How to Keep a Garden Alive Through a Heatwave

A run of hot days will undo a lot of careful work in a garden, and the frustrating part is that most of what saves a patch in a heatwave has to be done before the heat arrives rather than during it, because once the soil is dry and cracked there is only so much a hose can put back in a morning.

None of this is complicated. It is shade, water at the right time of day, and a decent layer of mulch, and those three between them carry a garden through the worst of a South Australian summer far better than standing out there with a hose every evening does.

Shade takes the edge off

Plants that are perfectly happy at 28 degrees will scorch at 40, and the easiest fix is something between them and the afternoon sun. Shadecloth stretched over a few stakes or star pickets works, an old sheet works, and a couple of sheets of lattice leaning against the western side of a bed works.

Prop it up so the air can move underneath. Cloth lying flat on the leaves traps heat against them and you end up worse off than you started, so leave a good gap between the fabric and the plants.

Shadecloth comes in different densities and it matters more than people expect. Around 50 percent is right for vegetables that still need decent light, and 70 to 90 percent is for seedlings, ferns and anything that is really struggling.

Water early, and water deep

Early morning is the best time, because the air is cool, less of it evaporates before it gets down to the roots, and the plant goes into the heat of the day already full. Watering at lunchtime wastes most of it and watering at night leaves the foliage damp for hours, which is how fungal problems get started.

Give it a proper soak rather than a quick pass with the hose. A light sprinkle wets the top couple of centimetres and encourages the roots to sit up near the surface where they cook, while a deep water sends them down where the soil stays cooler for longer. A soaker hose or a run of drip line does this better than you will by hand and it does it while you are having your coffee.

Aim at the base of the plant and not over the top of it, because wet leaves in full sun mark and burn. Pots and hanging baskets dry out much faster than a garden bed does, so check those twice a day when it is hot rather than once.

Mulch is the one that does the heavy lifting

A thick layer of mulch keeps moisture in the soil, keeps the soil temperature down around the roots and stops the surface going hard and water repellent. Pea straw, lucerne, sugar cane and bark chips all do the job, and the main thing is to put down enough of it, which means a good 50 to 75mm, not a light dusting.

Keep it back a couple of centimetres from the stems so the base of the plant is not sitting in damp mulch, and top it up when it breaks down, because it does break down and that is half the point of it.

If the soil has already gone water repellent and the water is beading up and running off instead of soaking in, a wetting agent will fix that before the mulch goes on. There is no sense mulching over soil that will not take water.

Some plants are simply built for it

Tomatoes, zucchini, capsicum, chilli, eggplant, okra and pumpkin all handle real heat, and so do most natives and the drought tolerant exotics. Lettuce, spinach, coriander and anything else that bolts in a warm week is always going to be hard work in an exposed spot, so give those the morning sun and afternoon shade if you want them through summer at all.

Reading heat stress

Wilting in the middle of the afternoon is normal and usually not a problem, since a lot of plants close down and droop to save water and pick themselves back up once the sun is off them. Wilting first thing in the morning is the one to act on, because that means the plant genuinely has nothing left.

Scorched brown edges, bleached patches on the leaves and flowers dropping before they set are all heat damage, and the answer is the same in every case. Get some shade over it, water deeply at the roots and leave it alone for a bit.

Go easy on the feeding

A plant under heat stress is not in a position to use a heavy feed, and pushing nitrogen into it produces soft new growth that burns straight away. A light seaweed tonic is the safer choice in a hot stretch, since it helps with stress tolerance rather than forcing growth, and the proper feeding can wait until the weather backs off.

If you are not sure whether what you are looking at is heat stress, a watering problem or something else entirely, bring a leaf in and show us. That is a two minute conversation over the counter and an hour of searching otherwise, and there is no video that can look at the actual thing in your hand.

Shop related products

• Martins Organic Sugar Cane Bale 11KG. Fine mulch that breaks down into the soil and is easy to spread around vegetables.
• Pope Drip Eze 13mm x 30m. Drip line to run along a bed so the water goes in at the roots.
• Pope Simple Set Tap Timer. Set it to come on early and the watering happens whether you are up or not.
• Pope Hold Down Stakes 10 Pack. Pegs to keep the drip line where you put it.

Did you know we also stock shadecloth by the metre in 50, 70 and 90 percent, pea straw and lucerne bales, soaker hose, wetting agent crystals and Seasol seaweed concentrate in the shop. Not all of it is on the website, so give us a ring on (08) 8536 4333 to check what is on the shelf.

The mulch, the irrigation fittings and the rest of it live in the garden centre at H, and there is more of the watering range in the Pope section if you are putting a system together.

Keep reading

• How to Water a Veggie Garden in Summer Heat
• Heat Tolerant Vegetables: Ten to Grow in a Hot Summer
• How to keep flower beds alive through a heatwave

Cheers,

Candeece

I am the person who plants the thirstiest thing in the hottest corner and then acts surprised in January, so take the advice rather than the example.