With high temperatures predicted for many areas of mainland Australia this week, I would like to remind you that you can find tips on helping your garden to survive extremely hot temperatures here: Heat wave protection
Heat wave help
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Tag Archives: heat wave
Heat wave protection
Some parts of Australia are enduring extremely hot weather and, apparently, there is more to come this summer. Periods of intense heat can cause scorching in many gardens.
Although European-based garden texts recommend full sun for most vegetables, where summers are hot and air pollution is low, full sun can result in sunscald. While Australian natives have evolved to restrict loss of water through leaves in hot, dry conditions, very hot plants, especially those that originated in cooler Northern Hemisphere regions – such as most of our vegetables and fruits, lose a lot of water through their leaves in an effort to keep cool, in a similar way to humans perspiring.
A bit of shade
Providing some light shade during the hottest part of the day can prevent sunscald on susceptible crops, and, by keeping the plants cooler, reduces their water consumption, an important consideration where water restrictions apply. We use lightweight, knitted shade cloth, supported by arches made from 38 mm irrigation pipe attached to garden stakes or star stakes, or you can use old light-weight curtains or sheets.
Each canopy is positioned to allow morning sun to reach plants, yet not restrict air flow around them. Poor air flow (such as in fully enclosed areas) can produce conditions suitable for some fungal diseases to establish. Instructions for making these can be found in the post Sun and heat protection.
However, in an emergency, any old curtains or pieces of lightweight fabric will do. Tie the corners to garden stakes to provide some relief for garden beds during the hottest part of the day.
If possible, move potted plants to a shaded area of the garden, and group them together. This provides more humidity around the plants, and reduces their water requirements.
Water is essential
Adequate soil moisture is essential for your vegetable garden to maintain good growth during heat waves. Mulching garden beds is very helpful. A method that we have found very helpful to water mulched beds is to use plastic soft drink and juice bottles to funnel water directly to the root area of susceptible plants. This is a quick and very efficient way to hand water during water restrictions, heat waves or windy weather. Limp tomato seedlings will freshen up in about 10 minutes after watering by this method.
Simply cut off the base of each container, remove the lids and bury the necks of the containers about 8 cm deep near outer edge of the foliage of plants. Large shrubs may require several containers. Pour water into the container until it begins to drain slowly – an indication that you have dampened the soil in the root area.
Seedlings and pot plants are usually the first to suffer during heat waves, and you can find advice on how to revive stressed pot plants here: Pot plant stress
Water for wildlife
Don’t forget to provide water for birds and bees that visit your garden. A bird bath, or containers of clean water positioned where cats and dogs can’t reach them will provide relief for the insect-eating birds and the bees that pollinate your crops. Chlorinated pool water is toxic to these helpful creatures. A container of water under shaded foliage will be appreciated by your resident frogs too.
Coping with heat waves
Heat waves place extreme stress on gardens when plants lose lots of water through their leaves in an attempt to keep cool and retain humidity around their foliage. You can help reduce moisture loss by providing some temporary shade over sensitive plants in the vege patch and ornamental parts of the garden.
See also: Sun and heat protection
However, seedlings and pot plants are usually the first to suffer in heat waves, and these may need watering twice a day until weather returns to normal. If potting mix dries out, the first sign may be complete collapse of a plant. If you water dry potting mix in the normal way with a hose or watering can, your plants may not be getting as much water as you think. This is because potting mix shrinks slightly when it dries, leaving a narrow gap between the mix and the pot. When you water, most of it runs into the gap and out through the drainage holes, leaving the mix around the roots still dry. Seedling punnets and smaller pots can be thoroughly watered by immersing the entire pot in a bucket half filled with water, or use a laundry tub if a lot of pots need reviving.
Water should come over the top of the pot. Leave the pot in the water until bubbles cease to rise. Short term immersion won’t hurt the plants. Then lift the pot allowing it to drain into the container. This method of watering also works very well when your water supply for plants is strictly limited.
For pots too large to be immersed in a container, fill some large soft drink or juice containers and insert 2 or 3 neck down into the potting mix. Provide support if necessary and allow them to empty slowly into the mix. Re-fill the bottles and repeat watering until water is being drawn into the mix very slowly. If heat is likely to continue for some time, place some mulch or stones on the surface of the potting mix to slow evaporation.
Heat wave first aid
A lot of Australian gardens are suffering from a prolonged spell of very hot dry weather.
Garden beds that contain a moderate amount of organic matter will handle the extreme conditions better than most, as organic matter in soil keeps soil more moisture retentive, especially if mulch is also applied to the soil surface.
• Avoid watering in the middle of the day. Water early or late in the day. If watering in the afternoon, first check that the water in the hose has not reached a temperature that will scald plants.
• Try to give vegetable beds and precious shrubs a deep watering rather than a light daily hosing, and only repeat watering when the top cm. of soil becomes dry. Daily hosing usually only wets the top centimetre, or so, of soil, encouraging plant roots to stay close to the soil surface, making them more prone to wilting in hot weather.
• Apply a thick layer of mulch to all beds, if possible, as this will prevent loss of soil water through evaporation. However, avoid mulching beds close to buildings in areas where bush fires are a risk.
• Provide a temporary shade canopy for beds or plants that appear stressed. Use whatever is available – shadecloth, tarpaulins, old curtains, etc. Shading them will reduce water loss through the plants’ leaves, and plants will require less watering. Plants release moisture through their leaves in an effort to keep cool, in a similar way to our perspiration.
• If possible, move potted plants and seedlings against the south side of a building, where it is cooler. The mix in pots can become much hotter than soil in beds, and potted plant roots can become permanently damaged in this type of weather.
• Place pots close together as they will create group humidity, keeping them cooler.
• Avoid fertilising in this weather, unless it is seaweed tea applied after a deep watering. Fertilising when soils dry out quickly increases the risk of fertiliser burn and makes plants less able to cope with adverse conditions.
• While you can leave burnt foliage on plants and the plant will usually recover when temperatures cool and watering is adequate, if a favourite evergreen shrub or citrus tree is extremely distressed, prune it back – leaving some foliage so that it can manufacture food. This can help the plant to provide water more efficiently to the remaining plant. Leave the prunings as mulch around the base of the plant. However, pruning of deciduous plants at this time of year can cause excess sap loss (bleeding) in some varieties, such as grapes, pecans, mulberry.
• Give flowering annuals lower priority if water is restricted – these can be easily replaced when conditions are more suitable for growth.