Wednesday, May 16, 2018

Stiltgrass progress - May 2018


It would be nice if the growth of Japanese stiltgrass, Microstegium vimineum, would wait until we were done dealing with garlic mustard for just a little while, but I have seen signs of it germinating here (Central Maryland) in early May.  So now is a good time to take a look at how some of the steps I've been taking to get rid of this invasive grass are doing.
A snapshot of one of the lawn areas.  In the foreground is
Zoysia grass, still in the process of greening up. 
This grass grows thickly and excludes many weeds.  Further
on are areas where Japanese stiltgrass has infested the lawn.

This is what a shady, unmanaged area looks like.  The arrows are
pointing to areas with a high density of stiltgrass seedlings. 
Also present are plantain, dandelions and violets.
In areas where I have not been actively managing Japanese stiltgrass I am seeing dense patches of seedlings, mostly in the gaps between clumps of grass and other lawn plants.  This area has been overseeded with a 'no-mow' fescue, but otherwise gets no special treatment.
Vigorous raking does seem to have reduced the number of stiltgrass seedlings in this early period of germination.  This practice will be continued here to see if the lawn can grow back together to exclude future invasions.  This method takes a lot of work, especially if I were to expand beyond the 100 sf test area.  Left alone even these few seedlings would expand to fill in the gaps in the lawn and produce a significant crop of seeds.

In this area I have been vigorously raking the lawn in mid-
 to late-summer for the past 2 years to remove established stilgrass plants
to try to reduce the number of seed produced.  The arrows (3) point
 to small clusters of stiltgrass.

In the areas treated with the pre-emergent herbicide, Dithiopyr ('Dimension'), I've noticed little to no seedlings of stiltgrass, or other plants for that matter.  Reflecting back on the timing, I should have waited until mid-April to apply this material so as to let some of the cool season grasses get started.  But it's hard to predict when a warm snap will come along and mess everything up. 

I
This area was treated with a pre-emergent herbicide, dithiopyr ('Dimension') at the
end of March.  I was not able to spot any stiltgrass seedlings in this area. 
Other plants here are clover, Indian strawberry, and purple lamium.
One of the most dramatic results was where I used a lawn torch to burn off all the surface vegetation in late summer last year when the stiltgrass was in flower.  A few perennial grass plants bounced back after a week, but it was necessary to reseed the area to provide cover for the soil.  As I mentioned awhile back burning seem to be most effective in the fall prior to the seed ripening/dispersal.  Burning also eliminates the cleistogamous seeds found low on the stem.  Burning after seed is dispersed is too late and spring burning just opens the group to germination from the existing seed bank (see this report from the Forest Service.)  The burned area seems completely free of stiltgass, as well as some other weeds while the contol area is dense with stiltgrass seedlings.

 
Here is a comparison of an area that I burned with a yard torch in late summer
last year (right side) with an control patch where nothing was done. 
The burned are was overseeded with a tall fescue blend, nothing for the control. 
Arrows indicate dense patches of stiltgrass seedlings.
  
While it is too early to be certain, it appears that there is progress being made against stiltgrass in my lawn.  The pre-emergent seems to be working at this early date.  The downside is that it also affects desirable seedlings.  As indicated on the label, it is best used on established lawns.  There is a possibility that stiltgrass will reemerge in mid-summer after the pre-emergent breaks down (about 3 months after application).  Burning seems to be an effective non-chemical approach.  It looks bad for a little while, but there are not residual effects to worry about.  Since stiltgrass seed can remain viable for 5 years in the soil I will need to stay with this for some time to come.


Wednesday, April 25, 2018

Preping the Garden

Last year's garden did not do so well.  On reflection there are a number of reasons, some of which are in my control.  Others, not so much.  To do well all plants need sunlight, nutrients and water.  And in my location, protection from pests.  In my mind I was providing all those, but in practice I was coming up short.

Here's the garden half-way through: last year's growth raked out, garden mowed low,
3 beds weeded with scuffle-hoe and rake.  Note the log pile just beyond fence,
all that remains of the big box elder, Acer negundo.

