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Monthly Gardening Tips

May Tips

Oklahoma Cooperative Extension Service, Division of Agricultural Sciences and Natural Resources

Department of Horticulture & Landscape Architecture, Oklahoma State University

David Hillock, Consumer Horticulturist

Bagworm on juniper.

Turf Grass

  • Cool-season lawns can be fertilized again. If you did not fertilize cool-season grasses in March and April, do so now.
  • Warm-season lawns may be fertilized again in May. (HLA-6420)
  • The seeding of warm-season grasses such as bermudagrass, buffalograss, zoysiagrass and centipedegrass is best performed in mid-May through the end of June. The soil temperatures are warm enough for germination and adequate growing season is present to promote winter hardiness.
  • Dollar spot disease of lawns can first become visible in mid-May. Make certain fertilizer applications have been adequate before ever applying a fungicide. (EPP-7658)
  • Nutsedge plants become visible during this month. Post-emergent treatments are best applied for the first time this month. Make certain warm-season grasses have completed green-up.
  • The second application of pre-emergent annual grass herbicides can be applied in late-May or early June, depending upon timing of first application. Check label for details.
  • Vegetative establishment of warm-season grasses can continue. (HLA-6419)


  • Annual bedding plants can be set out for summer color.
  • Plant summer bulbs such as cannas, dahlias, elephant ear, caladiums, and gladiolus.
  • Shake a leaf over white paper to look for spider mites. If the tiny specks begin to crawl, mites are present.

Trees & Shrubs

  • Prune and feed azaleas immediately after blooming.
  • Insect Alert: (EPP-7306)
    • Bagworms on juniper and arborvitae. (Late May)
    • Elm leaf beetles and larvae on elms. (Late May)
    • Mimosa webworms on mimosa and honeylocust.
    • Lace bugs on sycamore, pyracantha, and azalea.
  • Soak new transplants and newly planted trees unless rainfall is abundant.
  • Pine needle disease treatments are needed in mid-May.

Water Gardens

  • Clean out the water garden and prepare for season. Divide and repot water garden plants.
  • Begin feeding fish when water temperatures are over 50°F.

Fruit & Vegetables

  • Plant watermelon, cantaloupe, cucumber, eggplant, okra, sweet potatoes, etc.
  • Fruit spray programs should be faithfully continued during the next several weeks.
  • Late May is the best time to control borers in the orchard. Check for label recommendations and controls.

How To Produce High Quality Tomatoes

By David Hatlock, OSU, Senior Extension Specialist

  1. Select or prepare soil high in organic matter and sufficiently loose to allow for extensive vigorous root growth.
  2. Apply needed fertilizers and mix into the soil prior to planting.
  3. Obtain husky plants of recommended nematode and wilt resistant varieties. Set them into the garden as early as weather and recommended planting dates permit.
  4. Water in newly set plants with a starter solution.
  5. Provide protection from cutworms and other possible pests of the transplanting season.
  6. Use mulching materials around plants within one month following planting.
  7. Apply supplemental water as needed, drip irrigation being preferred.
  8. Control insects and spider mites as well as leaf and fruit diseases if numbers are increasing week to week.
  9. Windbreaks may be especially desirable as hot, dry weather develops.
  10. Maintain the identity of different varieties to evaluate their qualities and thus determine the more appropriate kinds for future plantings.

For more information on growing tomatoes see OSU Extension Fact Sheet HLA-6012 Growing Tomatoes in the Home Garden.