Heatwave! How NOT to push your veg to the edge

When the summer temperatures reach the thirties and well above, we can usually retreat to the safety of an airconditioned room. But our plants are stuck outside, and often need our help to survive.

© Scott Hitchins 2015

This applies especially if we are expecting to eat them.

When helping our edible gardens to beat the heat, we are aiming to achieve six things:

  1. Shade the plants from the sun so that they continue to grow.
  2. Protect the plants from drying heat and winds
  3. Ensure that the part of the plant which we eat stays sweet and firm; not limp, bitter and sunburnt.
  4. Protect the beneficial soil microorganisms from heat and UV radiation.
  5. Keep the soil moist to maintain its structure.
  6. Growing plants which cope better.

Shade

Shade can be as simple as throwing a bed sheet or an old curtain over your veggie garden until the heat has passed. If it’s a bit windy, consider weighing the edges down with some rocks or bricks or even clipping it to the plant with some clothes pegs. Leafy branches pruned from trees also do a pretty good job in a pinch. These work well if we haven’t had time to get organised, but as it seems that heatwaves are going to become the norm, rather than just a freak occurrence, it’s worth investing in some sturdier structures and shade material.

Knitted shade cloth is relatively cheap, long-lasting with excellent UV stability and also works as a wind break instead of a sail due to its porous nature. It is available in several grades, from 50% UV protection, up to 90%. If you intend to leave the shadecloth up all summer, as you might over your nursery area, then 50% shade is the right stuff as it lets enough light through for delicate seedlings and cuttings. For the main veggie garden where you are just putting up the shade when extreme heat is forecast, any of the grades will do the job, with any scraps or off-cuts being handy for isolated shrubs and young fruit trees. For those of us who don’t mind doing a bit of recycling and dumpster diving, large building sites are often a source of huge amounts of free shade cloth which they use on their security barriers: I’m keeping a close eye on my local shopping complex which will have hundreds of metres of printed blue shadecloth to dispose of when they finish their rebuild.

Structures

These can be as simple as some tomato stakes with the shadecloth held on with bulldog clips borrowed from the stationery cupboard or you can make lower hoop structures with PVC conduit or similar bendy stuff. On the more permanent end of the scale, you could build a light weight structure out of bamboo, tent poles, aluminium rod, timber stakes etc and cage your garden bed area: My main veggie growing area consists of two wicking beds, half a metre apart. Each is 1.5m wide and 6m long. The whole thing is caged to 2m high with scrap aluminium lengths from a shopfront roller-door that I pulled out of a skip. It is permanently bird-netted and I cover it with shadecloth during hot spells. An even longer term, but more aesthetic, solution is to plant deciduous trees, shrubs, vines or hedges on the west side of the garden to block the hottest of the summer sun but let through the gentler winter sun.

Protection from drying winds

Wind often causes more damage to plants than the sun itself: A hot dry wind will evaporate moisture from within the leaves far faster than the plant can replenish it via its root system, leaving nothing but curled and crispy brown leaves. Again, shadecloth makes an excellent windbreak, taming the wind instead of creating turbulence as a solid fence does. Map out which direction the hot winds attack your garden from and build or plant barriers.

Protect the edible parts

Simpler forms of shading include putting cloth bags over individual ripening fruit: Tomatoes and grapes in particular, tend to suffer from sunburn, leaving tasteless white patches on the skin. This has the added bonus of preventing birds from getting at your fruit and has no effect on ripening, which relies on heat, not on sunlight.

Protect the beneficial soil organisms and…

…keep the soil moist to maintain its structure. Apart from protecting the plant, it is also vital to protect the soil from heat, UV radiation and drying out. Millions of beneficial fungi, bacteria and other microorganisms interact with your plants through the root system, enabling the plant to access soil nutrients in an absorbable form and helping to develop soil structure with humus development. These little life forms are much more sensitive to heat and UV than the plant itself. The obvious answer here is adding organic matter, but when, what and how are important questions: Decomposed organic matter (compost and old manures) should be added to the soil prior to planting. This enables the soil to retain much more moisture, with organic matter being able to hold up to its own volume in water. After planting, a protective layer of fine mulch will insulate the soil and prevent UV radiation from reaching our microscopic friends. Mulch with such things as sugarcane, straw or dried lawn clippings in the veggie patch, keeping woodchips and other coarse mulches for paths and around trees.

Soils which have dried out can become water repellent and require a wetting agent to allow water to penetrate instead of running off. There are several commercial varieties available, but just swishing some natural soap in a watering can will do the job just as well. Avoid pine-based mulches which can often create a waterproof waxy coating on the soil particles.

Grow plants which cope better

Time for a bit of horticultural Darwinism: when you save seed each year, save it from those plants which have coped best with the conditions in your garden. A lot of our veggie seeds have been imported from Europe and the UK and then sold to you as seedlings grown in temperature controlled green houses. What hope do they have in a Melbourne heatwave? Try to buy locally produced seeds and seedlings and don’t forget to swap with local friends and neighbours. Try Googling Eden seeds, New Gippsland Seeds and bulbs and Diggers to start your own selected genetic line.

Watering notes

Watering in the morning or evening is the most efficient as the water will soak in before evaporating. However, if your plants are wilting and drying out during the day, you don’t have to wait until the evening to water them, it may be too late: It is not true that watering in the sun can burn the plant. Remember: The life you save may be your dinner! Gardening books often talk about a long deep watering once a week, being the best for our garden. While this is mostly true for trees and established perennials, it certainly does not apply to your annual veggies whose roots have had little time to grow and develop. During a heat wave, watering may be required once or even twice a day. Make sure that you are watering the soil and not the leaves: Leaves left damp overnight in warm weather are very susceptible to mould and mildew shortening the life of the plant.

Other tips

  • Reduce your lawn size: Lawns take as much, or more, water to maintain than an edible garden, but they don’t taste as nice. If you must have a lawn, let it grow longer (8-10cm) to shade the roots and soil. Many people end up in the bizarre situation of having to be out in the hot sun, getting burnt, mowing a lawn they don’t use.
  • Store water in the soil: Consider diverting downpipes into dips, soaks, swales and channels to give it time to soak into the soil instead of running off down the drain.
  • Perennial veggies such as asparagus, artichokes, rhubarb and many others live long enough to establish deep, extensive root systems that tap into subsoil moisture.
  • Potted plants can be grouped together to create a cooler, shadier microclimate and can also be moved to shadier areas.
  • Don’t forget the wildlife: Provide a clean and reliable source of water in a birdbath and /or pond. You will be repaid with avian entertainment, free pest control and regular deposits of fertiliser. You will also attract predatory bugs, bees for pollination and, if you are lucky, some froggy friends to devour slugs and snails.