Native Plant Wish List for 2014

With a new planting season approaching I am planning on continuing my crusade to replace  the invasive species with native, mostly indigenous, plants.  I have another round of brush clearing to do this winter, especially the removal of some Autumn Olive tree/shrubs.  I am also looking to reduce the number of Butterfly bushes and Forsythia on the property and replace them with higher value native shrubs. 

Over Christmas I took the time to finish reading Designing Gardens with Flora of the American East, by Carolyn Summers.   The chapter on 'showy substitutes for invasive plants' was very inspirational in making up my plant list for this season.  This book is an excellent resource for anyone interested in designing native plant gardens.  There is sound reasoning behind each of the recommendations in this book.  I found this to be  much more useful than just a list of what should or should not be done when designing a garden or landscape.   To enhance the wildlife value of our property I am trying to  use a combination of plants that have something in bloom throughout the season for the pollinators as well as berries and fruits for the birds and small mammals.

Anyway, here's a list of my target plants for 2014:

Pussy Willow, Salix discolor.  I was surprised that this is a native species.  I is used so commonly in early spring decor that I figured it had to be imported.  The catkins swell in very early spring, first as white, silky buds, then opening to reveal either yellow (male) or greenish (female) flowers.  Pussy Willows are dioecous, male and female flowers are borne on separate plants.  My plan is to use the pussy willows as replacements for Forsythia.  The color intensity will be much less, but the wildlife value will be so much higher with the willow.  For all its flowers, I have seen very few bees visiting a forsythia in bloom.    Pussy Willows like full to part sun and prefer moist soils but will tolerate some dryness.  They are larval hosts for Viceroy and Mourning Cloak butterflies and they tolerate deer.  

I'm not sure of the exact species.  This photo is from the end of March in Boston.

I took this photo of a shrubby willow at the Arnold Arboretum about 5 years ago.  I did not record the name at the time.  As I was trying to find out more info about it, I went to the arboretum's web site and found that they have actually made an Internet accessible map of their plantings.  Using that map and my memory of where I took the photo, the willow in question is either the native Bebb's Willow, S. bebbiana, or an introduced Black Willow, S. gracilistyla 'Melanostachys'.  Based on the light color of the catkins, I guess that it's the former.

Another substitute for Forsythia is Spicebush, Lindera benzoin.  Its flowers impart a yellow haze to the forest understory about the same time as the Forsythia are in bloom.   It grows better in shadier situations than either Pussy Willow or Forsythia. 

For a partly shady area I would like to try replacing the Forsythia with Red Osier Dogwood, Cornus sericea.  This plant is in bloom from mid-late May and follows up with nutritious berries in mid-late summer.   Besides the flowers and fruits this dogwood also has purplish fall foliage and red-colored stems in winter, features definitely lacking in the one-trick pony, Forsythia.  Species plants can get large (6-10') but there are compact cultivars like 'Isanti' and 'Arctic Fire'.  A big problem with dogwood is that deer find most of the plant pretty tasty, but I have seen large plantings doing well along the roadsides.  This dogwood serves as the larval host for the Spring Azure butterfly.

This 'Isanti' cultivar is in full bloom at the end of May and should grow to about 6 feet.
Cutting back the older growth each year will keep the size down
and give more new red stems in the winter.

As far as replacing the Butterfly Bushes, Buddleia davidii, a multi-shrub approach may be needed.  Butterfly Bush has a long period of bloom and is very attractive to pollinators.  But it's like candy.  The plant does not act as a host for any native insects.  Thus, as it displaces native species, it excludes useful host plants, and degrades the habitat value of the garden.
 

The seed heads of Sumac make them easy to spot.  Not sure which species this is.
The stems of R. glabra are smooth, while those of R. typhina are hairy.

For the early part of the summer I am looking to Smooth Sumac, Rhus glabra.  This is also a common roadside plant, but not so common in the nursery trade.  It's chartreuse panicles do not stand out to humans, but they do to butterflies.  What is most noticeable in this shrub is the scarlet fall foliage and the deep red berries through the fall and winter.  It grows to about 15 feet, similar to many of the mature butterfly bushes around here. The larvae of the Hairstreak butterfly use Sumac as host plants.

