May Gardening Checklist: Clemson Extension Shares What Upstate Homeowners Need to Know
May 5, 2026
Clemson Extension Offers May Yard and Garden Tips for Upstate Homeowners
The Clemson University Cooperative Extension Service is reminding homeowners and gardeners to stay ahead of seasonal pests, diseases, and planting windows with key tips for May.
Pests and Problems to Watch
Japanese beetles can defoliate plants quickly. Carbaryl (Sevin) is an effective treatment; spray after 5 p.m. to protect honeybees and use liquid formulations rather than dusts. Fruit tree owners should inspect for fireblight, particularly if it was a problem last year, and spray blooms as a preventive measure.
Warm-season lawn owners should monitor for brown patch, dollar spot, and chinch bugs. Bagworms are another concern for trees and shrubs, favoring juniper, arborvitae, and pine but attacking many broadleaf varieties as well. Light infestations can be hand-picked; Bacillus thuringiensis is also effective. Oakworms and cankerworms may defoliate oaks this month, though trees typically recover on their own.
Vegetable gardeners should watch for corn earworm, cucumber beetle, and squash vine borer. Check tomatoes for blossom end rot as fruit forms; adding gypsum to the soil at planting or using a foliar spray can help prevent it. Affected fruit should be removed and discarded.
What to Do This Month
Plant summer- and fall-flowering bulbs such as dahlias, gladioli, cannas, and lilies once soil temperatures reach 55 degrees. Continue fungicide applications on fruit trees every seven to 10 days, holding insecticides until less than 10 percent of blooms remain to protect pollinators.
Apply a complete fertilizer to warm-season lawns this month. Fire ant bait should go down during the last week of April or first few weeks of May when ground temperatures are between 70 and 95 degrees. Aeration is beneficial any time a warm-season lawn is actively growing.
Homeowners planning a new warm-season lawn, including centipede, zoysia, Bermuda, or St. Augustine, should plant in spring or summer. Nutsedge control requires identifying the variety, either purple or yellow, before selecting a herbicide, and should be applied when the plant is actively growing.
Extension recommends one inch of water per week for most lawns and vegetables, accounting for rainfall, and cautions against daily watering. May through July is also a good window to stock bass in a recreational fishing pond.
Current vegetable planting windows include cucumbers, cantaloupes, and squash through May 15; okra, lima beans, and peppers through May 15 to 30; melons and southern peas through June 30; sweet potatoes through June 10; and tomatoes through May 30.
Additional resources are available at clemson.edu/hgic.
