Heatwaves are part of the Australian summer, where we get days on end of temperatures over 38°C. If this is accompanied by winds and warm nights, it can put your vegetable garden into stress and even cause a few fatalities. The best way to protect your vegetable garden from heat is to prepare the soils well, have a good watering routine in place – and provide shade on extreme days.
Chances are if you are reading this, there is a heatwave coming and you are wondering what to do, so here we go – how to protect your vegetable garden from heat:
Establishing a routine of regular deep watering in your garden encourages strong root development, and a reduction in surface dwelling roots. Ideally setup your garden with drippers underneath the mulch, so all the moisture is in the root zone.
When we are experiencing a heatwave, you will need to switch from watering 2-3 times a week to watering daily, sometimes twice a day for anything in pots or softer plants like lettuces.
On extremely hot days you should water deeply the night before or early in the morning, before the sun hits the garden.
After the sun has gone down, you can also water the leaves to immediately reduce the build up of hot air, but don’t make a habit of this as you can end up encouraging fungal diseases. If you are using shade covers, open these up at night to clear the hot stuffy air and hose off the leaves. This helps with creating a cooler environment for the vegetable garden, so the normal plant process of transpiration can work more effectively.
Mulch provides a physical barrier between the soil and the elements, it insulates the roots from heat and helps prevent moisture from evaporating. Use a thick layer of pea stray, lucerne hay or sugar cane as mulch – around 7cm thick, but keep a little away from the plant stems for best results.
If you don’t have mulch on hand, use layers of newspapers (just wet them down after and place some bricks on top so they don’t blow away). Other short term options are to use slabs of the yellow pages (sorry Sensis, we are all online now) or sheets of cardboard (from all your online delivery boxes).
The aim is to retain moisture and provide shade on the roots, so focus on that goal and not the aesthetics for now.
Cover your garden with pieces of shadecloth, tablecloths or old bedsheets. Try making tents out of cardboard, or move your patio umbrella closer to your beds. A 50% white shadecloth is recommended to keep plants like Tomatoes flowering and growing, but you can use 70% green or black over more delicate crops like salad leaves and soft culinary herbs.
The shade is designed to both protect from sunburn on the leaves and fruit, and also to reduce the immediate temperatures around the plant – we are trying to create a cooler micro climate within the garden beds.
Again, forget the aesthetics for now. Who cares if your garden looks like a kids cubby house, we are focusing on survival here…
Anything in a pot needs to be moved to a full shade position, or even brought inside for a few days. Potted plants can collapse pretty quickly as the roots heat up as well as the plant itself.
I think that lots of Australians are starting to think through their Summer bed position vs their Winter beds, or at least growing crops in different locations to allow for some afternoon shade in Summer.
If a crop requires 5 to 6 hours of sunlight to successfully grow, this is easily achieved between 8am and 2pm in Summer, with shelter provided from the burning afternoon sun. You can place a bed behind a Eastern facing wall to achieve this, or if you know your garden well choose a spot that will be sheltered by a tree in the afternoon.
You can also place a permanent shade screen of 50% white shadecloth on the western facing side of the garden, so that it is protected late afternoon.
4. Harvest Crops
Regularly go out and check your plants, collect the eggplants , tomatoes, cucumbers etc so that your plants don’t have the added burden of supporting fruit growth.
Remember the plant has a vascular system that is working very hard to pump water around all the stems and leaves, so anything you can do to reduce that effort the better. This means that available moisture in the soils can be drawn up and used for transpiration to keep the plant cool.
5. Organic Matter
OK I know this doesn’t help you in the short term, but having healthy soils with high amounts of added organic matter makes a world of difference to moisture retention. Sandy soils drain too freely and clay soils can become hydrophobic. The ideal soil is a loam that has loads of organic matter to act as a sponge.
Building up your soils is a never ending task in the vegetable garden, as each crop takes nutrients from the soils and over time matter decomposes – you just have to keep adding compost, leaf litter and manures.
Summary: how to protect your vegetable garden from heat
- Water the night before a hot day – deep watering for the roots, and after a hot day spray down the leaves to reduce built up hot air
- Use a thick mulch of straw to keep moisture in, and reduce heat on the roots
- Provide shade any way you can
- Pick crops every day
- Keep working on improving your soils