For  the second part of the season I will put in some American Elder, Sambucas nigra ssp. canadensis (often S. canadensis).  American Elder likes medium to moist soils and part to full sunshine.  I have seen this growing in roadside ditches covered  with white umbels in the middle of summer.  Dark, palatable berries follow in early fall.   This shrub does not have a neat compact form, but neither do most forms of Butterfly Bush.  I am somewhat concerned about deer browsing on the young plants, so some protection will be needed. 

This native Spiraea blooms throughout the summer
and is a magnet for bees.

Other shrubs that provide mid and late summer flowers which  I put in last year include dense St. John's Wort, Hypericum densiflorum, and Meadowsweet, Spiraea alba var. latifolia (this one blooms all summer long).

In the areas where I have cut down the Autumn Olive, Elaeagnus umbellata, I am looking for native plants to provide lots of mid-summer  flowers, a large crop of fruits, and fairly dense branching to provide cover for birds.  Cockspur Hawthorn, Crataegus crus-galli, looks to be a good fit.  It blooms through mid-June and has lots of berries from late summer into winter.  It has dense horizontal branching and long thorn that provide a lot of protection for birds.  (For use closer to people there is a naturally thornless variety, var. inermis.) 

I would also consider Chokecherry, Prunus virginiana, while blooming earlier, it is faster growing and has fewer disease problems.  Chokecherry lacks the thorns of Hawthorn, but can form a thicket-like colony.  Looking in Douglas Tallamy's book Bringing Nature Home,  the cherries are near the top of the list as far as their ability to support butterfly species.  Hawthorns come in 12th, both way ahead of an invasive species like Elaeagnus. 

'Blue Muffin' is noted for it's sapphire berries,
as long as there is another Arrowwood around for pollination.

The other shrub that I will be putting in place of the olives is Arrowwood Viburnum, Viburnum dentatum.   These bloom in late May through mid-June and produce dark blue berries from late summer through autumn.  As I have mentioned before in this blog, Viburnums are self-sterile, so you need to have more than one genetic individual of each species to get berries.  Fortunately a local nursery is offering seed grown, wild-type plants so I won't have to worry about self incompatibility.  Wild-type Viburnums can get too large for many landscaping situations.  There are a number of more compact cultivars for garden use, such as the 'Blue Muffin' (aka 'Christom') shown here.  Together the Viburnums and the Hawthorn or Chokecherry will provide a nice edge habitat for with both food and shelter for wildlife.

Finding a Mate for My Plants

Berries of Winterberry Holly persist into well into winter
 when they provide late season food for birds.

Shortly after we moved into to our new place I identified a nice looking Winterberry Holly (Ilex verticillata) growing near the front door.  It was mid fall and I didn't see any berries on the shrub.  This meant that either it was a male plant or that there were no compatible males within 100 feet to provide pollen.  The bright red berries of Winterberry are its main ornamental and ecological feature. 

Female flowers have a large central ovary surrounded by undeveloped
stamen-like structures (lacking anthers).  This plant was blooming in early June.

I had to wait until the following June to get a good look at the flowers.  After careful examination it turned out that this plant was in fact a female.  The solution was to find a suitable mate, that is one with a similar bloom time.  I found a male cultivar at a nearby nursery called ‘Jim Dandy’.  I sat him next to the established female for a few days while I located a nearby spot to plant him.  

Male flowers have well developed stamen and a very small ovary-like center.
The male plant seemed to attract smaller sized insects.

By September I noticed a few of red berries on the plant.  Success!  I hope to see more berries next year as there will be a much longer time for pollination to occur. 

These red berries were formed by mid-August.  

One of my goals in designing a landscape is its habitat value.  That is, what does the landscape gives back to wildlife in the form of food and shelter.  So when I select plants I look for ones that produce flowers, fruits and/or seeds that wildlife can use.  When selecting plants from a commercial nursery many of them are cultivars, which are genetically identical.  This becomes an issue in the habitat garden if the plants are single sexed (dioecious).  It is also a problem for plants that have both male and female flowers on the same plant (monoecious) or have perfect flowers (both male and female parts in the same flower) if the plants are not self fertile. 

