower in the plant.  These are much harder to remove than the terminal flowers that form on undisturbed plants.

Here is some stiltgrass pulled from the lawn after mowing.  You can see
 how low in the plant the stem flowers (cleistogamous) occur. These flowers
 need to be cut off for mowing to be really effective at eliminating stiltgrass.

Some folks have reported success with cutting the lawn really low in August, the beginning of flowering season.   Looking at some of the stiltgrass growing in the lawn, it looks like you would need to cut down to about an inch to reach those lower flowers.  I tried that in one section of my lawn that I have not otherwise treated and is mostly stiltgrass.  Next spring we'll see how that area compares to normally mown areas. 

After you manage to suppress the stiltgrass you need to get something else growing in its place.  The easiest option in the lawn is to overseed with a well adapted turf grass.  In the Mid-Atlantic the commercially available options are tall fescue blends for sun and fine fescues for shade.  In my rural setting I also have many other grasses growing in and around the lawn.  Some of the native species that are mixed in include path rush (Juncus tenuis), purple top (Tridens flavens), nimblewill (Muhlenbergia schreberi) and a variety of sedges.  While I encourage these to grow, they would be much happier if they were not mown on a regular basis.  Nimblewill, though, does seem to tolerate mowing pretty well.  

This is what nimblewill looks like in the lawn.  This warm season grass is
 not as 'pretty' as commercial turf grasses, but is is native and is well adapted to
 the climate here, even in this unseasonable hot and dry year.

I was planning on overseeding a large area in early fall, but here in Maryland it has been unseasonably hot and dry so I have been holding off seeding until the weather cools.  Getting the new seed established in the fall is critical to using most pre-emergents because they will suppress growth of most weeds planted in the spring. 

Another option to turf grasses is to convert from lawn to meadow or other types of plants.  Based on my meadow experience you should get rid of the stiltgrass before just adding other plants.  This can be done chemically, by solarizing (covering with plastic for  enough time to kill the stiltgrass seeds), or covering with cardboard or many layers of paper followed by mulch or clean soil and then planting on top.

In one shady area of lawn I have using timed mowing as the primary means of stiltgrass control.  I leave the area unmown from mid-June until mid-August.  At that time I'll pull out and remove the tallest grass and follow up with a low mowing.  After 3 years of this I am getting less stiltgrass, but it is still pretty thick.  One explanation is that there is a lot of stiltgrass in the surrounding area and the seeds may be coming in from there, either blown in or carried by the rain.  I did put down some pre-emergent in a small section of this area and there was no stiltgrass present there.  Mosses and perennial grasses seemed unaffected. 

The vegetable garden  In the garden one of the places stiltgrass flourishes is along the fence line.  It interlaces with the chicken wire and can be hard to remove completely.  This year I have been using a flame weeder to clear those areas.  This method is more effective early in the season when plants are smaller and more tender.  As weeds mature they have more moisture in their stems and leaves and are more difficult to kill with heat.  One caution with using a garden torch is not to expose soaker hoses or drip irrigation lines to the direct flame.  Unlike some weeds a soaker hose will not recover after being melted. 

Next steps: 

• Overseed with turf grass.  For next season  I am going after a large open area that is mostly mown stiltgrass.  I will use pre-emergent on this area in early spring assuming I can get the new seed established.
• Continue use of pre-emergent in lawn areas where stiltgrass is depleted.  While I have not been targeting it, the amount of hair cress, Cardamine hirsuta, a winter annual weed, seems to be decreasing in the treated areas as well.
• Continue testing pre-emergent in meadow, this time apply earlier in spring
• Expand areas in the woods where stiltgrass has been pulled.  Try and remember that the best strategy for removing invasive species is to clear a small area really well and then expand that area each year.  Also start in a less infested area and then move to higher density areas.  

Some Forgotten Native Mints

The Mints, Lamiaceae, are a large family of plants with about 40 genera appearing in eastern North America.  Native species that we commonly think of used as landscape plants include Beebalms (Monarda), Mountain mints (Pycnanthemum), giant hyssop (Agastache), Salvias and Obedient plants (Physostegia).  There are also the non-native species commonly used a culinary herbs like  thyme, oregano and the spearmint.  Common attributes of mints include tubular bilabiate (having two lips) flowers usually occurring in whorls or dense spikes, square stems and often aromatic foliage.  I recently wrote about the mountain mints that I have been growing and it got me to thinking of some of the smaller and less common (in the garden) native mints.

