When is the best time to plant perennials in Virginia?

Early spring and fall are the two best windows for planting perennials in Virginia. Virginia Tech's native plant guidance is to plant in late fall and early spring to reduce stress on the plants,^[1] and its shrub guidance makes the same call for woody plants: for container-grown shrubs the best time to plant is in the spring and fall.^[4] Midsummer is possible with pots, but it is the season when new plants struggle most.

Start with your frost dates

"Spring" in Virginia covers a lot of ground. Virginia Tech's planting guide covers hardiness zones 6a through 8b across the state,^[3] and Roanoke County alone has four different hardiness zones with a 30-day planting difference between them.^[3] Virginia Tech's planting guide lists average frost dates by zone:

• Last spring frost: in zone 6a the average last spring frost falls around May 5 to 15,^[3] in zone 7a around April 15 to 25,^[3] and in zone 8a around April 1 to 15.^[3]
• First fall frost: First fall frost runs from about October 5 to 15 in zone 6a to November 1 to 15 in zone 8a.^[3]

Look up your zone on the USDA Plant Hardiness Zone Map, then adjust for your yard: south slopes run warmer and north slopes cooler.^[3]

Spring planting

Plant hardy perennials once the soil can be worked and the hard freezes are behind you; tender plants and anything grown in a heated greenhouse should wait until after your last frost date. Spring planting gives a perennial a full season of growth before its first winter.

The catch is summer. Virginia Tech warns that plants put in during spring may not have established roots into the surrounding soil by summer.^[4] A plant that is not yet established relies on the limited water held in its own root ball,^[7] so a May-planted perennial can wilt in the first hot spell of June even when the bed around it is moist. Spring planting works well as long as you plan to water through the first summer.

Fall planting

Fall is often the easier season. The air is cooler, so leaves lose less water, while the soil is still warm enough for roots to grow. Perennials can take a few months or a year to establish,^[2] and a fall start lets much of that happen before the next summer.

Timing matters at the far end. Roots need several weeks of workable soil before the ground gets cold, and a Virginia Tech horticulturist notes from experience that plants that are not established are less cold hardy than established ones,^[7] so a perennial set out in December has less margin in a hard winter than one planted in September or early October. For gardens with no hose nearby, Virginia Tech suggests planting in the dormant season, November through February, as long as the ground is not frozen,^[2] because there is little top growth to supply with water until spring rain arrives. That advice suits tough natives more than fussy hybrids.

The mum exception. Garden mums sold in bloom each September are the classic fall mistake. To get them through winter, Virginia Tech says to plant garden mums in the ground in late August or early September,^[5] ideally buying them in bud, and adds that the later the mums are planted, the lower the survival rate.^[5] For a mum you want to keep as a perennial, spring planting is better still.

Dividing and moving perennials

Moving or splitting an existing clump follows a slightly different calendar. Virginia Tech's native plant guidance says the best time to thin or divide plants is October through April, or when they are not in bloom.^[2] A common rule of thumb is to divide spring and summer bloomers in fall and fall bloomers in spring, so you never cut into a plant just as it is putting energy into flowers.

Whatever the season, water is what decides success

The planting date only sets up the plant; watering gets it through. The most critical period for watering is right after planting and for the three weeks after,^[2] and Virginia Tech's rule of thumb is to check the soil about an inch down and water when it is dry, watering every 2 to 3 days in very sandy soil with no rain, and about once a week otherwise.^[2] Virginia Tech also notes that plants need an average of 1 inch of water per week during the growing season,^[6] from rain or the hose. Our guide to how often to water new plants goes through it month by month, and if plants droop anyway, see why new plants wilt after planting.

Before you dig a new bed, request a utility locate. Virginia 811's advice to homeowners is plain: "From fences to gardens, for any digging project, contact Virginia 811 three days before"^[8] you start.

Stop and call a pro if

• The bed is large, sloped or full of rock or construction debris, and preparing the soil is more than a weekend with a fork.
• Water stands in the planting holes a day after rain, which points to a drainage problem to fix before planting.
• The bed needs grading, a retaining wall or new irrigation lines, which are separate jobs with their own contractors.
• Utility marks run through the area you want to plant, or you hit a line, pipe or wire while digging.
• Plants keep declining after a full season of good watering, and you want someone to look at the soil and site.

Browse more lawn and landscaping answers, see garden and bed planting services, or look up lawn and landscaping businesses around Blacksburg. To have a bed planted this fall, describe the job once and local businesses quote it.