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Monthly Horticulture Tips

March Gardening Tips

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

Department of Horticulture & Landscape Architecture, Oklahoma State University

David Hillock, Consumer Horticulturist

Trees & Shrubs

  • Prune spring flowering plants, if needed, immediately following their bloom period.
  • Plant evergreen, balled and burlapped, and bare root trees and shrubs.
  • Anthracnose control on sycamore, maple, and oak should begin at bud swell. (EPP-7634).
  • Diplodia Pine Tip blight control on pines begins at bud swell.
  • Chemical and physical control of galls (swellings) on stems of trees should begin now. (EPP-7168 & EPP-7306)
  • Dormant oil can still be applied to control mites, galls, overwintering aphids, etc. (EPP-7306)
  • The first generation of Nantucket Pine Tip Moth appears at this time. Begin pesticide applications in late March. (EPP-7306)
  • Control Eastern tent caterpillars as soon as the critters appear.

Flowers & Vegtables

  • Cultivate annual flower and vegetable planting beds to destroy winter weeds.
  • Apply mulch to control weeds in beds. Landscape fabric barrier can reduce the amount of mulch but can dry out and prevent water penetration. Thus, organic litter makes the best mulch.
  • Prune roses just before growth starts and begin a regular disease spray program as the foliage appears on susceptible varieties. (HLA-6403 & EPP-7607)
  • Avoid excessive walking and working in the garden when foliage and soil are wet.
  • Start warm-season vegetable transplants indoors.
  • Divide and replant overcrowded, summer and fall blooming perennials. Mow or cut back old liriope and other ornamental grasses before new growth begins.
  • Your cool-season vegetables like broccoli, cabbage, carrot, lettuce, onion, peas, spinach, turnips etc. should be planted by the middle of March.
  • Watch for cutworms that girdle newly planted vegetables during the first few weeks of establishment. Cabbage looper and cabbageworm insects should be monitored and controlled in the garden EPP-7313).

Lawn & Turf

  • Remove excessive thatch from warm-season lawns. Dethatching, if necessary, should precede crabgrass control treatment. (HLA-6604)
  • Broadleaf weeds can easily be controlled in cool-season lawns at this time with post-emergent broadleaf herbicides. (HLA-6421)
  • Preemergent crabgrass control chemicals can still be applied to cool- and warm-season turfgrasses. Heed label cautions when using any weed killers near or in the root zone of desirable plantings. (HLA-6421)
  • March is the second-best time of the year to seed cool-season turfgrass; however, fall is the best time to plant. (HLA-6419)
  • Cool-season lawns such as bluegrass, fescue, and ryegrass may be fertilized now with the first application of the season. Usually, four applications of fertilizer are required per year, in March, May, October, and November. (HLA-6420)
  • Begin mowing cool-season grasses at 1½ to 3½ inches high. (HLA-6420)

Fruit 

  • Continue to plant strawberries and other small fruit crops this month.
  • Start your routine fruit tree spray schedule prior to bud break. (EPP-7319).
  • Remove winter mulch from strawberries in early March (HLA-6214).

Spring Cleaning

By David Hatlock, OSU, Senior Extension Specialist

Cleaning up the garden in late winter/early spring is a common practice. One reason for this is to remove debris that was infected with unwanted diseases and insects to reduce the chances of those organisms infecting new growth. Another reason is to allow the sun to reach the ground and warm it up encouraging new growth and provide space for the new growth. And another reason is some people just don’t like the look of all the old stems and foliage in the garden.

Recently, however, we have learned more about these dormant habitats and the importance they have on our native bees and beneficial insects. Many of our native bees are solitary bees and some nest in standing spent plant stems. Cavity nesting bees and some solitary wasps use hollow or pithy stems to construct their nests.

The folks at the Lurie Gardens in Chicago have been experimenting with and learning a lot about these habitats. The horticulturists at the Lurie Gardens say we still have a LOT to learn but have shared what they do know.

They have found that plants that have sturdy and fibrous stems with pithy, hollow centers that are about 1/8” to 5/16” in diameter are great for these stem nesting bees. The bees are usually nesting in the lower 24 inches of the stem. By leaving these stems somewhat intact throughout the year we are preserving their habitat and hopefully increasing a declining population of important pollinators. Leaving stubble that is 18-24 inches high in the garden may seem unsightly at first, but as the new growth develops in the spring, those stems will soon be hidden and may even provide additional support to the new growth.

Plants we know are host plants for native bees and solitary wasps include – Monarda fistulosa, Rudbeckia sp., Echinacea sp., Solidago sp., Aster sp., Asclepias incarnata, Vernonia sp., Veronicastrum virginicum, Agastache sp., and Hydrangea arborescens. Other species that the Lurie Gardens are experimenting with include Phlox paniculata, Kirengeshoma palmata, Thalictrum sp., Eutrochium maculatum, and Actaea sp.

 

Additional suggestions by the team at the Lurie Gardens to help preserve this valuable population of pollinators include – first, leave plant material standing through the winter. Second, identify plants that are desirable habitat and cut them high in early spring, leaving 18‑24 inches of stem stubble. Third, leave the stem stubble undisturbed for at least a year and a half. Fourth, repeat! Try to use the same individual plants each year – consistency is really helpful. Fifth, don’t just stick to the known host plants. Try a few others that might look like the right fit, because we still don’t know all of the potential habitat. And sixth, observe and share your findings!

Plants that don’t have these pithy, hollow stems can be cut back now. That might include many of your ornamental grasses and other perennials. New growth will begin to emerge soon on some grasses and perennials; waiting until new growth is several inches high will make it difficult to remove dead foliage without damaging the new growth; debris that has not been infected with pests can be left lying in the garden as a mulch or thrown into the compost pile to be used later as a soil amendment.