The cooler temperatures, slowly cooling soils and increased abundance of moisture in fall make it an excellent planting season across Virginia. Generally speaking, as long as the soil is workable and remains above 40 degrees F, many dormant plants establish well when planted in autumn. Their roots grow and establish and by next spring are prepared to support the needs of newly emerging leaves and flowers. Virginia stretches across U.S. Department of Agriculture hardiness zones 5 through 7.
Horticulturists with Virginia Cooperative Extension say many trees, shrubs, perennials, and vegetables are successfully planted in the fall, from September to November. Slow-growing tree and shrub species, and those that are balled and burlapped (B&B) are best planted when they are dormant, likely in the month of November, according to West Virginia Cooperative Extension Service. Spring and summer-blooming perennials are best planted or transplanted/divided in September so their roots can establish in the cool, moist soil before hard freezes occur by early winter.
Proper soil preparation in late summer or early fall is needed to get any fall-planted tree, shrub or vegetable off to a good start. Deeply cultivating the soil to a depth of 12 inches and incorporating 3 to 5 inches of organic matter like compost or well-rotted manure improves soil quality. A fertile soil that is porous and moist is allowed to naturally settle and compact before sowing with seeds, transplant plugs or container-grown root balls. Do not fertilize plants in autumn, with the exception of annual flowers like pansies or leafy vegetables.
While cooler temperatures reduce water needs and uptake in the fall, plants can focus more energy in establishing root systems. Woody plants' loss of leaves permits all resources to be focused on growth of new roots into the garden soil before the soil freezes in December, or November in the higher mountain elevations in western counties of Virginia. Shorter days also tend to diminish the number of sprouting weeds, although a few cool-season weeds may germinate on bare soil patches, but not as much as in early spring.
Spring-flowering bulbs must be planted in autumn in Virginia; they need a prolonged exposure to cold to guarantee production of flowers next spring. Prime examples of bulbs planted in fall are daffodil, tulip, crocus, snowdrop, winter aconite, glory-of-the-snow and crown imperials. Summer-blooming lilies also grow from bulbs and are best planted in October according to Virginia Cooperative Extension. Cool-season vegetables, those that grow best when temperatures remain below 70 to 80, also are grown statewide from September to killing hard frosts after mid-November. Cool-season lawns are best seeded in early September for sprouting and initial establishment before winter.
If garden soil is free from frost in Virginia, the gardener must monitor moisture, especially for newly planted woody trees and shrubs. Daytime temperatures above freezing coupled with sunshine can dry the soil and root balls, leading to plant death. Continue to provide 1 to 2 inches of irrigation water to root balls across winter when soil is not frozen so plants will be alive and flush out new leaves in spring. Organic mulch helps moderate soil temperatures and conserve water.
Not all parts of Virginia experience the same weather. The higher elevations near Interstate 81 experience frosts and soil freezing much earlier than in the coastal areas around Norfolk. Timing of fall planting is adjusted accordingly, with projects completed earlier in autumn in the mountains as compared to the Piedmont and milder areas near Chesapeake Bay or the Atlantic.