May in the Southeast marks the transition from spring productivity to heat-season management. In zone 8—9, daytime temperatures are regularly reaching 85—90°F by May, which ends production of cool-season crops and begins the heat stress window for tomatoes. In zone 7b, May is still productive spring weather with warm-season crops hitting their stride.
Per Clemson HGIC, average high temperatures in May: Atlanta 79°F, Columbia SC 83°F, Charlotte 74°F. These temperatures are at or approaching the threshold where tomato blossom drop begins (night temps above 75°F and day temps above 95°F).
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Tomato and vegetable management
Per NC State Extension, May tomato care in the Southeast:
- Fertilize monthly with a balanced fertilizer or tomato-specific formula; do not over-apply nitrogen at this stage — excess N delays fruit ripening
- Manage irrigation: 1—2 inches per week via drip or soaker hose; overhead irrigation promotes fungal disease; water in the morning
- Stake or trellis: if not done at planting, do it now; indeterminate tomatoes grow rapidly in May
- Monitor for early blight and leaf spot: lower leaves showing concentric brown spots indicate early blight; per Clemson HGIC, remove affected leaves and apply copper fungicide preventively
What to pull and replant: Per Clemson HGIC, as cool-season crops finish in May, replace with heat-tolerant summer crops:
- Remove finished broccoli, spinach, lettuce
- Plant southern peas, okra, sweet potatoes, and edamame — all of which need warm soil (65°F+)
- Okra: direct sow May 1—15 in zones 8—9; wait until May 15—30 in zone 7b
Fungal disease pressure
May's warm, humid conditions create high fungal disease pressure. Per Clemson HGIC:
- Black spot on roses: Apply fungicide every 7—14 days on susceptible varieties; potassium bicarbonate or myclobutanil are effective; Knock Out and Earth-Kind roses rarely need treatment
- Powdery mildew on cucurbits, phlox, bee balm: begins appearing in May in humid conditions; improve air circulation by thinning crowded growth; apply sulfur or potassium bicarbonate at first sign
- Botrytis on peonies: gray mold on stems and buds; cut affected stems at the base; improve air circulation; clean up all debris
Pest monitoring
Per NC State Extension, key May pests in the Southeast:
- Squash vine borer: adults begin flying in May in zones 7—8; lay orange-colored eggs on squash stems; per NC State, monitor stems for entry holes; apply row covers on squash plants to prevent egg-laying, remove for pollination
- Tomato hornworm: large green caterpillars appear in May—June; hand-pick or apply Bt (Bacillus thuringiensis (BT spray)) — effective when caterpillars are small
- Spider mites: begin appearing in hot, dry conditions in May; first sign is stippled, dusty foliage; per NC State, hard water spray to undersides of leaves is effective; apply insecticidal soap or neem for heavier infestations
Lawn care
Per Clemson HGIC, May is peak warm-season lawn management:
Bermudagrass:
- Mow at 1—1.5 inches for hybrid bermuda; 2 inches for common bermuda
- Fertilize with 1 lb actual nitrogen per 1,000 sq ft every 4—6 weeks through August
- May is the ideal time for overseeding thin bermuda areas before summer heat solidifies the turf
Zoysia:
- Mow at 1—2 inches; per Clemson, zoysia should be mowed more frequently than bermuda but at same height
- Fertilize May 1 with second application of season
St. Augustine:
- Monitor for chinch bugs: yellowing patches that don't respond to irrigation; look for small (1/5-inch) black and white insects at the thatch layer
- Apply insecticide labeled for chinch bugs if confirmed; per NC State Extension, chinch bugs are most active in hot, dry conditions
What's blooming in May (Southeast)
Per Clemson HGIC, spring-blooming plants at or nearing peak in May:
- Azaleas (Rhododendron spp.) and rhododendrons: finishing by mid-May in most zones; do not prune after May 15 — buds for next year begin forming in late May
- Iris: bearded iris (Iris germanica) peaks in zone 7b; Siberian iris (Iris sibirica) finishing in zone 7b; deadhead spent spikes but do not cut back the foliage until it yellows naturally
- Roses: first flush of the season; most rewarding bloom period in the South; hybrid teas and grandifloras are at their best in cooler May temperatures before summer heat degrades flower quality
- Clematis: Group 2 large-flowered types at peak in zone 7b—8; 'Nelly Moser' and 'The President' are classic Group 2 selections blooming on old wood in May
- Peonies (Paeonia lactiflora): late April through May in zones 7—8; support with peony rings installed before the buds open — one rainstorm on unsupported peonies flattens a full season's growth
Deadhead spent blooms on roses immediately: removes energy drain, encourages faster rebloom on Knock Out types.
Common mistakes
| Mistake | Consequence | Correct approach |
|---|---|---|
| Leaving cool-season crops in the ground past their season | Bolted, bitter plants; disease reservoir | Pull when bolting begins; replant immediately |
| Ignoring squash vine borer | Sudden plant collapse in June | Monitor from May 1; apply row covers |
| Overhead irrigation in the evening | Promotes black spot, powdery mildew, early blight | Water in morning; use drip or soaker hose |
| Pruning azaleas after May 15 | Removes buds for next year's bloom | Prune within 3 weeks after blooms fade only |
Frequently asked questions
When is the last planting date for tomatoes in zone 8—9? Per Clemson HGIC, in zone 8 (Columbia SC, Atlanta area), the last practical tomato transplant date for a productive summer crop is May 1—15. Transplants set out in late May will begin producing in July but will be in peak heat during most of their productive period. The spring window (March—June) consistently outperforms fall tomatoes in yield in most of zone 8.
Should I cut back roses after the first flush in May? Per NC State Extension, deadheading roses after the first flush promotes faster rebloom on reblooming types. Remove the spent flower cluster back to the first 5-leaflet leaf below the cluster. This is not aggressive pruning — just deadheading. The annual hard prune is done in late winter, not after spring bloom.
Recommended gear: Best Soaker Hose for Vegetable Gardens (2026) — our buying guide, with picks weighed against university Extension guidance and product labels.
Sources
- Clemson HGIC — May Garden Calendar
- NC State Extension — Vegetable Gardening
- NC State Extension — Lawn Care