Longer and warmer days, higher sun angles, and mud mark the beginning of spring this month. By the end of March, several Native Plant Garden areas may be blackened and re-sprouting after prescribed fire conducted by the Arboretum’s professional crew. Outdoor garden tasks include trimming and clearing, checking for storm damage, and looking for signs of spring. Plant orders, presentations, writing, and planning are in progress indoors. We are looking forward to welcoming garden volunteers as weather permits.
Many prairie and wetland species are suitable for the range of soils and conditions in home gardens. Prairie plants will grow well in areas with six or more hours of full sun per day. Sites that slope toward the south, east, or west are well suited for a prairie garden. As always, for best results, match plant selections to your soil type(s). To help with garden planning for this upcoming season, here are recommendations for plants that will bloom in August-September in open, sunny spaces in your garden.
If you have a small area or want to preserve views across the garden, select shorter prairie grasses and forbs (flowering non-grasses). For dry sites, grasses include little bluestem (Schizachyrium scoparium), prairie dropseed (Sporobolus heterolepis), and side-oats grama (Bouteloua curtipendula). Forbs include silky aster (Symphyotrichum sericeum), wild petunia (Ruellia humilis), whorled milkweed (Asclepias verticillata), flowering spurge (Euphorbia corollata), dotted mint (Monarda punctata), gray goldenrod (Solidago nemoralis), rough blazing-star (Liatris aspera) and aromatic aster (Symphyotrichum oblongifolium).
On dry-mesic to mesic sites, tall grass species blooming at this time include big bluestem (Andropogon gerardii), Indian grass (Sorghastrum nutans), and switchgrass (Panicum virgatum). Tall forbs like prairie blazing-star (Liatris pycnostachya), smooth aster (Symphyotrichum laeve), sky blue aster (S. oolentangiense), showy goldenrod (Solidago speciosa), stiff goldenrod (Solidago rigida), and rattlesnake-master (Eryngium yuccifolium) will grow and bloom well. All of these species spread by seed, so harvesting seed when ripe will limit spread somewhat.
Wet-mesic and wetland species are best suited for areas with ample moisture, including low-lying areas or basins of rain gardens. Shorter species for these sites include bottle and cream gentians (Gentiana andrewsii and G. alba), great blue lobelia (Lobelia siphilitica), mountain mint (Pycnanthemum virginianum), Riddell’s goldenrod (Solidago riddellii), and cardinal flower (Lobelia cardinalis). Taller forbs include turtlehead (Chelone glabra), marsh milkweed (Asclepias incarnata), New England aster (Symphyotrichum novae-angliae), ironweed (Vernonia fasciculata), and Joe-Pye weed (Eutrochium maculatum). Most of these species disperse by seed rather than rhizome. Rain garden mixes are a good choice for home gardens where runoff can be captured and infiltrated on site.
One of our native shrubs, common witch-hazel (Hamamelis virginiana), blooms later in the season than any other species. Its unusual yellow flowers with strap-like petals bloom as the leaves attain fall color (also yellow) and drop. It grows well in moist, well-drained soil in full sun or in partial shade. This species is available at the Friends of the Arboretum online sale, along with many others that would be great additions to your late summer garden. FOA online plant orders close on March 15.
—Susan Carpenter, native plant garden curator