All this plant fertility can have a down side.  In a formal garden production of viable fruits and seeds may lead to increased weeding and spreading of plants out of their designed boundaries.  Also, some consider that the mess that falling fruits create outweighs providing food for birds and other wildlife.  Personally I think of the landscape as a dynamic thing that changes over time.  In the designed landscape plants need to be kept under some degree of control, but I really enjoy seeing native species spreading to new areas where they are happier than in my initial design.

Here are the flowers of a female persimmon.  They have large ovary structures.
Male flowers are narrow at the base.

My experience with the Winterberry Holly has heightened my awareness of dioecious plants.  I want to generate as much natural food for wildlife as possible.  Also I would like to grow some ‘wild’ fruits and berries.  Persimmons (Diospyros virginiana) are dioecious.  My established persimmon is a female, but I have not seen any fruit on it.  I have brought in four more new wild-type plants, at least one of these should be male.  I don’t know of any named male cultivars of persimmon; however there is one called ‘Meader’ that is self-fertile. 

In general female plants need at least one pollen source (male) close enough that pollen can be transferred.  This transfer can be by wind (grasses and many trees) or by insects (vectors) most flowering plants.  For native hollies, like Winterberry, a male should be located with in 50 ft for effective pollination, though pollination over greater distances (100-200 ft) may be possible. 

Female Box Elders are covered with seed pods (samara) in the fall.
I noticed some squirrels eating them right off the tree.

Some other dioecious plants that I have are Box Elders (Acer negundo), Junipers, Tupelos (Nyssa sylvatica), Yews and Goatsbeard (Aruncus diocus). 

Some plants with perfect flowers are not self-fertile.  This may not be convenient for a habitat gardener with limited space for lots of plants. However, it works out on the larger scale to provide the greater genetic diversity adaptation to change and continuation of the species.  I have posted a number of times about the difficulty of getting Viburnums to bear fruit when only a single cultivar was planted.

There are some practical situations where limiting plant fertility and reproduction is called for.  In urban landscapes Ginkgos are very successful street trees.  The fruits, however, are loaded with butyric acid and smell of dog poo when stepped on.  For this reason most cultivars in the trade are males.  In my last post about Jerusalem Artichokes I noted that these are not self-fertile.  By only using only a single cultivar one limits the risk that this somewhat aggressive native will spread by seed. 

Another issue for some in urban and suburban landscapes is pollen allergies.  In many cases these are due to the (over) use of male cultivars.  Males don’t produce messy fruits, but they still send out their pollen.  This results in a type of air pollution that effects sensitive individuals.  While searching for information about dioecious plants I came across an excellent resource book by Thomas Ogren titled Allergy-Free Gardening.  This book contains a lengthy list of dioecous plants and the sex of individual cultivars.  There is also an allergy rating for a wide variety plants including monoecious plants and those with perfect flowers.  I did not realize that many maples, such as Red and Silver Maples, came as separate male and female plants.  Since I am more interested in facilitating plant fertility for enhancing habitat value I see using this book differently than the author intended.  But, if I had a client with particular allergy problems this book would be an excellent resource for plant selection to design a low-allergen garden.

Creating Native Plant Communities

Many contemporary gardens are artful compositions designed to show off beautiful plants and elicit an emotional response. A main goal is that these compositions be ‘readable.’ This often requires that the ground plane be a smooth, weed-free layer of mulch. The ecological function of the plants and their interrelationships are not of primary concern. A more naturalistic approach to landscape or garden design puts a greater emphasis on the ecological function of the garden; this includes a well functioning plant community.

In a plant community there are plants to fill all available spaces, to the extent that the soil and moisture conditions allow. The spaces are filled on both a spatial and a temporal basis. There are different plants growing and receding over the course of a year. For example, one spot may be occupied by a wild geranium in the spring, followed by a big-leaf aster later in the summer and into fall, and all this could be happening beneath a shrub or small tree. The benefits of the diverse community of plants is that the ground is always covered, which blocks out weeds without the addition of a layer of mulch. These plant layers also provide cover for many beneficial insects – reducing the need for pesticides.