I have been adding compost, shredded leaves and a little organic fertilizer in the past. Last spring I sent samples for a soil test and learned that levels of most nutrients were too high: phosphorus, potassium, calcium and magnesium.  On the positive side, there was an increase in the organic content and cation exchange capacity (a measure of fertility). So this year I will only add an organic nitrogen fertilizer to the soil.  Of the organic choices that had minimal phosphorus and potassium I considered soybean meal and feather meal, both with about 7% nitrogen.  I opted for the soybean meal because I could by it from the feed store for about 25 cents a pound.  One warning with the soybean meal that I read was that it could inhibit the germination of small seeds.  So I'm not using that in the beds where I am planting lettuce, collards, chard or arugula.  I'm hoping that the beans, peas, spinach and others will be OK.  I got all the fertilizer down now (mid-April) and that should give it some time to be digested by the soil biota and have food ready for the bulk or the planting in mid-May.

As far as sunlight goes, I thought that I had good exposure.  That may have been the case 5 years ago, but the trees have been growing taller and eventually cutting a couple of hours of direct sun from the garden area.  While I hate to remove trees, there was a big box elder just south of the garden that appeared to be causing most of the trouble.  Since box elders are pretty common here, it was only with a little difficulty to say good-bye to that tree.

We usually have good rain here and I have a soaker hose to put in place for supplemental water.  So for moisture, I should be in good shape.

The last problem is the critters.  Every time I think I have a solution, they seem to adapt, or another problem crops up.  The double fencing seems to keep the deer at bay and the buried chicken wire slows the ground hog down; however I think it can still climb over the chicken wire when it really wants to.  Last year many seedlings were getting eaten and I'm not sure who to blame.  This year I have a motion activated trail camera to use so I can get a clue as to what is getting into the garden.  I am also expecting that the thicker layers of wood chip mulch will make it more obvious where any burrowing is taking place.

Other garden preparations:
I cut back the long tips of the wild blackberries growing on the outer fence. 
This improves fruit quality and gives more space to move around.

I've allowed wild blackberries to grow along the outer fence of the garden.  This re-enforces that area against deer.  I've read that by pruning the side branches to 4-8 leaf buds the fruit quality is improved.  I've been doing that for a couple of years now and it seems to be true.  The 'managed' wild blackberries have larger, sweeter fruits than the unmanaged plants nearby.



Rather than cutting to the ground I left 1-2' of the hollow
Monarda stems as potential bee nesting habitat.

Another plant growing along the fence line is wild bergamot, Monarda fistulosa.  These grow up about 4' and are very attractive to bees in early to mid-summer.  The hollow stems can provide nesting sites for small bees, like mason and leaf-cutter bees.  Since these bees build their nests in summer and develop there through the fall and winter, these stems need to be left intact for over a year.  When I did the garden clean-up I cut most of these stems to leave 1-2' intact.  These old stems will disappear into the new growth by the end of spring.  I just need to remember to leave them alone for the next year. 

As a result of a lot of tree work done here this spring, I have a large supply of wood chips.  This year was therefore the year to replenish the garden paths with fresh chips.  Many folks don't like to use fresh chips in the garden because they take up nitrogen from the soil as they decompose.  Since I want to suppress growth on the paths and garden perimeter, these fresh chips are just the thing to use.  (This loss of nitrogen from the soil only occurs where the mulch touches the soil and does not significantly affect the root zone unless the wood mulch is dug into the soil.)

The gardens all ready for plants:  freshly weeded, fertilized and mulched. 
I ran out of mulch for the last two beds...we'll call this an experiment. 
The remaining greenery are mostly native perennials like
beebalm and coneflowers to attract pollinators.
One new thing I am trying this year is to put down a wheat straw mulch over the bare soil.  This should help with moisture retention and reduce the number of weeds, or at least those from new seeds being blown into the garden.  I am expecting that wheat straw is much lower in weed seeds than is regular hay.

Now it's (past) time to plant those peas!!!



Monday, March 26, 2018

The Forsythia are in bloom, now it's time to...