Here you can see the dense flower cluster of wild basil.   Blooming
continues from these throughout the summer months.

One of the wild mints that always surprises me when I spot it in the meadow is wild basil, Clinopodium vulgare, (formerly Satureja vulgaris).  Although the leaves and flowers are essentially unscented, this is made up for by the  clusters of pink flowers appear scattered throughout the tall grasses.  The stems are not particularly stiff, but they lean up against the taller grasses and meadow perennials like ironweed and wingstem (Verbesina alternafolia) allowing the flowers to reach up to 3 or 4 feet into the meadow matrix.  My plants bloom sporadically throughout the summer months.  I've also seen this plant growing alone in shady sites.  Without taller plants to lean on it grows about a foot tall on lax stems.
  

Here is some wild basil that is growing in shade and had been surround, until recently,
by Japanese stiltgrass. Note how the stems are reachng out to find more light.

The native range of wild basil is from eastern Canada to Tennessee and North Carolina.  Outside of that area plants are likely introductions from Europe.  On-line suppliers of native seed include Toadshade Farm and Prairie Moon Nursery (as Satureja vulgaris).

Pictured here is self-heal blooming in mid-July.  The flowering
 stalk grows from about 4 inches to a foot in height.

Self-heal or Heal-all, Prunella vulgaris, is found throughout the Northern hemisphere.  The North American variety (var. lanceolata) has somewhat narrower leaves than its European relative, which is also found scattered through the eastern parts of North America.  This perennial overwinters as a low mat of leaves that push up flowering stalks, 6-10 inches in mid-summer.  In my opinion these wouldn't work as a ground cover on their own, since they are attractive for only a few weeks to a month in summer.  But they would be a useful component in a mixed ground cover including violets, low sedges, spring ephemerals and the like.  One year it was growing densely in the vegetable garden so I thought I would treat it as a green mulch around some tomatoes.  Turns out the tomatoes did not do well surrounded by self heal.  I guess that there was too much competition and the tomatoes lost out.  
This plant is edible and can be added to salads.  Among its uses as an herbal remedy treatment of wounds and infections of the throat.   It is attractive to bees and butterflies and is a host plant for the clouded sulfur butterfly.  Seeds are available from several sources found on-line.  To get the North American variety you may need to check  and verify with the supplier where the seed is from. 

Here is Meehan's mint (circled) growing in dry shade.  Also present here
 are Virginia creeper (good) and Vinca minor (bad).  

Meehan's mint, Meehania cordata, is native to the Appalachian Mountains from western Pennsylvania to Tennessee and North Carolina.  It grows well in shady moist areas as a trailing vine that roots where leaf nodes contact the soil.  It can also handle dry shade, though it will be less vigorous.  In general appearance it is similar to the weedy invasive, ground ivy, Glechoma hederacea.  Meehan's mint has slightly larger and stiffer foliage and has no scent when crushed, unlike ground ivy.  Under favorable conditions it blooms in late spring with clusters of  inch long lavender blue flowers held on 6 inch long stems.  In this respect the floral display of Meehan's mint surpasses that of ground ivy.  It is recommended as a native substitute for exotic ground covers like ajuga and lamiums.

Mine is growing in dry shade and has not bloomed yet.  Follow this link to see it in bloom. When getting it established one needs to be careful about not confusing it with other similar, but non-native species like ground ivy and ajugas.  You can find Meehan's mint at nurseries specializing in native species or on-line nurseries, such as Izel Plants.

Mountain Mints

Mountain mints are members of the genus Pycnanthemum.  This translates from Greek as dense flower, an appropriate name for these pollinator favorites.  There are 19 species of mountain mints, all native to North America, found primarily the eastern half of the continent.  These plants have tight clusters of small white to purple tubular flowers that are very attractive to pollinating insects.  Many of these species have pleasantly mint-scented foliage.  The leaves can be used to make a mint flavored tea, although one species, short-toothed mountain mint, contains higher levels of a toxic terpenoid, pulegone, than the others.  They are also resistant to deer browsing, at least in part due to these terpenoid compounds.

This hoary mountain mint was growing along
a trail near the Potomac River.

Over the past couple of years I have added three species of mountain mints native to the Mid-Atlantic region.  The first one that I put in was hoary mountain mint, P. incanum.  (Incanum means gray.)  Its native habitat is listed as upland woods, which I interpreted as dappled shade with average moisture soil (mesic).  I have observed this species growing happily along some nearby trails.  

