Many gardeners are looking to bring both beauty and support for wildlife into their garden designs. One important way to do that is through creating a well-layered landscape. Join Extension Master Gardener Elaine Mills to learn some techniques for introducing diverse layers of vegetation in a variety of garden contexts, from reestablishing forest edges and planting around trees to refreshing foundation plantings, creating perennial beds, and rethinking front yard designs. Elaine will share ideas and lessons learned from her own garden and those of several Master Gardener colleagues.
Speaker: Elaine Mills, Extension Master Gardener
Zoom session, March 25, 2022
Video of Presentation
Addendum: Additional Details and Answers to Chat Questions
Elaine Mills, presenter of “Creating a Well-layered Landscape”
Many of the plants described during this presentation are native to Arlington County and the City of Alexandria in Northern Virginia, and most of them are also indigenous to the Mid-Atlantic Region.
- Viewers from other areas of Virginia will want to look for regional native plant guides. Links to free PDF versions of these guides can be found on the website for the Virginia Native Plant Society at https://vnps.org/virginia-native-plant-guides/
- Viewers watching from other states may wish to consult county-level maps at https://plants.sc.egov.usda.gov/java/ to confirm the presence of the plants in their regions. State native plant societies and local Extension offices should also be able to provide information on locally native species.
Further Responses to Questions Posed During the Q&A Session
Regarding a question on grass (and other plants) for wet areas,
- The warm-season native grasses, such as Little Bluestem (Schizachyrium scoparium), Switchgrass (Panicum virgatum), and Indian Grass (Sorghastrum nutans) have very deep root systems, making them drought-tolerant. They will tend to flop when the soil is too rich and moist, so they would not be good choices for wet areas.
- Cool-season River Oats (Chasmanthium latifolium), a tall (2- to 5-foot) woodland grass can handle soil moisture from dry to wet. It has beautiful oat-like spikelets that change color through the seasons. Be aware that this grass can spread vigorously.
- Native sedges in the Carex genus are perhaps even better suited to wet conditions as their natural habitats include banks of streams, floodplains, and wet prairies. Examples are Frank’s Sedge (Carex frankii), Gray’s Sedge (Carex grayi), Tussock Sedge (Carex stricta), and Fox Sedge (Carex vulpinoidea).
- Rushes, such as Common Rush (Juncus effusus), thrive in wet areas and do well in standing water up to 4 inches.
- Another way to handle wet areas might be to consider installing a rain garden. Penn State Extension has compiled this list of plants for rain gardens sorted by the three zones. The webinar Rain Gardens for Homeowners presents many more details on building these landscape features.
- If there is enough space, adding native shrubs will create multi-season interest with spring blossoms, summer to fall fruit, and autumn foliage color. Species which thrive in wet spots and tolerate saturated soil and periodic inundation include Black Chokeberry (Aronia melanocarpa), Buttonbush (Cephalanthus occidentalis), Spicebush (Lindera benzoin), and Sweet Pepperbush (Clethra alnifolia).
In response to a question on whether it is possible to mix plants from different forest plant communities,
- In natural settings, certain groups of plants will consistently grow together in natural communities because they share a preference for a particular position in the landscape (microclimates based on slope topography), characteristics of the soil (type, pH, fertility), water supply (location within a watershed and amount of precipitation), and exposure to the sun.
- Plants characteristic of the Acidic Oak-Hickory Forest are found on slopes with dry and less fertile soil, while those typical of the Mesic Mixed Hardwood Forest are found on low-elevation habitats with a moderate amount of moisture. That means that while there may be some species in common, many species may not be suited to both communities. See the Plant Compendium on the Earth Sangha website for details on the components of each group along with their frequency.
- There are, as I mentioned, certain “generalist” native plants that do well across a range of conditions. Using some of them could provide a starting point for introducing more native plants and the foundation for later applying a more community-based approach to landscape choices. See Generalist Plant Lists on the Earth Sangha website.
In response to a question on allowing growth of Virginia Creeper in trees, Dr. Doug Tallamy, author of Bringing Nature Home (pp. 276-278) advises against this practice.
- While in principle, native vines can be “good neighbors” in ecosystems, providing insects and fruit, there can be serious problems with woody vines, regardless of their geographical origin.