The blooming of Forsythia is a signal to begin a number of outdoor tasks.  It signals a good time to apply preemergent herbicides for control of summer annual weeds.  I'm giving this a go this year as another tool to get rid of Japanese stiltgrass, Mircostegium vimineum, from my property.  I've been making progress in the woods where I have been pulling it out in July and August as it is getting tall.  Getting it out of the lawn is another matter.  


It's the end of March, and although the Forsythia started blooming
at first in January, I think they are doing it for real now.
There, repeated mowings keep it short and actually induce early seed formation in the lower stems.  I have been raking/combing it out of the lawn in a few areas but that does not seem very effective.  It seems that while I remove a lot of the weed, any remaining stiltgrass just expands to fill in the gaps.  So while I prefer to avoid the used of synthetics, I've tried going it alone for a couple of years and now I need some help.  

Many of the common preemergent herbicides used for crab grass control have been found to be effective on stiltgrass when applied prior to seed germination.  Preemergents that have been shown to be effective include Dithiopyr ('Dimension'), Pendamethalin ('Pendulum'), Prodiamine ('Halts') and Trifluralin ('Preen Weed Preventer').  One of the challenges is finding a preemergent that does not come with added fertilizer.  In my case I do fertilization in the fall, since I am growing mostly cool season grasses, particularly fine fescues, Festuca rubra cultivars.  Fine fescues have low fertilizer demand and I see no good reason to apply fertilizer at a time when weeds are about to take off. The product I found contained only Dithopyr, no excess fertilizer.



Hairy Cress is a winter annual weed that has been taking over here.  Last year I mowed
it early before much of it started producing seed.  This year I'm hoping
 to get some added help from the preemergent herbicide.

As an added bonus this may help control the hairy bittercress, Cardamine hirsuta, that is growing in the lawn.  This weed is a winter annual, sprouting in fall and again in early spring.  While it dies back by mid-spring, this creates gaps in the turf that provides space for the stiltgrass to fill in. 

Dithopyr works by interfering with development of new roots, after seeds have germinated.  Perhaps I should have waited a little longer to put this down in order to allow the existing grasses to get further along, but I didn't want to forget. We'll see how all this works out later in the summer when I can compare treated and non-treat areas for amount of stiltgrass.  Check out this earlier post for some things I tried last fall. 


Sunday, January 28, 2018

Replacements for Nandina and other learnings

Recently I wrote an article for Houzz on plants to use instead of Nandina domestica, aka Heavenly Bamboo or Sacred Bamboo.  This overused Asian species is adaptable to a wide range of growing conditions in USDA zones 7-9 and has reached invasive status in the Southeastern US.  In Maryland it is listed as a Tier 2 invasive plant meaning that, while it can still be sold in Maryland, it must be accompanied by signage stating that this is problematic species. 



In addition to its invasive characteristics, the bright red berries so prominent in winter are actually quite toxic to over-wintering birds.  The cedar waxwing is particularly susceptible due to their feeding behavior.  Blue Jays and Mocking birds are examples of other species that are at risk from this shrub.

You can read more about the toxicity of Nandina berries to birds in this post from Audubon Arkansas. You can mitigate this problem somewhat by planting more plants that bear fruit late in the season, particularly native species; but, you should not consider Nandinas as wildlife-friendly plants. If you want to use Nandinas for aesthetic purposes consider cultivars that do not produce berries such as 'Nana', 'Nana Purpurea', 'Atropurpurea Nana', or 'Gulf Stream.' These non-bearing cultivars are also less likely to spread outside the garden.

One of the species that I recommended in this article is Oregon Grape, Mahonia aquifolium, and other members of the genus.  This broadleaf evergreen shrub is native to the Pacific Northwest, but is also found growing wild in some eastern states, most likely as a garden escapee.  I thought I had some growing in my backyard, too.  While researching this species I discovered that what I had was, in fact, Mahonia bealei, Leatherleaf Mahonia.  This species, originally from western China, is listed as invasive in many of the same states as Nandina.   



