Extreme heat and drought impact fall garden plans

With extreme heat and little rain still on the horizon for Oklahoma, gardeners may need to alter their fall garden plans.

“There‚s nothing better than fresh produce throughout most of the year, but the lack of rainfall coupled with excessive heat may put a damper on successful fall gardening,” said David Hillock, Oklahoma State University Extension consumer horticulturist. “Typically, some of the best quality garden vegetables in Oklahoma are produced and harvested during the fall season when the warm days are followed by cool, humid nights.”

In ideal conditions, Hillock said plant soil metabolism is low; therefore, more of the food manufactured by vegetable plants becomes high-quality produce. Unfortunately, the current climate across much of the state involves high soil temperature, high light intensity and rapid drying of soil.

“This can be a problem for gardeners because achieving a full stand of plants in these extreme weather conditions may require special treatment,” he said. “Gardeners may have to employ strategies such as shade row covers when seeding, along with supplemental watering to reduce soil temperature to aid in seed germination.”

Vegetable seeds are also vulnerable to the hot soil surface exposed to the summer sun.

“In order for viable seeds to germinate or sprout, they must have the proper temperature, adequate moisture and sufficient oxygen,” Hillock said.

Shade row covers can be made from burlap and a few stakes, said Laura Payne, horticulture specialist in the OSU Extension Payne County office.

“The burlap still allows light through but diffuses the heat on the tender plants,” Payne said. “Gardeners can also use screen wire strips or boards to cover the rows, which will moderate both soil temperature and soil moisture. Remove the covers after the seedlings emerge.” Another option to help stave off the heat is creating deeper furrows in which to plant. This allows the seed to germinate in cooler soil. Even then, gardeners will need to supplement with extra irrigation to ensure the soil remains moist at seed depth.

Season extension methods, such as high tunnels or hoop houses, will help, especially if planting is delayed a few weeks to avoid excessive heat.

While daylight hours are still very warm this time of the year, nighttime temperatures are slightly cooling off, allowing plants to recover in the evening. Payne said the cooler evening temperatures will help with the establishment of a fall garden, but once seeds are sown, irrigate adequately. A garden‚s soil dries out quickly during the day.

Gardeners who use transplants should condition them by reducing the amount of water supplied and exposure to full sunlight. Hillock said this process can take three to five days.

“When you‚re ready to plant the transplants, do so in the late afternoon or early evening when it‚s cooler to help reduce transplant shock,” he said. “Water the plants as they are set. A water-soluble fertilizer can be used if necessary.”

Typical fall vegetables to plant include broccoli, leeks, onions, peas, radish, kale, cabbage, collards, kohlrabi and cauliflower.