Minimising stress over summer

Article originally published by: Kiwi Gardener

The hot sun beating down on plants can have negative effects, encouraging Michael Unverricht to share his tips for a cool counterattack.

Wilting and flagging leaves on a hot summer’s day is a sign of heat stress. Heat stress can be prevented by an adequate supply of water directed to the soil. This will assist summer plants to replace moisture lost through leaf transpiration, which is the evaporation of water from the leaf surface. Transpiration is the method plants use to cool themselves. It is calculated that around 80% of the water that is absorbed through the roots during a hot summer’s day will be used for cooling purposes. Therefore, an adequate amount of water must be provided to prevent wilting and long-term tissue damage. The cool of the evening will see the wilting leaves and flowers return to their natural position. However, continued summer heat stress will have a profound influence on the development of the plant and may cause irreversible stem damage to the plant. Prolonged heat stress will see the leaves slowly turn brown and fall off the plant.

Lettuce plants require continuous moisture to flourish in the hot summer.
he fuchsia has suffered from moisture loss. It will recover if it is soaked in a container of water. Future growth and flowering will be delayed due to a temporary lack of water.


  • Add compost to the soil before planting. Compost has moisture-retentive properties providing moisture to the plant roots.
  • Mulch around shrubs and trees as mulch lowers soil temperatures. Lower temperatures will decrease the loss of moisture due to evaporation from the soil.
  • Place the plants according to their needs. The delicate coloured flowers of hydrangeas will get sunburnt if they are grown in sunny positions.
  • Provide partial or temporary shading for a plant that is suffering from being planted in the wrong position.
  • Consider using a soaker hose. The soft rubber tubing has tiny holes through which water slowly drips when the tap is turned on. Bury the soaker hose under the row of lettuce or under the mulch. Since the soaker hose is flexible, it is easy to manoeuvre amongst plants.
  • Consider a drip system attached to a length of polyethylene piping. Drippers are attached to the piping at the base of each plant. I believe the dripper system is the most economic form of watering as the method targets the roots and does not waste water on open spaces of the garden. The more upmarket drippers have an adjustable head that can control the amount of water released.
  • Build a raised wall of soil around the plant. Water poured into the saucer-like depression will seep downwards and not run off. 
  • Water in the evening. The water has time to be absorbed into the soil before the heat of the following day. 
  • Give lawns a deep watering – if possible. A five-minute sprinkle of a lawn is a waste and will only keep the lawn roots close to the surface and in danger of being cooked by the sun. Sprinkle the lawn for 15-20 minutes to ensure a sufficient penetration of water. 
  • Revise your garden plan and add tall trees and shrubs to create shade and provide wind protection. Hot winds, rather than the hot sun, do the most damage. 
  • Use shade cloth and windbreak material to provide temporary shade.
Heap up the soil around the stem of the plant creating a saucer-like depression. Pour water into this depression to save wasting run-off.
The fine spray of water from the soaker hose provides deep watering under vegetable plants. The tubing can be tucked under mulch among flowering perennials.


  • Apply water to wilting leaves on a hot sunny day. The spots of water act like magnifying glass and may burn spots on the leaves.
  • Use sprinklers during the day. Not only is the danger of sunburn present, but also water on leaves can make plants more susceptible to diseases. Sprinkler watering encourages snails and slugs due to the moist soil environment.
  • Waste water. It is said that only one per cent of the world’s water supply is drinkable and available for living things.



  • Planting vegetables and shrubs in large pots. In hot weather the pots can be moved into sheltered and shaded areas.
  • Adding water crystals to the pots. Their presence increases the moisture-bearing capacity of the soil.
  • Add a better watering system – improving your sprinkler or drip-irrigation systems will mean you can water more efficiently and reliably.
  • Replant your garden with heat-tolerant plants. Look around the neighbourhood and see what plants, both exotic and native, are doing well.
Give summer plants a head start by filling the planting hole with water. This provides a reservoir of water beneath the plant. Allow the hole to drain and then plant.
Remove the bottom of a 1.5L drink bottle. Dig a hole at an angle to the trunk and insert the neck of the bottle as far as possible towards the roots. Filling the bottle will take water directly to the roots.