Here are two Leathrleaf Mahonia growing in a clump in late January. 
This species of shrub typically grows 4-10' in height,
compared to 3-6' for the Northwest native Oregon grape.
The bright yellow flowers of Leatherleaf Mahonia bloom in late winter to early spring
on clusters of terminal racemes.  This species can be distinguished from Oregon Grape,
M. aquifolium, by the number of leaflets, 9-15 vs. 5-9, for Oregon grape. 
Also the leaf color of leatherleaf mahonia is a dull bluish green compared to
the shinier dark green leaves of Oregon grape.

Learning that what I thought was Oregon Grape was actually a non-native species with invasive tendencies, I've decided to replace it with species native to this area.  Even before this revelation I was considering replacing it with a more appropriate East Coast species.  I would like to have an evergreen shrub that likes moist soils and open shade.  Looking at my list of Nandina replacements for inspiration, I think I will go with Inkberry Holly, Ilex glabra, as the replacement. As with most hollies I will need both a male and a female plant to get berries for the birds.  Fortunately there are both male and female cultivars available in the nursery trade so I will be able to start an inkberry family without too much trouble.  As the male I will go with 'Nordic', a fairly compact species.  There are more choices for the female.  I would like them to grow to about 6 feet, so I have a choice of 'Compacta', 'Densa' or 'Nigra'.

This inkberry is part of a new parking lot planting at a local library
that features mostly native species.  It does well in part to full sunlight. 
My site may be on the shady side, but that may encourage
a more open form that I would like for my particular application.



Wednesday, January 10, 2018

Using Bare Root Plants

Over the 5 years or so that I've been here in Pleasant Valley (Zone 6b) I've been augmenting our grounds with more native species.  In order to get some of the species I wanted I've been getting more bare root plants than in the past.  What I like about them is that you can find many species that are not available in containers and that they are much less expensive, averaging about 1/3 the cost of the same plant in a container.  This lower cost is due in part to the lower costs of shipping, only the plant without the soil, and to lower production costs at the supplier.  The down side is that these plants are only available when they are dormant and that they need to be planted while it is still pretty chilly out, either in late fall or very early spring. So right now (January) is a great time to get in an order, in time for early spring planting.

I've had mixed success with these bare root plants.  Reasons for failure include not planting them in the right place, competition from existing plantings, deer browsing and some poor technique.   I won't go into the steps of planting bare root plants, they often come with detailed care and planting instructions.  You can also find instructions on the web. 

Here are some things I've learned from my experiences:

Get plants in the ground quickly.  If possible get them in the ground within a day or two of when they arrive.  While you can keep them in cool storage for a time as long as the roots stay moist, or you can heel them in, by laying them in a shallow hole and covering the roots with moist soil.  I seem to be having better results with plants that I put in place quickly.  It is important to get plants in the ground while they are still dormant.  This way roots can get in good contact with the soil before the buds open and put a greater stress on the plant.  I have planted bare root stock in both late fall and early spring.

This Canaan fir has been in the ground for about 2.5 years. 
It started at about 6 inches.  The chicken wire and steel posts help
protect it from male deer who will rub off the branches
as they clean their antlers.
Get good soil contact with the roots.  When planting in the garden make sure that soil is well packed around the roots and spread the roots out in the hole as you layer in the soil.  What I have been doing lately is carefully spreading out the roots as I have been adding in the soil.  After about half of the hole is filled I fill the hole with water and let it settle.  This removes air pockets and improves soil contact with the roots.  I continue to fill in around the plant with soil, continuing to spread out the roots, followed by another through watering. 

Plants in pots need time to develop a good root system.  For bare root plants that I haven't had time to plant, I've potted up with container mix, watered them well and left them in a cool protected location.  Only about half of the plants survive until the weather warms up.  Not a particularly good record.  The survival rate of these potted up plants after transplanting has not been great either.  What I believe to be happening is that the roots have not had a chance to develop while in the pot and there is too much damage done to these weak roots when they are transplanted into the garden.  I've had better success with plants that I've allowed to grow in the pot for a full season before going out in the yard.

