During March, the calendar—and sometimes the weather—turn to spring. By the end of the month, as temperatures rise and soils dry, we may see suitable gardening conditions. Native plant garden tasks this month include pruning, trimming back perennials, planning for spring prescribed fire in several garden areas, ordering plants, and contacting garden volunteers.
This month, Friends of the Arboretum offers the annual native plant sale advance order (orders are due March 25, with plant pickup on May 11). You can select from a wide range of native trees, shrubs, vines, herbaceous forbs, grasses, and sedges. FOA provides plant information sheets with your purchase.
When selecting new trees and shrubs for your garden, plan ahead for the mature size of the plant. Shading within a few years will change light levels dramatically for the ground layer, so consider savanna or woodland plants for an area where small trees are in the canopy. Most shrubs will thrive with full sun or very light shade, for example, in an edge. Of the woody plants offered in the FOA sale, some have showy flower clusters and fruits: black chokeberry (Aronia melanocarpa), grey dogwood (Cornus racemosa), American elderberry (Sambucus canadensis), and nannyberry (Viburnum lentago). Distinctive bark patterns are present in ironwood (Ostrya virginiana), ninebark (Physocarpus opulifolius), bur oak (Quercus macrocarpa), and red-osier dogwood (Cornus stolonifera) as they mature. Shorter woody species (under 3′ in height) such as New Jersey tea (Ceanothus americanus), dwarf bush honeysuckle (Diervilla lonicera), and Carolina rose (Rosa carolina) have excellent value to pollinators and other wildlife.
When planning a new herbaceous native plant garden bed or border, here are guidelines for the number of plants needed. If plants are spaced about 12″ apart, two plug trays (76 plants) will fill a triangular corner garden with sides 12′ long. Alternatively, two trays will fill a border 4′ x 30′ with the same plant spacing. To create a naturalistic design, lay down a garden hose to visualize and mark a curved edge for your planting bed or border. Then you can remove sod or use a different method to prepare the area for planting.
For example, to establish a relatively short stature pollinator garden in an area with medium soil moisture that is in full sun for most of the day, I recommend the “prairie garden” mix, along with half-flats of prairie blazing-star (Liatris pycnostachya) and Culver’s-root (Veronicastrum virginicum). Both of those have taller flowering spikes, but not dense tall foliage.
For a tall pollinator garden border that size (could screen a fence line), use 2 flats of the “pollinator garden” mix. Adding 2 more half-flats of any of the forbs in the mix or Culver’s-root, will cover an area 50 percent larger, if desired. These gardens can be installed in phases over a few years, making the work more manageable. When starting a garden with plugs instead of seeds, you will have flowers in the first season.
In an area with higher soil moisture and full sun, the rain garden mix will provide a tall garden that will also have value for pollinators and wildlife. The shape of a rain garden depends on site details, but you can calculate the number of plants needed by closely estimating the area in square feet, which also will be the number of plants needed for the recommended spacing.
Planning in the last few weeks before the growing season starts will improve your garden now and for years to come.
—Susan Carpenter, Arboretum native plant gardener