At home I planted it in a woodland edge, but it failed after about a year, probably due to too much shade and competition.    Where it has been successful is in open shade with dryish soil and less competition.  I expect it would be happier with a little more moisture and a little less shade. 

Note the grayish blush on the leaves and stems.  Also,
 the teeth on the leaf edge are small and widely separated.

Short-toothed mountain mint (P. muticum) is a species that I’ve had more success growing at home.  It seems happy growing in dappled shade in average well drained soils.  It needs more moisture than hoary mountain mint to excel.  Like hoary mountain mint it has a pleasant minty scent when disturbed and is very attractive to pollinators.  It is a more upright growing plant than hoary mountain mint.  On one site where I have it growing it is leaning over as it is reaching for the sun. 

Short-toothed mountain mint has white flowers and there are many short teeth along the leaf margins. 
Also the the leaves are broader in the center and thy are nearly sessile (no petiole).

The third species I have planted is slender mountain mint (P. tenuifolium).  This species, with its very narrow leaves, is well adapted for sunnier, drier locations.  Unlike the other two species discussed here, its foliage lacks a strong minty scent.  Even so I have not noticed any deer browsing on its foliage or flowers.  On the plus side it has relatively over-sized pink-tinged flowers that bloom from late spring to mid to late summer.  

The flowers of slender mountain mint come in dense clusters
making them look much larger than they are individually.

I got the slender mountain mint to plant opposite a threadleaf coreopsis (Coreopsis verticillata ‘Zagreb’) with the idea that the similar foliage would create a symmetrical design.  While the foliage of the two plants is similar, the laxer habit and bluer foliage of the mint gives a different impression than the tighter, upright form of the coreopsis.  This combination has worked out well for the pollinators. The coreopsis reach peak bloom in mid-June and the mountain mint took over in late June and is still going strong into mid-summer.

Coreopsis 'Zagreb' is on the left of the walk, slender mountain mint is on the right, behind the post. 
This combo doesn't look bad, but they are definitely different looking plants.

Overall I have been well pleased with my mountain mints: long-lasting minty foliage for me and lots of nectar-rich flowers for the pollinators.

Designing with Native Plants

Designing with native plants is not that different from designing with any other plant palette.  You still use basic design concepts, using the shapes, colors and textures of plants to create rhythm and flow in the landscape.  What is different is that your selection of plants is more focused on native species, ideally ones that are regionally or locally native.

Advantages

What you gain from using native species in your landscape is greater benefit to the nearby wildlife, better fit with the local ecology and character of the region, and, if your plant selection was right lower maintenance and increased sustainability.

There are North American native plants species that will grow under just about any landscape situation imaginable.  That doesn't mean that any North American plant will grow anywhere in North America.  Beyond the many geographic climate zones there are also differences in soil chemistry, texture, moisture, exposure to sunlight and competition both from other plants as well as animals.

By looking at nearby native plant communities you can get some inspiration about what to combine in your landscape.  At Mount Auburn Cemetery in Cambridge MA they created a meadow using many species of grasses and wildflowers native to the Northeast. 

This constructed 'Northeast Meadow' features showy goldenrod (Solidago speciosa),
little bluestem (Schizachyrium scoparium), New England blazing star (Liatric scariosa), hyssopleaf thoroughwort (Eupatorium hyssopifolium) and brown-eyed Susan (Rudbeckia triloba).

When I was designing a planting for a sloping path I selected some species that I observed along a nearby hiking trail in Maryland Heights.

Bottlebrush grass (Elymus hystrix) and clustered mountain mint
(Pycnanthemum muticum) are major components of this hillside garden.

While I stress about how you need to match plants to their ideal conditions, there are often surprising exceptions.  Test their adaptability by trying a plant or two in unusual locations, they just might catch hold.  This is why I like to use natives that produce a lot of seed, particularly native annuals.  The seed is able to spread around and find new places to grow, some of which will be a good fit.

This pink tickseed was originally planted in a near-by bed but found a better home when seed fell into a crack in the driveway.

Challenges

Some natives are generalists and are able to grow well under a wide variety of conditions.   Others are more specialized, having adapted to some very specific growing conditions.  Some of the frustration of working with natives is that while it is implied that they are adapted to grow in North America, a given native will not necessarily do well everywhere on the continent. 