- All native woody vines in the East grow faster than trees, so the trees end up being unable to photosynthesize as their canopy foliage is smothered. The trees can also be pulled down by the sheer weight of vines.
- A blog from New Mexico State University comments that in addition to competing for light, vines will compete for water, and there is the potential for vines to girdle themselves as they wrap around a tree.
Choices of plants to interplant with spring ephemerals for when they go dormant include:
- Other ground covers, such as Allegheny Spurge (Pachysandra procumbens).
- Ferns, such as Marginal Wood Fern (Dryopteris marginalis) and Christmas Fern (Polystichum acrostichoides).
Regarding a question about native fruit trees,
- There are no species of apples or peaches that are native to North America.
- You may want to consider the native Sweet Crabapple (Malus coronaria). It has high wildlife value, attracting a wide variety of pollinators and serving as the host plant to many butterflies and moths. Unfortunately, it is susceptible to numerous pests and diseases, like cedar-apple rust.
- Other native fruit trees include
- There are also several native shrubs with edible fruit:
- A recorded class by our Extension Agent Kirsten Conrad on “Fruit Trees and Berries for the Urban Landscape: Natives” provides helpful information on the selection and culture of native plants that offer food and also satisfy ornamental landscape use.
On the question of removing and replacing Liriope,
- Liriope is a non-native species that is considered invasive in Arlington and Alexandria, VA, and throughout the southeast.
- My recommendation for replacement is the native Plaintain-leaved Sedge (Carex plantaginea) which has wide evergreen leaves and a similar habit.
- I have found hand tools, such as the Hori Hori knife or pick/mattock, are strong enough to help cut through the thick “turf” of Liriope without damaging the surrounding tree roots.
There were many questions in the chat on when to undertake spring garden cleanup.
- It’s helpful to wait as long as you can so that hibernating insects can have a chance to emerge from leaf litter and stems of native plants. Ideally, you should wait until daytime temperatures are consistently above 50 degrees F for at least 7 to 10 days.
- If you feel the urge to clean sooner, you can cut back plant stems to 12 inches or so and loosely pile the remaining debris and wait to do any raking until it is warmer.
- See this excellent poster by Heather Holm, an expert on bees and wasps, which clearly illustrates How to Create Habitat for Stem-nesting Bees.
- The recorded class “Leave the Leaves and Other Beneficial Practices” by Master Gardener Nina DeRosa provides more guidance and explains the process of using leaves in composting.
Although I didn’t mention Amsonia by its scientific name during the presentation, I mentioned several ways it could be used.
- I use Amsonia tabernaemontana (Eastern Bluestar) as a medium-high layer in the bed surrounding a tree. Several plants placed two feet apart spread together almost like a small hedge.
- Arkansas Bluestar (Amsonia hubrichtii) is native to Arkansas and Oklahoma, although it grows well in Northern Virginia. It has feathery foliage rather than lance-shaped leaves. Both species have the same light blue flowers and bright yellow fall foliage color, and both could be used in the structural layer of a perennial bed.
Regarding Mexican Feather Grass,
- Mexican Feather Grass (Nassella tenuissima) does not appear to be considered invasive in Virginia (as it is in California), but it is an extremely vigorous grass and often self-sows abundantly, spreading out of its designated place in the garden.
- Mexican Feather Grass (30 inches tall in bloom) is favored for its delicate, feathery texture and tolerance to heat and drought.
- There are several native grasses to consider as substitutes:
For suggestions on plants for a hell strip (the hot, exposed area between a sidewalk and the curb), see the section of my recorded class “Selecting Native Plants for Your Home Garden” on Perennials for Dry Streetscapes (beginning at 1:11:26). Among the species that would work well there are:
- Common Yucca (Yucca filamentosa)
- Creeping Juniper (Juniperus horizontalis)
- Yellow Wild Indigo (Baptisia tinctoria)
- Pussytoes (Antennaria plantaginifolia)
- Moss Phlox (Phlox subulata)
On the question of using Crepe myrtle,
- While this non-native (Lagerstroemia indica) is not listed as invasive, I feel that it is greatly overused. Sometimes a tree like this in our gardens may not spread in the immediate area, so it does not appear to be a problem. However, birds can carry seeds afar and, in my neighborhood, I have seen the plant spreading from one garden to other yards where it was not intentionally planted.