Another huge advantage of working with plant communities is that all these plants grow under very similar conditions. So soil conditions, water needs, climate and light requirements are all consistent and you don’t need to fuss over any individuals in the garden.

Designing a Plant Community

In nature, plant communities eventually develop on their own. In the residential garden we can play a role in what that community looks like. The first step is to determine the type of habitat you will be working with. Edith Roberts and Elsa Rehmann in American Plants for American Gardens, first published in 1929, taught about designs that were sensitive to the site and how to use appropriate natural plant communities in those landscapes. They describe habitats and provide lists of plants appropriate to rural Connecticut.

Another book with more emphasis on the design process is Natural Landscaping – Designing with Plant Communities, by John Diekelmann and Robert Schuster. These authors draw their examples from native plant communities found in the northeastern quadrant of the US. They describe the main plant regions and how the plant communities function in them. In the back of the book are lists of native plants found in 13 types of communities ranging from boreal forests in the north to savannahs and dry prairies.

For even more detailed descriptions of natural habitats I would look to resources like Wetland, Woodland, Wildland. A Guide to the Natural Communities of Vermont, by Elizabeth Thompson and Eric Sorenson. This book describes the features and major plant species encountered in over 80 natural communities found in Vermont. Similar information can be found for states or regions in books or on websites. Some of those are listed at the end.

Plant Native, an organization based in Portland, OR, is dedicated to using native plants in a more natural way. They offer some excellent guidance on their website along with region-specific plant lists. One particularly useful bit, taken directly from their site, is to realize that …

“…in some instances, human development alters the characteristics of a site such that it may be advisable to use plants from a neighboring region. For example, plantings in urban and suburban areas may receive reflected heat from streets, sidewalks and/or walls or be in media that receives less moisture than normal (e.g., next to a paved area – the pavement blocks rain from entering soil). Accordingly, using plants from a neighboring region that support higher temperatures and/or drier conditions may be more appropriate” (See http://www.plantnative.org/rpl-nes.htm)


Once you have a handle on the area you are working with you need to select the plants to fill the appropriate layers: ground covers, herbaceous perennials and grasses, woody shrubs, small and/or large trees. A typical foundation planting might be modeled on a forest edge or savannah community. Larger or more rural properties may have opportunities to use forest or prairie communities.

An example of a front yard planting modeled on a savannah would consist of some scattered trees like oak or pine under-planted with some shade tolerant perennials and shrubs. Open area would be planted with species preferring full sun. It is important that all the ground spaces be filled to block out weedy intruders.
While you can put together a plant community based on books and websites, there is nothing better than visiting natural sites and seeing some different plant communities. Visiting nearby sites also gives an idea of the native plants that work in your area. Many of the books and websites sited reference examples of places to go to experience these communities first hand (Diekelmann and Schuster’s book lists sites throughout the Northeast US).  Many botanic gardens have examples of native plant communities - and these have labels!  Garden in the Woods, in Framingham, MA and The Lady Bird Johnson Wildflower Center, in Austin, TX, are two of my favorites.


Additional Resources:
Books-
Plant Communities of New Jersey, by Beryl Collins and Karl Anderson

Web:
Natural Communities of Rhode Island

Classification of Massachusetts Natural Communities

Plant Native Website

Larry Weaner Landscape Associates  Larry Weaner has given some some great talks about work using plant communities.  Check out the website to see where he will be making future presentations.

Selection of Regionally Native Plant Species

If you want to get really thorough about creating habitats for native wildlife, the plants you choose should be native to your area. In addition they need to be appropriate to the habitat you are working with, such as uplands, woodlands, wetlands, etc. There are two major challenges here. The first is to learn the plants that are native to your area, and the second is to find a source for the actual plant materials. Collecting plants from the wild is not an accepted (or legal) practice in all but a few rare cases. (Check this link to NEWFS for more details on plant collection.)