Protect plants from critters and competition.  I've lost a number of young plants to deer browse, so now I put a little chicken wire cage around most of my new plants.  I've also lost a number that have been shaded out by surrounding vegetation.  When planting in mid-fall or early spring it is not obvious how much crowding there will be come June and July.  I need to remember that these are still little plants and they are easily over-shadowed by larger established vegetation.  Like any new plant, bare root plants need extra water while they are getting established.  I also tie a fluorescent pink ribbon around each new plant so that I can locate them more easily when clearing out the competition.

Close examination of this Juneberry shows that the leaf buds
are still plump and healthy looking.  A good sign
that it will survive the winter.  The pink ribbon helps me keep
track of these new additions in the landscape.

Here are some of the species I've worked with:
Here is the Twinleaf in bloom.  This is one of the first bare root plants
I put in.  It's now 4 years old.

Perennials:  Celendine poppy (Stylophorum diphyllum), Christmas fern (Polystichum acrostichoides), Merrybells (Uvularia sessilifolia), Twin leaf (Jeffersonia diphylla),and Jack in the Pulpit (Arisaema triphyllum) have performed quite well.   Mayapple (Podophylum peltatum) and  Large-flowered bellwort (Uvularia grandifolium) are in dryish soils and have been struggling.  The wild ginger (Asarum canadense) was planted in a very challenging location, under an English walnut and surrounded by vinca, and has faded away. Alleghany pachysandra (Pachysandra procumbens) was planted in November in a dry shady location, so we'll see how that works.

Shrubs:  Black chokeberry (Aronia melanocarpa),  Gray dogwood (Cornus racemosa),  American hazelnut (Corylus americana), Witchhazel (Hamamelis virginiana), Spicebush (Lindera benzoin),  Chokecherry (Prunus virginiana),  Smooth sumac (Rhus glabra), Red elderberry (Sambucus pubens),  and Meadowsweet (Spiraea alba v. latifolia).  The meadowsweet and hazelnuts have been the most successful at getting established.  Smooth sumac has suffered from both deer browse and being over shadowed by other aggressive plants.  The red elderberries and witchhazel which did not make it were in very shady spots.  The chokecherries were potted up when they got here and only 2 of the 6 survived.  Those 2 were planted out 3 months later.  Soon we'll see how they made it through their first winter.   

This American hazelnut has been in the ground
for about a year now.  In the inset you can see the swollen leaf bud
that indicates that this branch is still alive.


Trees:   Canaan fir (Abies balsamea v. phanerolepis),  Concolor fir (Abies concolor),  Juneberry (Amelanchier canadensis),  Redbud (Cercis canadensis), Red cedar (Juniperus virginiana), Tupelo (Nyssa sylvatica),  Virginia pine (Pinus virginiana), American plum (Prunus americana), and  Douglas fir (Pseudotsuga menziesii) .   The best performers of this group are the tupelo and the Douglas and Canaan firs.  Ones that have not worked out here are the Virginia pine (wrong soil type here), Redbud (location had too much shade from competition), Red cedar  and  the Concolor fir (uncertain).  The American plum was just planted this fall, so the jury is out, but they look OK so far. 

Thursday, October 5, 2017

Progress on Japanese Stiltgrass Removal - 2017

My 4 year long battle with Japanese stiltgrass, Microstegium vimineum, is continuing and it must be a continuing fight to remove this invasive grass from my property.  Since this is an annual grass the goals are to keep it from producing a new crop of seed and to eventually deplete the seed bank so that it won't crop up again from older seed.  Since this grass is all around I will need to take the fight to the neighborhood and beyond.  This will be easier if I can demonstrate to  other that this is a battle that is worth fighting.

One approach to Japanese stiltgrass removal is to nuke the site with round-up or a grass selective herbicide.  Despite it being effective on the current year's growth, this would still be a multiyear approach to deplete the seed bank.  I'd rather not kill everything because I have a number of interesting plants that I want to keep and I am generally opposed to the indiscriminate use of herbicides or pesticides. 