Another factor to realize is that residential landscapes often have very different soil conditions than near-by natural areas.  Depending on where they are located around a building, light exposure and moisture levels can also be very different from undisturbed areas.  Newer construction areas often have compacted soils.  Many times the native top soil has been removed and replaced with soil from another location.

Reasons for failure of new plantings include competition from other plants, incorrect soil chemistry, texture or drainage, or missing  companion plants.  Also consider age of plants and the original conditions when they were planted.  Many shrubs growing in shade were planted when there was less competition both for light and root space.  Planting new specimens into an established wooded area is more challenging now than when the area was originally planted.  I have been fooled into planting new rhododendrons under established shade trees based on seeing mature shrubs in woodland settings.  In many cases, there is too much competition in the root zone for water and nutrients and too much shade cover for the new plants to get established.  Options here include opening up or raising the tree canopy, clearing a wider root zone (without damaging the existing trees), or  opting for more shade tolerant species.

Sometimes when I see native species dominating some harsh environmental conditions and I think, wow that could grow anywhere.  That is often faulty reasoning.  In many cases these plants excel because they have adapted to those conditions in specific ways to use those harsh conditions to their advantage to out compete other species.  

Rock harlequin will excel in thin rocky soils but does
 not compete well in normal soils against other plants.

One example is rock harlequin (Corydalis sempervirens) a short lived perennial that needs to reseed itself to maintain a garden presence. It's native to rocky slopes in the Northeast where there are shallow pockets of soil and exposure to full sun for a good portion of the day.  When planted in richer soil or 'better' conditions it often fails due to competition from other plants. 

Almost all plants in nature grow in a community of some sort.  There are a few  species that require a host plant to help them grow and develop.  Indian paint brush (Castilleja sp.) tap into the roots of neighboring plants, such as little bluestem or penstemons, for nourishment.  False foxgloves (Aureolaria sp.) are partially parasitic on the roots of oak trees.  And , like many members of the pea family, Texas bluebonnets (Lupinus texensis and sp.) do better when there are specific soil bacteria present to help them fix nitrogen. 

Texas bluebonnets are winter annuals that blanket open fields with their iconic blue and white flowers in early spring.  They are well adapted to the calcareous soils with the assistance of a soil bacteria.  Performance in other regions is erratic. 

Plant Selection and Sources

The nature of native plants are that they are native to particular areas of the country based on climate, soil chemistry and evolutionary history. As such there are very few 'nationally native' plants, nor should there be.  If you search the garden centers you can often find sections devoted to native plants.  The nice thing about many commercially available native plants, though there may not be many of them, is that most have been selected to be commercially viable, that is they work in many residential situations and are fairly robust.  We need to expand the offerings by asking for more of these plants.  American Beauties is one program based in the Northeast that is supplying a variety of native species.  There are also a number of native plant suppliers that you can find on the web.   Izel Plants is a clearing house for a number of native plant nurseries primarily in the Eastern US and has an extensive catalog of native species.  The Plant Native link below also has listings of native plant nurseries by state.   You can also search the web for nurseries in your region that specialize in native plants. 

To help with the selection of which species to use there are a number of websites that allow you to search for plants based on the site conditions.  You can find plant search websites for a given area by using search terms like 'Native Plant Database for  '  My favorite site to search is from the Wildflower Center.  It allow you to search by where a plant is native as well as specific growing conditions and plant attributes such as size and bloom color.  Plant Native is another good site.  While the plant lists are smaller, the plants listed are mostly commercially available.  Missouri Botanical Garden has an excellent search platform, but it is not solely native species.

Strategies for Designing with Native Species

• Try to match the preferred conditions/habitats of a new plant to your local conditions (much easier than trying to match your conditions to those of a given plant).
• Start small, when in doubt.  Before doing a massive planting put in a couple of plants as a test to see if they survive.
• Try a new species in a couple of different locations to see where it grows well. 
• Don't just drop a new plant into an established bed.  Clear some area to allow for roots to get established without competition.  Also open up the canopy to let in some light.  Water well, but don't feed perennials, shrubs or trees until the roots are established (about one growing season).
• Build a plant community by learning about which plants grow together in nature.
• When starting perennials from seedlings, like you get with liners or sizes one quart or smaller, it will take as many as three seasons for them to reach their full glory.  The adage 'sleep, creep, then leap' really does hold true when start from small specimens.