Hot and bothered
Solutions to gardening issues caused by the stresses of summer weather
RAIN AFTER DROUGHT
QEven though it’s dry now, we tend to get some big storms over summer. What is the best way to manage the soil after an unusually heavy rain event? Should we feed it? If so, with what?
AYou might not need to do anything except check that the rain has wet the soil enough to skip that day’s watering. Keeping a good layer of mulch over soil helps to reduce damage caused by rain.
The impact of heavy rain depends on how heavy it is. Compaction can be an issue, from the pounding rain, and from you moving around on the wet soil and lawns. Once the soil has drained and is no longer saturated, aerate it a little using a garden fork. Just plunge the fork into the area to make holes, trying to avoid roots.
Nutrients can leach from soils after extended rain events. Nitrogen is the major one, but it is also added by rain that falls during a thunderstorm, which can balance it out. If any plants show obvious yellowing of older leaves after a rain event, it’s a fair indication that they need added nitrogen. If there are no obvious signs of stress, save your money. For a fast-acting feed, apply any balanced all-purpose fertiliser, and water in well. Liquid foods give the fastest results, and should be followed by an application of a granular plant food. Natural compost and manure are slow-release options.
TOO HOT TO SPRAY
QWe have been told to treat scale on citrus and gardenias with an oil spray, but it can’t be applied during really hot weather. What should we do?
AOil sprays can burn citrus and gardenia foliage when the temperature climbs above 35°C. In extremely hot weather, wait until the cool of the late afternoon to apply an oil-based spray, then leave it overnight. Put a reminder note on the fridge to wash off the oil first thing in the morning, before the temperature rises again.
BURNT PLANTS
Q ALast summer, I came home after a scorching day to find plants burnt. How can I help them, and stop it happening again?
Foliage burn is heartbreaking, but many plants recover from it. Start by watering the foliage to cool the plants down, then soak the ground around them. If you’re expecting more extreme weather, or if it’s still hot, erect a temporary shade structure by laying old sheer curtains, shadecloth or whatever you have over the plants. Make sure the protective cover can’t be dislodged by wind.
Anti-transpirant sprays reduce foliage burn by providing a temporary protective coating, without impeding the plant’s growth.
Wait for the hot weather to abate, and for the plants to show signs of recovery, before feeding or pruning them.
For the summer ahead, make a note of plants that are likely to suffer, and be ready to protect them. Watch the weather forecast, and water plants
well before the heat arrives. Also, shade vulnerable plants before leaving the house.
Longer term, consider whether there’s a better spot in the garden for plants that repeatedly suffer from foliage burn over summer. Look for a position that’s going to offer more shade and protection during the hot summer months, even if it’s sunny at other times. Move evergreens during autumn or winter, but wait for deciduous trees to be fully dormant in winter before moving them to a better location.
HEAT FROM BLOCKS
QMy raised garden beds are made from two layers of perforated concrete building blocks. The vegies thrive, except in summer. Is the heat from the blocks causing some of them to fail? If so, what can I do?
AYes, it’s likely there’s a build-up of heat from the concrete blocks. You’ll see the effects of this mainly around the edges of the beds. Covering the blocks with trailing plants, or even painting them white, might be enough to reflect the heat and reduce burning.
Another issue to consider is the depth of the raised beds. Two concrete blocks stacked makes beds approximately 40cm deep. Beds of this depth will dry out much faster in the heat than beds only one block high, because it takes more to wet the deeper layers of soil in a taller bed, and the evaporation rate is greater.
A simple option is to reduce the bed to one block high, then use the extra blocks and soil to make another bed. If you want to maintain a bed of that depth for physical reasons, consider converting it to a wicking bed (see page 50 of the October 2019 issue of ABC Gardening Australia magazine). Or you could add a soil-wetting agent, keep the soil surface shaded with mulch, and reduce the amount of direct sunlight that reaches the bed in summer.
KEEPING SOIL COOL
QApart from mulching, what is your recommendation for keeping garden beds healthy during the 40°C heat we experience in a Canberra summer?
AIn beds where you’re growing tough plants that are well adapted to your local conditions, seasonal extremes are fine, and the plants will cope, so there’s no need to do anything extra to protect them. Issues occur when you’re growing plants that can’t cope with these extreme conditions, such as cool-climate ornamentals.
There are three main things that can be done to keep soil cooler and make a huge difference to the wellbeing of plants. The first is regular watering. Water helps keep both the plants and the soil cool, so be sure to water regularly, especially when hot weather is forecast.
In the lead-up to very hot weather, use products that help to strengthen plant cells and protect plants from extremes. Liquid seaweed watered over the plants and soil strengthens the cells of plants, while an anti-transpirant sprayed on the foliage of susceptible plants reduces moisture loss and stops them drying out too quickly.
In small areas, erect temporary shade over sections of the garden where plants – both ornamental and edible – are likely to suffer. This is a labour-intensive job, but it’s an option. For a longer-term solution, consider planting a shade tree or screening hedge, or constructing an arbor to support a climbing plant, to provide plants in that part of the garden with summer shade.
TRANSITION TIME
QWhat should a vegie gardener do at the end of the season? Some things are still healthy and growing in my garden at the end of summer, while others, such as capsicum, eggplant and tomato, are on their last legs. Do I just pull out the lot, feed the soil and allow it to rest, or is there another way?
ASome summer crops continue growing into autumn, providing a valuable harvest. For crops that are on their way out, just remove them, then improve that part of the bed. There’s no need to improve the whole bed at once, but if you’re into the swing of spreading compost, there’s no harm in spreading it as surface mulch beneath plants that are still growing. This means you replenish the whole bed and give it a uniform finish. You can do this at the end of each season.
Importantly, there’s no need to ‘rest’ garden beds. As long as you’re adding compost, it’s growing plants that bring life to soil. Plant roots release sugars, which feed microbes. In turn, microbes break down organic materials into nutrients that plants can absorb. As you need to maintain this valuable relationship between plants and soil, resting the beds has a negative effect.
Continuing to grow plants in the beds means you always have something to harvest, too. To further encourage this amazing, thriving relationship between soil, microbes and plants, minimise tilling by planting directly into the surface compost. See page 63 for a list of vegetables to plant now in your climate zone.