May in the Garden

May is for maintenance! Remove weeds from your planting beds before they go to seed. Once a weed produces seeds, you have greatly increased your workload. A light fertilizer application on your planting beds should be in your plans this month. Fertilize crepe myrtles and other plants scheduled to bloom with high phosphorous containing fertilizer, such as a 10-30-10 (Nitrogen- Phosphorous- Potash). Nitrogen promotes green color; phosphorous is for blossoms and fruits; and potash encourages root growth.

Continue to water your landscape wisely. Recently planted items need to be watered more often – once or twice each week. Drip irrigation on your annuals, perennials, and vegetables is a great way to go. Spray irrigation can harm plant leaves and some of the water evaporates before it even hits the ground. Wilted and rolled leaves will show that a plant is ready for a drink. Check the soil with your finger to determine if it’s time to water.   Make sure your trees get at least one deep irrigation this month. You can place a slow running hose (water is about the width of your little finger) at the root zone. Let it run for one hour, moving it every 15 minutes.

With the beginning of our summer heat, conserving water is an important goal.  All your beds should be covered with 2-6 inches of organic mulch. A layer of hay, dried leaves, or wood chips will reduce the evaporation of your soil moisture. Keeping weed seed from sprouting is a bonus to mulched beds. Keep mulch two to six inches from tree trunks.

Cool season annuals, like impatience and petunias, will begin to wilt each afternoon. They can be replaced with marigolds, pentas, salvia, and other heat loving annuals.

Insect damage and diseases could increase this month. Doug Welsh, professor and extension horticulturist at Texas A & M, shares his top five insect pests and plant diseases to watch for in the garden.


  1. Aphid
  2. Spider Mite
  3. Tomato hornworm
  4. Thrips
  5. Grasshopper


  1. Leaf spot
  2. Fungal mildew
  3. Fungal blight
  4. Fungal rot
  5. Viral mosaic

Your roses may begin to suffer from black spot, rust, powdery mildew, thrips, and aphids. Go to for treatment options. EarthKind and old-fashioned roses are more resistant to these diseases and insects. You can see how some are doing in the Rio Grande Valley at the Cameron County Master Gardener Arboretum’s Earthkind rose trial.  The Arboretum is located at the corner of Expressway 77 and Williams Road in San Benito.

To encourage compact bushes with many blooms, pinch your poinsettias and chrysanthemums every four leaves.


Flowers:  vinca, night and day purslane, moss rose, dianthus, caladium, coleus,                  celosia, marigold, zinnia

Vegetables:  okra, corn.

Herbs: cilantro, dill, thyme, malabar spinach, basil, rue, lemon grass.

Trees:  Live oak,  anacua, Rio Grande ash, chapote, brasil, Texas ebony, cedar elm, wild olive or anacahuita, royal poinciana (flamboyan), jacaranda, golden rain. Note: During warm months, it is safest to plant only container grown plants. If buying trees with rootballs wrapped in burlap, make sure the tree is green and healthy and the root ball is solid.

Palms: Texas sabal palm, Chinese fan palm, Mediterranean fan palm, Washingtonia fan palms, Pindo palms, Queen palms (or Cocus plumosa), and Phoenix roebellini.

Shrubs:  yucca, manzanita (barbados cherry), coral bean, Texas kidneywood, Salvia, lantana, butterfly bush (Buddleia), butterfly weed, wild petunia (ruellia), hibiscus.  Note: most of these shrubs attract butterflies and hummingbirds to your garden.

HARVEST: Green beans, cucumbers, cantaulope, tomatoes, onions, peppers, eggplant, peaches, blackberries, and citrus.

Information source:

  • Successful Gardening in the Magic Valley of Texas, Dist. VI, Texas Garden Clubs, Inc.
  • Native Trees- and Native Shrubs-of the Lower Rio Grande Valley, Texas Landscape Uses and Identification, Native Plant Project, P.O. Box 1433, Edinburg, TX
  • Texas Garden Almanac, Doug Welsh
  • Mary Beth Simmons on the Master Gardener Website