Gardening in Virginia: zones, frost dates and when to plant

Mountains, Piedmont and Coastal Plain

Virginia’s climate changes from west to east. NOAA’s state climate summary describes a humid state with very warm summers and moderately cold winters, where the Appalachian and Blue Ridge Mountains in the west and north run cooler and drier than the tidewater coast. Parts of the central mountains get less than 40 inches of precipitation a year, compared with about 50 inches along the coast. In summer, a high-pressure system off the Atlantic pulls moist air inland, which brings warm, sticky weather and frequent afternoon thunderstorms.

Virginia Tech’s soils chapter of the Agronomy Handbook divides the state along similar lines:

• Appalachian Plateau and Ridge and Valley (far west): steep, often shallow and stony soils on the slopes. The limestone valleys hold the most fertile ground, but some of their clay subsoils shrink and swell as they wet and dry.
• Blue Ridge: a narrow band of mountains where steep slopes, stones and shallow soil over bedrock are the main problems.
• Piedmont: the largest region, running from the Blue Ridge east to the fall line through Arlington, Fredericksburg, Richmond and Emporia. Soils are highly weathered, acidic and low in natural fertility, often with red clay subsoils. The handbook notes that soils east of a line from Martinsville through Appomattox to Fredericksburg run warmer.
• Coastal Plain: deep, sandy-surfaced soils east of the fall line. Many are naturally infertile, and the sandier ones dry out in summer droughts. Closer to the coast, the water table sits nearer the surface.

Why planting times vary so much

Virginia Cooperative Extension’s Virginia’s Home Garden Vegetable Planting Guide (publication 426-331) points out that the state’s mountain terrain packs very different conditions into short distances. Its example is Roanoke County, which spans four hardiness zones with a 30-day difference in planting time among them. Slope matters too: south-facing slopes are warmer and north-facing slopes cooler. The guide’s advice is to adjust its dates to your own site and experience. Use the frost dates for your city above as a starting point, then shift for elevation and exposure.

Planning the Vegetable Garden (426-312) adds that low spots, the base of a hill and the foot of a slope closed off by a solid fence all collect cold air. Those spots warm slowly in spring and get frost first. It suggests contour rows, terraces or raised beds on hillsides to control erosion, and a windbreak if the site is exposed.

What Extension recommends

The planting guide is built around two seasons, not one. For each crop it lists a spring window and, where it fits, a fall window:

• Fall-only crops: Brussels sprouts and rutabaga are listed for fall planting only, and garlic goes in during fall.
• Spring-only crops: garden peas, bulbing onions from sets, potatoes and the warm-season crops such as sweet corn, okra, sweet potatoes, melons and winter squash are spring or early summer plantings only.
• Both seasons: broccoli, cabbage, carrots, beets, kale, collards, lettuce, spinach and turnips can be planted in spring and again from midsummer into early fall for a fall crop.
• Season extension: row cover fabric and cold frames can stretch planting and harvest by two to four weeks at each end of the season.
• Succession planting: sow crops like snap beans, lettuce, radishes and spinach every two to three weeks within their window to keep the harvest coming.

The guide also gives spacing, seed per 10 feet of row and suggested plants per person, which helps when you’re working out garden size.

Planning the Vegetable Garden recommends planning the garden in summer, preparing soil in fall and ordering seed by January or February, since some crops can be started indoors as early as mid-February. Put tall and trellised crops on the north side so they don’t shade shorter ones. To limit insects and disease, avoid planting the same crop family in the same spot more than once in three years. In humid weather, give plants enough room for air to move between them.

Soil and water

Almost all Virginia soils have a pH below 6.2, according to the soils chapter, and acid soils need regular lime and fertilizer as a soil test directs. In the Piedmont, lime also keeps aluminum in the subsoil from becoming a problem. On sandy Coastal Plain soils, over-fertilizing is a concern because many gardens sit close to streams and other water.

Planning the Vegetable Garden puts vegetable water needs at about 1 inch a week, and up to 2 inches on sandy soil, counting rain. Water until the soil is moist 6 inches down. It also warns against gardening where buildings with lead paint once stood. If you’re unsure about a site, have the soil tested for lead.

Getting a soil test

The Virginia Tech Soil Testing Lab analyzes soil from the public and recommends lime and fertilizer rates. Reports are usually ready within three working days of receipt and are emailed directly to you, with a copy available to your local Extension office. The lab names your county or city Extension office as the first place to ask about sampling or reading results.