The key to non-toxic approach to stiltgrass removal is good timing.  Pulling the grass in late summer as the flowers are forming (late July to early September in Maryland) is the best time to concentrate your efforts.  Early season pulling helps, but if some plants remain they will expand to fill the void and you will need to return to pull again.  Stiltgrass pulled before seed has formed can be composted, though I usually segregate it from the rest of my garden scraps just in case.   Any grass pulled after flowering should be bagged or at least segregated and covered so that seed can not escape.
Here's a woodland edge area in 2013 when I started pulling/whacking stiltgrass
In 2014 coverage is not as dense, but still dominant.
In 2015 other plants are showing up.  Also I had seeded in some Virginia rye in 2014.
Now in 2017 stiltgrass is no longer dominant.  In the foreground is
Virginia rye, Elymus virginicus, drying out after seeds have matured.  

 The photos above show the progress that has been made over 4 years.  For the first two years this site was weed whacked to near ground level and then raked out.  As the stiltgrass density dropped I switched over to hand raking and pulling for the past two years.  These methods were more selective and allowed me to avoid the more desirable plants that were coming back in.


Mature Japanese stiltgrass, note the
location of the cleistogamous flowers.
In lawns, mowing stiltgrass is done to control its spread.  Unfortunately stilt grass has the ability to form cleistogamous flowers near the base of the stem.  These flowers are enclosed in a leaf sheath about an inch off the ground and can survive most mowings.  It has been reported that these flowers mature earlier in stiltgrass in regularly mown lawns.  To address this Russ Anderson, a West Virginia forester has suggested allowing stiltgrass to grow freely through July and then mow it closely to the ground in August as the flowers begin to develop.  The expectation is that there will be fewer cleistogamous flowers and by cutting it back late in the season there is not time enough for the grass to regrow.  I have been doing a variation of this in an isolated area where I am growing fine fescue.  Instead of mowing, I use a manual grass whip.  This rips out the stiltgrass and leaves more of the fine straight blades of the fescue intact.  After doing this for two years the amount of stiltgrass in the area has decreased, but I still have a few years to go.  

Another technique that I have been using  to remove stiltgrass from the lawn is to briskly rake the lawn after a rain to try and catch the lateral stems (stolons) of the stiltgrass.  Using a spring or bamboo rake does tear out a lot of stiltgrass, but it also tears up the soil and can damage the bunch and perennial grasses as well.  I also found that after doing this in early July, even though I removed a great deal of stiltgrass, much of it had regrown to fill the gaps in the lawn.  Inspection of the stiltgrass at this time did not show evidence of the cleistigomous flowers. 

This area was raked over with a steel garden rake.  Nearly all this debris is stiltgrass.

What appears to have worked better is a stiff steel garden or bow rake that is pulled along the surface of the ground.  It catches and pulls out the stolons of the stiltgrass and since the action is not so vigorous, most of the other bunching grass are left intact.  I did this in mid-September so there is not enough time for the stiltgrass to regrow.  Even though the soil was dry, the stiltgrass pulled out easily.  Inspection of the stems showed that there were some cleistogamous flowers forming at this time.



Areas that are blackened were burned with the torch (next to watering can). 
I kept a full watering can nearby just in case the fire got out of hand (it didn't).  I left a small area
in the middle un-burned as a 'control group'.
These mechanical methods are helping reduce the number of stiltgrass plants in the lawn but there are still a number that escape the raking and pulling.  A new approach that I am trying out this year is fire.  Burning stands of stiltgrass is not effective early in the season while new plants are still germinating, or in the off season when plants are already dead (stiltgrass seed is relatively fire resistant).  However, burning in late summer as the stiltgrass is beginning to flower may be a way to successfully battle a stiltgrass invasion.  This method was suggested to me by Joene Hendry, who writes the blog  Joene's Garden.  The process I am trying is to first mow the area close to the ground (about an inch), then allow a day or two for the grass to dry out.  Next use a garden torch to burn the remaining stems, this should get at those hidden flowers.  While this may seem extreme, any perennial  grasses with good root systems will bounce back in a week or two, but the stiltgass is not able to recover.   I did try burning without mowing first, but stiltgrass holds a lot of moisture and it takes a long time to completely burn up such a moist plant.  Mown plants, without a lot of leaves, were quickly burned up.

