Saturday, 11 February 2017

Heatwave Survival for Plants

When the temperature is soaring like it has recently it's often hard to think past our own discomfort, but we have to be mindful of our plants too at this time.

It seems fairly basic advice but we need to protect our plants as much as possible during these major heat events. We have to give our plants the very best advantage against the extreme conditions.

Plants naturally evaporate water from the underside of their leaves, releasing this moisture with oxygen as by-products of their photosynthesis. In very extreme heat events, this evaporation process speeds up therefore they consume more water, so they need to take up more water from the soil. In high heat situations, water is also evaporating from the soil at a greater rate and so the poor plant mightn't have sufficient water resources to make up for the increased expiration. 

If your plant gets really dry, the more likely damage will be to the plant cells. This then makes your plant more susceptible to at the very least, sunburnt leaves or even its demise. There are obvious signs of heat damage:

  • Wilting - this is one of the very first indicators that the plant is suffering. As the plant tries to decrease the surface area exposed directly to the sun.
  • Dropping leaves - If the stress to your plant increases, it may even drop some of its leaves. This reduces the plant's area that water can evaporate from, therefore conserving the moisture it has got available.
  • Dropping flowers or fruit - If your plant is flowering or fruiting, it will also prematurely drop its flowers or fruit. To produce flowers and fruit a lot of a plant's energy is needed, so shedding these during extreme conditions is one way the plant employs to protect itself.

Some basic tips on how to protect your garden during heatwaves:

Be Prepared

Apply as much water as you can in the evening or morning before the temperature rises. 

Take special care of potted plants and young seedlings. Erect some temporary shade (like old sheets, beach umbrella, shade cloth etc) or spray with Yates Waterwise Drought Shield or AgroBest Envy on to very vulnerable plants. These products give the plants a polymer layer that provides protection from heat, salt, wind and also water loss. I have tried a polymer product on some Hydrangea plants which have generally suffered on really hot days, even dropping their leaves and it worked a treat.

Potted Plants

Move your potted plants into a shaded area if possible and water them well. During these big heat events it is perfectly OK to keep pot saucers filled with water, as the plants can draw on that water over the day. If you are preparing pots for exhibit in the Coffs Show in May it is vital that you pay particular attention to protecting them from heat stress and damage.

Water effectively

Start by checking to see if you really do need to water - push your finger through the mulch layer and check to see if the soil is moist. If it feels dry, it's definitely time to give it a drink. Give it a good deep watering so the water penetrates into the root zone. This is preferable to short, surface waterings that only encourage the roots to stay near the surface where they're more vulnerable to moisture loss. Also be mindful not to use a hose nozzle that delivers a strong jet that gouges holes in the soil. Instead choose a sprinkler or a water wand that is a gentle shower (or water breaker as sometimes called) to water gently. An application of soil wetting agents around the root zone in garden beds and also on potted plants will help get water where it is needed by breaking down the waxy water repellent layer that can develop on soil surfaces and potting mix making it hydrophobic.


Mulching material really should have been applied long before the heat event. It is best to apply a good layer of mulch when the ground is already moist and then further water applied after mulching. This will keep the soil cool and protect it from drying out in extreme heat. If your pots haven't been protected yet you could add some mulch now. Water the pot well, apply your mulch layer, then water again.

Water storing crystals

If you really have to plant something when there is going to be extreme heat it is best to give the poor thing the best start possible by using water storing crystals. Start off by soaking them in water so they swell before digging them into the planting hole. You may have made the mistake that many make and placed them dry into the planting hole without pre-soaking. The plant has been duly well watered in and later you find that your newly planted cherub has 'popped' out of the ground when the crystals took up the water and expanded!

Post event watering

After the heat has abated, give your plants some organic seaweed preparation (eg Seasol) to help them 'bounce back' after the heat event. It is not really a good idea to do this during high heat as the leaves might burn.

Be neighbourly

If your neighbour is away or is elderly, take time out to assist them by doing some watering too. Sometimes when it is very hot people flag very easily and are unable to get out and do this basic care.

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