Weather Averages
May 1: High 71, Low 50
May 31: High 78, Low 59
Precipitation: 5.6 inches

May Garden Calendar

Garden Help Desk

Master Gardeners will take your gardening questions at the Virginia Cooperative Extension Help Desk year-round. Call us at 703-324-8556 or email us at HelpDesk@FairfaxGardening.org.

Plant Clinics

We will return to select farmers markets in May. For a full schedule of plant clinics, go to the Plant Clinics page.

Trees & Shrubs

Prune all dead, damaged, or diseased branches any time of the year.
Shrubs
Prune flowering shrubs right after blooming. Best time to prune shrubs such as deciduous barberry, evergreen barberry, boxwood, camellia japonica, camellia sasanqua, cherry laurel, evergreen euonymus, forsythia, fothergilla, photinia, pieris, mugo pine, privet, deciduous viburnum, weigela, witch-hazel, yew.

Trees
Large deciduous or evergreen trees should be pruned by a certified arborist equipped to handle large limbs safely. Best time to prune deciduous trees such as crabapple, magnolia, maple, redbud. Best time to prune evergreen trees such as hemlock, pine, spruce.

    Diseases and Pests Commonly Appearing in May

  • Phomopsis Tip Blight on juniper, arborvitae, cedar and false cypress: New growth becomes pale, then red, then brown.
  • Exobasidium Galls on azalea: The gall coats the leaf or petal, causing it to curl and cup into a gall shape. It starts out green, then develops a fuzzy white coating. As the gall ages, it turns tan to dark brown.
  • Entomosporium Leaf Spot on red-tip photinia: The disease first appears as small, bright-red spots on both surfaces of new leaves. They grow into large purple to maroon spots and blotche, usually with red halos.
  • Cottony Camellia Scale on hollies: Look for cottony masses, usually on the underside of leaves.
  • Thrips on rose: Tiny insects feed on growing tips and flower buds, causing discolored and distorted leaves, flower petals that are discolored or scarred, and buds that fail to open. Feeding damage can cause browned areas or silvery-white patches.
  • White Peach Scale on cherry laurels: Infestations look like a pale, waxy crust on twigs or stems. The cast skins of males sometimes give the stem a fluffy appearance. Foliage of infected plants may look off color.
    For more information on pests and diseases of May, see the May Diagnostic Lab Preview.

Lawn

Home Turf, A Virginia Healthy Lawns Program
Provides advice specifically tailored to your lawn. Our Home Turf teams begin to provide services soon.

Mowing
Mow Kentucky bluegrass and perennial ryegrass to 1.5-2.5 inches,and tall fescue to 2-3 inches. Mow zoysiagrass and bermudagrass 0.5-1 inches. Use a mulching mower, and leave the clippings on the lawn to return nutrients to the soil.

Cool Season Grasses (fescues, bluegrass, ryegrass)
Fine to apply a nitrogen fertilizer at less than one pound per thousand square feet after May 15. Apply post-emergent herbicides when weeds are actively growing.
Warm Season Grasses (zoysiagrass, bermudagrass)
Cultivate and dethatch in preparation for planting. Apply post-emergent herbicides when weeds are actively growing.

Vegetable Garden

In Fairfax County, when to plant tender annual plants depends on location. To the east and south of I-395 from Alexandria to Springfield and I-95 from Springfield to the Occoquan River (Tidewater Zone), the last killing frost on average is April 10-21. To the north and west of these interstates (Piedmont Zone), the last killing frost on average is April 20-30. To be safe, add 10 days to these ranges: May 1 for the Tidewater zone and May 10 for the Piedmont zone.
Make sure plants are hardened off before planting. Do not be in a hurry to put tender annuals in the ground. Eggplant, tomato, and pepper transplants do not grow in cold, wet soil. Seeds of beans, cucumbers and squash may rot in the same cool, wet conditions.

Mulching
This is a great way to prevent weeds, maintain soil moisture and improve yields. Mulch your paths with straw or wood mulch. Beds can be mulched with newspaper (two sheets thick) and wood mulch over the top of the newspaper to keep it in place. Extension services have found that red plastic mulch (comes on rolls) improves the yield of tomato plants and eggplants. Silvery, plastic mulch improves the yields of pepper plants.

Cucumbers
Grow the plants up a trellis or netting to save space and keep the cucumbers away from crawling insects.

Winter squash and pumpkins
They will create large vines that cover the garden bed. When planting in hills, put a stake in the ground in the center of the hill to help you locate where to water the roots of the plants.

Flowering annuals
Plant a border of flowering annuals or perennials adjacent to your vegetable garden. They attract pollinators and add beauty.

Vegetable plants in pots
Almost any vegetable plant can be grown in a pot. You must use 5-gallon pots for tomatoes and eggplants. Peppers can be grown in 2-gallon pots. Tomato plants with determinate (smaller) vines are easier to grow in pots than plants with indeterminate vines. Fill the pots with soilless potting mix, not garden soil. Add a few tablespoons of limestone and a few tablespoons of garden fertilizer. Adding compost helps with soil structure and water retention. Keep the pots well-watered.

Flea Beetles
These tiny black beetles make many tiny holes as they feed on leaves. They particularly like eggplant, and they can be very destructive when the plants are newly set out. Keep them off the plants by covering with row cover. Pyrethrins, permethrin, and azadirachtin are insecticidal controls recommended by the Virginia Pest Management Guide.
Cultivate and dethatch in preparation for planting. Apply post-emergent herbicides when weeds are actively growing.

Flowering Annuals, Perennials

After last threat of frost has passed (see above), plant tender flowering annuals and perennials. Make sure the plants have been hardened off before planting. Let foliage from spring bulbs wither completely before removing it. Some annuals that do not require deadheading are begonia, impatiens, coleus, alyssum, ageratum, lobelia, vinca and salvia.

Disease first appears as small brown spots that expand and coalesce to form large brown areas. Spots take on an angular look as their spread is stopped or slowed at leaf veins. The disease begins on lower leaves.
For more information on May pests and diseases, see the May Diagnostic Lab Preview.

Houseplants

Move them outside when nighttime temperatures remain consistently above 50 degrees F. That will be mid to late May in Fairfax. Move them first to a relatively shady spot and gradually increase their sun exposure over the course of a week. Houseplants in clay pots can be planted directly in the ground while still in the pot, leaving an inch or two of the pot above the soil line. Make sure the pot has a drainage hole in the bottom. Houseplants in plastic pots should be transplanted to clay pots before placing in the ground.

References