May Gardening Guidelines

by Keith C. Hansen, Extension Horticulturist, Smith Co. – Tyler, Texas

April showers bring May flowers and lots of gardening activities. Visits to local nurseries and public gardens will stimulate lots of new ideas and possibilities. Here are a few items that can help you with your gardening activities.


Be sure to visit the Tyler Rose Garden this month where roses are the star, but not the only thing to see. Daylilies will soon be coming into bloom, and the Heritage Rose Garden displays old garden roses and a variety of perennials – definitely worth the visit!

While at the Tyler Rose Garden, be sure to check out the I.D.E.A. Demonstration Garden – where you’re sure to find an idea or two to take home and use in your own yard and landscape.


Although pansies are still looking great, it’s about time to pull them and plant summer flowering plants. There are too many to list here, but your choices are many, and nurseries are stocked with them. It’s better to go ahead and dig out the pansies even though they may still be looking quite good. Once it gets hot, they’ll go down fast. Annuals give you lots of color bang for your buck.

Transplant or sow seeds of angelonia, ageratum, sunflower, zinnia, morning glory, portulaca, marigold, cosmos (Cosmos bipinnatus with pastel colors and C. sulphureus with hot reds and yellows), periwinkles, gomphrena and gourds. Plant vinca (periwinkle), which prefers hot, sunny sites, later in May once the weather turns warmer.

For shady spots, grow these favorite plants: impatiens, coleus, caladium and begonias. Flowering tobacco (Nicotiana) is a great fragrant annual for partial shade.

Perennials for the sun include Shasta daisy, dusty miller, garden mums, coreopsis, mallow, salvia (many kinds), daylily and summer phlox. Shade loving perennials include hosta, columbine, phlox, ferns, violets, ajuga, and liriope. Achimenes, cannas, dahlias, caladiums and other summer bulbs can also be planted in May.

Some plants can be grown as either annuals or perennials. Lantana loves the summer heat and sun, blooming from late spring through first frost. Most years it will come back from the roots. Lantana comes in bush and trailing forms, and in many colors.

Firebush or Hamelia is another favorite summer bloomer with bright orange/red flowers that is a magnet for hummingbirds. It is usually slow to emerge after winter, and many folks simply replant it every year.


If you cut off old blossoms on early spring flowering annuals like pansies, snapdragons, stock and calendulas, you can prolong the flowering season a few more weeks.

Allow foliage of daffodils and other spring flowering bulbs to mature and yellow before removing. Do not hide or cover the their leaves.

Pinch back growth of newly planted annual and perennial plants. This results in shorter, compact plants with more flowers.


There’s still plenty of time to set out container shrubs and trees. While they will need regular watering this summer, be certain you are not pouring too much water on your new plants. Folks with sandy soil may have the tendency to apply lots of water, keeping the soil where there are currently no roots saturated with water. Roots do not grow well in wet, soggy soil. Regularly check both the surrounding soil and the original soil root ball with your finger to determine the need for supplemental water during the year.

Fertilize roses every four to six weeks with small amounts of a balanced fertilizer. Control black spot on roses with triforine (Funginex) or other labeled product.


The first application of fertilizer for centipede lawns should be made soon, and if you have not yet fertilized St. Augustine or Bermuda grass, it is certainly not too late. The best way to determine what type and how much fertilizer is needed is to have a soil test done; otherwise use a 3-1-2 or 4-1-2 fertilizer ratio.


As soon as tomatoes and peppers first set fruit, lightly apply nitrogen fertilizer (called side dressing) about 12 to 14 inches from the base of the plants. This supplemental feeding keeps the plants vigorous and growing, allowing them to set and mature the maximum amount of fruit without stunting the growth of the plants.

Cool season vegetables, like lettuce and spinach, will begin bolting (flowering) and quickly go down in quality once it gets hot. Harvest them soon and replant empty spots with warm-season vegetables like okra, sweet potatoes, pumpkins or watermelons.


Don’t take the description “evergreen” plants too literally, expecting leaves to persist forever. Plants like magnolias, live oak, gardenia, hollies and some azaleas lose some of their old leaves in late spring and early summer. The flush of new growth on many evergreens will cause older leaves to yellow and drop, sometimes all at once. It’s nothing to be concerned about; just nature putting on a new spring coat of green and discarding the old.

Unfortunately, the month of May is not be complete without a few pests messing things up. Here are a few of which you should be aware. If you know what might be showing up, you can periodically check your yard and take action before things get out of hand and more difficult to control.

Check azaleas for lace bugs. These small, slow moving, black insects with clear, lacy wings feed on the underside of the leaves. Damaged leaves look stippled or bleached and have small, shiny black specks on the undersides.

Leaf spot on Red Tip Photinia is a disease which can defoliate, weaken and potentially kill limbs. Indian Hawthorns can also get this disease which is characterized by dark, purple-colored spots on the leaves. Prevention is the best remedy to control Entomosporium leaf spot. First, rake up and remove all old, fallen leaves from underneath Photinias. The disease will be more severe if the leaves are frequently wetted, either by rainfall or by an irrigation system. If your sprinklers are hitting the plant’s leaves, make adjustments to prevent this from occurring.

A preventative fungicide spray will help control Entomosporium leaf spot, particularly if the photinias were affected last year. Alternate triforine (Funginex) or bayleton with chlorothalonil (Daconil, Bravo, Multi-Purpose Fungicide) during the rainy season. This disease can be difficult to control and new growth must be protected.

Aphids, or plant lice, can be found on tender, new growth of all types of plants. Aphids are small, soft-bodied insects that suck plant sap, often occurring in very large numbers. There are several naturally occurring enemies of aphids which can efficiently reduce an a small infestation. Usually beneficial insects (lady beetles, lacewings, parasitic wasps) do a good job of keeping aphid populations under control.

Look closely to see if plants with aphids have any parasitized aphids. Parasitized aphids appear fat, motionless, and salmon-colored. Very tiny wasps lay eggs in the aphid bodies. The eggs hatch and develop into small larvae which eat the aphid’s insides! A close inspection of parasitized aphids might even reveal a tiny exit hole where the new adult wasp emerged to continue the cycle of destroying more aphids. Obviously, there is no need to spray there if you find insect predators or parasites working over an aphid infestation.

Cabbage worms and loopers will be on all cole crops including broccoli, cabbage, collards, kale and cauliflower. The biological insecticide Bacillus thuringiensis (Bt), sold under several brand names like Biological Worm Killer, Thuricide, Dipel, etc, is a specific and very safe product to use to control these and other moth and butterfly caterpillars on vegetables and other plants. Use Bt late in the day and thoroughly cover the leaves with the spray.

Not all “critters” are pests, nor are all spots diseases – be sure to get any unknown suspect or problem correctly identified before considering treating with a pesticide.

Information given above is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by Texas A&M AgriLife Extension Service is implied.

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