Care for lawns during periods of extreme heat.
When a plant, irrespective of whether it is your prize pelagonium, or just a single grass plant in a lawn, suffers heat stress, many of the fine hair roots fall away from the root system. This is the plant’s normal response to stress, when biological functions shut down and leaves begin to wilt. It takes a long time for the plant to recover from this kind of stress. Growth tends to be weak and spindly because those fine roots that account for much of the root system surface area have been lost. We see this in hydrangeas, in fuchsias, and in turf grasses that receive a daily sprinkle rather than deep watering. The shallow root zone is unable to cope with extra demands for soil moisture.
The only way that the plant will recover is to keep the soil temperature down to the optimum for that plant where maximum growth will occur and by maintaining humidity about the leaf zone.
Under extreme temperature conditions it is acceptable to apply overhead watering to cool the plant. But overhead watering in more moderate temperatures may cause infection by fungal pathogens such as black spot and downy mildew.
Four and seven-day weather forecasts make it possible to care for our gardens more efficiently. Ornamental shrubs and turf plants will survive heat better if the soil has had a deep soaking down to the root zone 24 to 36 hours before the temperature soars above 32oC.
While kikuyu grows best in temperatures from 15oC to 30oC, a protracted spell of hot weather over 35oC will allow soil temperature to build up and force the plant into dormancy. The best management practice is not to let the soil temperatures rise above a critical 32oC by thoroughly irrigating when the weather forecasters first predict a heat wave, four or five days before the heat occurs.
While we can’t control Nature’s heat, we can lessen the effects of heat stress by temporarily raising the mowing height to provide a denser canopy over the soil surface. Turfgrass that is under drought stress should be carefully maintained. It is best to raise the height of cut and not mow during the heat of the day. Rotary blades should be kept sharpened.
You may be questioning the wisdom of continuing to maintain a lawn given the recent increases in the price of water. Remember, some of the environmental benefits of lawns include lowering the temperature of the surrounding environment. This can result in a direct saving in air-conditioning costs. Also, a well maintained lawn can increase the value of a property by up to $15,000.
Crab or Summer grass will respond to selective herbicide treatment. Selected ALMA lawn contractors are able to apply the specialist weedkillers required. A troublesome weed of lawns and gardens, summer grass can produce enormous quantities of seed. United States workers have counted 150,000 seeds from a single plant.
Vegetables: Blossom end rot of tomatoes is caused by a sudden change from abundant water to drought during hot weather. This usually happens when the plants have dried out and are stressed, and then over-watered. Fruit drop in melons such as pumpkin and cucumber is often induced by over watering during a cooler spell.
Give roses a light summer trim to encourage an autumn flush of flowers. Lightly fork in a dressing of Blood & Bone fertiliser and additional Potash or use Potassium nitrate fertiliser on its own.
Pests and diseases: As the weather becomes more humid aphids become active, feeding on new plant growth. The most effective insect control is weed control – aphids breed on many species of thistle and other preferred weeds, then transfer to the young shoots of ornamentals.
Lady beetles help in control of aphids
Although pesticides are one management tool, a complete reliance on chemicals is not necessarily the best method because of potential resistance, secondary pest problems and economics.
Ladybeetles will devour up to 50 aphids a day as well as help control scale, mealybugs, and leafhoppers.