- I would recommend substituting several small native trees that have equally lovely blooms and will support wildlife by providing nectar and pollen and fruit or serving as larval host plants:
On the question of adding a level of canopy trees to a garden with an existing shrub layer,
- It will probably be best to bring in smaller specimens of those species to interplant.
- Three sources of advice for handling the process safely would be:
Comments on Chat Box Topics Not Posed During the Q&A Session
There was a great deal of discussion about native Violets.
- While they can volunteer in multiple locations from lawn to mulched areas, I find them quite easy to dig out and move to where I would like them to grow as a weed-suppressing ground cover.
- If you wish to intermix Violets with other native ground covers, such as Wild Ginger, allow the other species to get well-established first.
- Violets are an early nectar source and the primary host plant for fritillaries. The flowers are also edible.
One participant mentioned using edible plants, such as spinach and lettuce in spring and fall borders as a surprise for neighbors to enjoy.
- See the recorded class by Master Gardener Alyssa Ford Morel on “Edible Landscaping” for tips on mixing ornamentals, herbs, greens, and vegetables.
Another participant mentioned having problems controlling Common Milkweed (Asclepias syriaca).
- This plant spreads by seeds, so its spread could be limited somewhat by removing immature seed pods.
- It also spreads aggressively by underground rhizomes, sometimes at great distances from the original plant.
- To support Monarch butterflies, another option would be to plant Swamp Milkweed (Asclepias incarnata) or Butterflyweed (Asclepias tuberosa), which are less prone to uncontrolled spreading. The taller species prefers moist to wet soil conditions, while the shorter one grows in dry to moist conditions.
On the topic of a ground cover for an outdoor rabbit,
- Rabbits do not generally eat native grasses and ferns, but no plants are truly rabbit-proof.
- Sedges and evergreen ferns to try:
Some questions were posed in the chat regarding my own garden maintenance.
- My garden surrounds my home on a flat double lot of about ¼ acre. The original owner of the home was a gardener, so my soil was in very good shape from when I moved in 1985. I have no lawn. The entire back 1/3 of the property is the forest edge I have created. There is an allée of trees on the south side of the yard and a large, deep perennial bed along the north side of the yard. There are deep foundation plantings on both sides of the house and garage with paved paths running between them. These are linked to steppingstone paths in the backyard. I have planted 22 trees (9 of native species), around 75 shrubs (63 native species), and hundreds of herbaceous plants (80 native species).
- I devised the design of the paths and determined the location of the large trees. Construction of the hardscape and this planting was the only work undertaken by landscapers. I installed the shrubs when small and have only had assistance when some of them later needed to be moved.
- When major work needs to be done on the trees, I work with a professional tree care company. On two occasions, I have had help from a Master Gardener who is also a certified arborist help with pruning of smaller trees and shrubs.
- I maintain the perennial beds by myself with assistance from a Master Gardener colleague for maybe 6 hours a year in the hot summer months. I probably spend more time maintaining the non-native plants than the native ones. The maintenance tasks include:
- Late March: Pruning native wild hydrangea
- April: Spring clean-up which includes moving blown leaves away from basal rosettes of perennials; cutting back stems for eventual use of stem-nesting bees; trimming tattered foliage of sedges, ferns, and Lenten roses; and removing a few winter weeds and other debris
- May: Folding back foliage of daffodils; cutting back stalks of iris at end of bloom; creating support for peonies; cutting back seed heads of spring-blooming perennials and pinching and cutting back tall perennials (Joe Pye, New York Ironweed, New England Aster, Goldenrods) to control size
- June: Further cutting back, as needed
- July & August: Watering, as needed, during extended periods of drought; neatening overgrown perennials
- September & October: Cutting back any foliage with powdery mildew (peonies, phlox); dividing and replanting irises; raking leaves from paths into beds and forest area, retaining some for use in making compost
- November-March: No maintenance, except brushing off snow and ice from trees and shrubs, as necessary