Another element of stiltgrass removal is to fill in the gaps with desirable vegetation.  Since I am located in the cool season grass zone I have been using a fine fescue blend (like Eco-lawn) in the shadier areas and tall fescue blends in the sunnier spots.  I do have some zoysia grass growing in the sunnier spots.  This warm season grass grows thickly and excludes most of the stiltgrass.  It's unfortunate that there are not more native options for turf in this area (although red fescue, Festuca rubra, is technically a native species).  By avoiding the use of broad spectrum herbicides I do allow the native sedges, violets and other species a chance to repopulate.

I did get an early start over-seeding this fall and I hope to have the new plants established before it gets too cold.  If these desired grasses get established I will experiment with some pre-emergent herbicides.  These act by  interfering with root development after seed germination.  These are particularly effective on annual species such as Japanese stiltgrass and crabgrass.   I imagine a year without stiltgrass competition should help develop a thicker lawn. 

Saturday, July 1, 2017

Red, White and Blue for the Fourth and other times, too

Happy Fourth Of July!  When I think of the 4th it's all about red, white and blue.  In the garden these colors are not usually used together, unless you are doing a theme planting or a flower arrangement.  Occasionally it happens, though, by accident.

This mostly native arrangement has 'Annabelle' Hydrangea for white,
Monarda didyma and non-native Salvia splendens for red, and the blue
 is supplied by Campanulastrum americana and Salvia farinacea 'Victoria blue'.
The green fireworks are bottlebrush grass, Elymus hystrix.
While I didn't plan this color scheme, this combination of
blue flag iris, Iris versicolor, and the red and white striped flowers
of myrtle-leaf mountain laurel, Kalmia latifolia 'Minuet'
made a pretty nice display in late May. 
Here are some North American native plants that can supply you with red white and blue flowers for each season of the year.

Reds:
Scarlet sage is not hardy here so I grow it as an annual.
However, its seed will overwinter with a little protection
 In picking out these plants I looked for true reds rather than the many pinks and purples that are out there.  Roughly in the order of bloom from spring to fall  there is red trillium (Trillium erectum), wild columbine (Aquilegia canadensis), Indian pinks (Spegelia marilandica), fire pink (Silene virginica), red beebalm (Monarda didyma), various red salvias (Salvia ssp.), standing sypress (Ipomopsis rubra), turkscap (Malvaviscus arboreus), scarlet  rosemallow (Hibiscus coccineus) and cardinal flower (Lobelia cardinalis).
Cardinal flower makes a strong statement in late summer in sunny moist locations
White:
The pure white flowers of bloodroot are one
of my favorites in early spring.
There seems to always be something white in bloom. Here are 10 native plants with white flowers roughly in order of appearance:  Bloodroot (Sanguinaria canadensis), Phlox (all species have some white forms blooming from early spring to late summer), beardtongue (Penstemon digitalis), elderberry (Sambucus canadensis), hydrangea (H. arborescens and quercifolia), summersweet (Clethra alnifolia), swamp rosemallow (Hibiscus moscheutos, often with a scarlet center), tall snakeroot (Ageratina altissima), white turtlehead (Chelone glabra) and various asters.
Elderberry has large flat flower clusters
for nearly a month in late spring.


Blue:
There are also native blue flowers throughout the growing season.  These plants tend to prefer shady locations.  Also their blue flowers show better in part shade than they do in full sun.  Many of the blues tend toward lavender or purple, I've tried to select more mid-range blues.  Here are a few, again in order of bloom:
Virginia bluebells carpet moist ground in early spring.
Virginia bluebells (Mertensia virginica), Jacob's ladder (Polemonium reptans), Ohio spiderwort (Tradescantia ohioensis), blue flag iris (Iris virginiana), American bellflower (Campanulastrum americanum), gayfeather (Liatris spp.), mealycup sage (Salvia farinacea), blue mistflower (Conoclinum coelestinum), great blue lobelia (Lobelia siphilitica) and various blue asters.

This smooth aster is one of the bluer (less purple) native asters in the eastern US.
(Should be Syphyotrichum laeve, sorry)

There are many other red, white and blue blooming natives out there and I would appreciate hearing what your favorites are.  And again, Happy 4th!!!