Week of May 13, 2002
Submitted by Calvin Finch, Ph.D., Manager, Conservation Division, Water Resources & Conservation Department, SAWS, and Horticulturist

MAY GARDENING CALENDAR

 

May is the prime lawn growing month. Temperatures are high enough to warm the soil, but mild enough that plant processes are not disrupted. Rain is usually sufficient in May to encourage good growth. Expect the St. Augustine and Bermuda grass to spread to fill any areas of grub, fungus, or freeze damage. Zoysia and buffalo do not fill damaged areas as well but they are actively growing. To speed the filling process, pieces of sod can be placed in large dead areas. Help the growth along by applying slow release lawn fertilizer to the lawn.

 

In the vegetable garden, keep the tomatoes well fed and well watered. If there is any break in the transpiration stream of water through the plant, blossom end rot will occur. Blossom end rot is recognized as a black, hard scarring on the bottom of the tomato. The symptom is directly caused by a temporary shortage of calcium during a high growth period, which occurs when the water flow through the plant carrying calcium is disrupted. It is almost impossible to prevent some blossom end rot as our high temperatures move from 85 to 95 degrees F., especially in container-grown tomatoes but frequent drip irrigation and mulch helps. Blossom end rot can be cut off the fruit if you want to use the tomatoes. In our soils calcium fertilizers such as epsom salts really do not help. Water and drying are the key. We have plenty of calcium in the soil.

 

There are several caterpillars attacking trees and shrubs now. Canker worms are the caterpillars hanging from the trees on web lines. Tent caterpillars are the furry worms covering the ground, patios, and plants in some locales. A Bt. Product such as Dipel, Thuricide, or Bio-worm Control will kill caterpillars if it is dusted or sprayed on foliage where they are feeding. In most cases, however, the caterpillar feeding is not a threat to the plant. The plant will replace leaves that are eaten.

 

In the best of times the health of red-tip photinias is threatened. The normal pattern for red-tip photinia in San Antonio is for them to do well for 5 years and then begin to show chlorosis (yellowing) due to iron deficiency. Shortly after the chlorosis appears the leaf spot attacks and the plants become weaker and weaker until they die. You can slow the process by mulching and adding iron sulfate or an iron chelate product to the mulch, but most photinias are short lived. This year the fungal leaf spot is really widespread. Even young healthy plants have the disease. There is no treatment that works. Young plants may recover but the cure is usually temporary. Select hollies, nandinas, or xylosma for a longer-lived large shrub.

 

The reseeding annuals and perennials such as bluebonnets, poppies, coreopsis, larkspur, and columbine need to be left in tact until the seeds mature if you want them to reseed. Remember the seeds must reach bare ground if the reseeding is to be successful. The process does not work if the soil is mulched or the plants are growing in sod.

 

Naturalized bulbs such as paperwhites and daffodils must also be allowed to brown before the tops are cut back. The leaves are producing the nutrients needed for the bulbs to accomplish next year’s growth as long as they are green.

 

Plant the hot weather blooming plants in May. Lantana, zinnias, caladiums, vinca, esperanza, firebush, moss rose, purslane, poinciana, and Mexican bush sage are all good choices. On some sites snapdragons are becoming overrun by rust. Recognize it by the rusty colored spores on the underside of the leaves and the light shadows on the top of the leaf. The blooming declines quickly when rust appears. Relegate the rust-infected snaps to the compost pile. It is also time to discard the pansies and other cool weather bloomers. Prune back your dianthus with the string mower and you may enjoy another month of bloom.