A few years ago I was fortunate to be given a copy of The Vascular Flora of Massachusetts, A County Checklist by Bruce Sorrie and Paul Somers . This provides a listing of wild-growing plants in Massachusetts, their status as native or introduced, and in which counties they are found. It is a rather technical source, but is a great help in developing a native plant palette. Other states have similar listings of native flora. The Flora of North America (FNA), available on-line, includes regional occurrence and habitat information along with the species descriptions. This is a work in progress; information on just over half of the plant families has been published so far. Gleason and Cronquist, The Manual of Vascular Plants of Northeastern United States and Adjacent Canada gives this type of information in book form. One book I have found very useful for learning about plants for a given habitat for New England is Wetland, Woodland, Wildland. A Guide to the Natural Communities of Vermont by Elizabeth Thompson and Eric Sorenson. The USDA-GRIN taxonomic database lists native ranges to the state level for many native plants. You can also do searches on the USDA Plants database by state(s) to find lists of plants growing ‘wild’ (use the advanced search options). A website with a good lists of native plants for use in residential landscapes, including northern New England comes from ‘Plant Native’. There is also a reference section there listing resources appropriate to other parts of North America.


Armed with this information you can check out what native plant suppliers have available. Finding suppliers close to home can be of benefit if the plant materials they are propagating from are drawn from local sources, or at least from similar climates. A similar situation exists for seed. It would not hurt to ask your seed suppliers where their seed comes from. It is my understanding that much of the commercially available seed for native plants comes from Ernst Conservation Seeds, based in Pennsylvania. There are also many regional seed companies operating in the Midwestern and Southwestern US supplying regionally native seeds. I have found that the options for regionally native seed suppliers in the Northeast is more limited. If anyone has any recommendations for suppiers in the Northeastern US, I would appreciate hearing from you!


The real strength of using native plants comes when you use them in complete communities. I will explore some resources and concepts for assembling a native plant community in an upcoming blog.

So you like birds and butterflies? Better make room for Caterpillars!

When I started my project on the use of North American native annuals and biennials in Residential landscapes, I began to list some reasons for using native plants. This list included the particular benefits of annuals and other short-lived species that come with the greater emphasis on reproduction, resulting in more pollen, nectar and seeds. To be successful these are dependent on the pollinators gardens, the butterflies and bees that so many gardens wish to attract to their.

After a little more thinking and reading books like ‘Bringing Nature Home’ by Douglas Tallamy and Sara Stein’s ‘Noah’s Garden’, I began to appreciate that if you want butterflies, there must be a place for caterpillars nearby. Caterpillars are not only the source of butterflies; they are also an important source of food for birds. Insects, particularly herbivores, are a major component in the diet of nestlings.

Douglas Tallamy points out that most species of caterpillars are specialists, in that each has evolved to eat only a narrow range of plants – ones that they have co-evolved with for many thousands of years. Exotic and non-native plants ( ones that have not shared an evolutionary history) are of little use to these specialists. The bottom line is that most native insects need their own native food plants to survive.

Another aspect to nurturing pollinators is for the gardener to develop a tolerance for leaves with a few holes in them, and not to run for the pesticide at the first sign of attack by these native herbivores. In an ecologically balanced environment there are sufficient predators that will keep the caterpillars and other herbivores in check. Take a look at some websites or blogs on organic and habitat gardening approaches, such as the National Wildlife Federation (www.nwf.org/In-Your-Backyard.aspx) or http://www.ecosystemgardening.com/ , to learn more about creating a fully functional habitat garden.

Here's an example of a caterpillar infected with  parasitic wasps.

To learn which native plants support a given species of caterpillar/butterfly, check out the appendices in ‘Bringing Nature Home.’ Also the website for Butterflies and Moths of North America (www.butterfliesandmoths.org/ ) lists many facts about butterflies and moths found in North America, including their host plants for their larvae. (This site is searchable by insect’s species and state; doing the reverse, to find a list of insects feeding on a particular plant is not trivial.) The Wildflower Center’s website lists some plant-insect relationships in with their plant descriptions.

I’ve heard a little bit about putting sacrificial plants in the back of the garden to draw herbivores out of the more ornamental parts of the garden. Has anyone out there had experience with this approach?

As more native habitat is converted to human use, incorporating native plant species into the residential landscape is a step in the right direction toward supporting out native wildlife.