Brian Minter: How to get your gardens through the heat

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The extreme heat that we’ve been experiencing over the past week has certainly taken a toll on our gardens — burnt foliage, dried-up annuals and perennials, brown grass, stressed-out containers and hanging baskets, struggling hedges — and the list goes on.

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The key now is to bring those damaged plants and containers back into shape as quickly as possible. There’s a long summer ahead, and we all want to continue enjoying our colour plants, ornamental trees and food gardens.

Baskets and containers, especially those situated in the hot sun, have really taken a beating. The priority now is to pinch or cut back burnt foliage and spent flowers so the plants can regrow. In some cases, it may be necessary to move them to a less-heat-exposed location.

It’s critical not to overwater to the point of the soil continually being too wet. Give them a good drink, then let them become dry. With so much heavy watering over the past week, most the nutrients in the soil will have leached out. Therefore, it’s important to feed your baskets and containers with both a fast-acting, soluble fertilizer, like 20-20-20, as well as a slow-release fertilizer, like 14-14-14, for continuous feeding.

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You should see signs of new growth in about seven to 10 days, and with a little care, things should bounce back.

This weather has taught us a great deal about the tolerance for sun and heat of all our plants. Mophead hydrangeas are, perhaps, the most severely affected. They need moisture deep around their roots to prevent both leaf and blossom burn. In early morning sun, afternoon shade or total shade, they should be fine, but it’s that hot 11 a.m. to 4 p.m. sun that really pushes their risk of burn damage.

Depending on the severity of the burnt foliage and flowers, either pick off the affected leaves and blooms, or in more serious cases, it may be best to prune mophead hydrangeas back and allow new growth to develop. The consequence, however, of pruning most older varieties is that you’ll get no flowers until next year. Newer varieties, like the Everlasting and the Endless Summer series, will rebloom. Be sure to water your hydrangeas thoroughly and deeply.

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Broadleaved plants, like azaleas, rhododendrons and camellias, may also have suffered burnt foliage, especially if they are up against a south or west wall. It is not too late to prune them back. New leaves will come, and, in most cases, there will still be enough time to develop new buds for next year’s bloom. It is also important to rehydrate the roots by soaking the soil thoroughly, especially around the drip lines — outer tips of the branches. Adding a six-to-10 centimetre layer of bark mulch will go a long way in helping to retain more moisture in the soil. Applying a slow-release fertilizer, like 14-14-14, around the drip line will encourage vigorous new growth.

At the end of each summer, many cedar hedges have a number of brown, dying trees. No matter how old our cedar hedges are, they all have very shallow roots. Extended periods of drought or heat can really stress these trees. All hedges need deep watering, and it’s essential to water them as soon as possible. If you use a drip or soaker hose, make sure the water is left on long enough to penetrate deep around the roots. Dig down and check the moisture depth. Once hydrated, they too would benefit from an application of slow-release fertilizer.

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The unfortunate truth is that not all ornamental flowering shrubs and shade trees were planted with proper soil preparation. Far too many are struggling to grow in shallow, poor quality soil. In addition to giving them a deep watering around their drip lines, you should gently work in some nutrient-rich soil to this same area and a layer of mulch would also be helpful. Once again, an application of slow-release fertilizer will boost their recovery.

Most perennials will fare far better than we might expect. In severe hot weather, they may wilt, but with a little mulching and deep watering, they usually bounce back nicely. Some may have finished blooming or simply have burnt foliage, so a hard cutback may be in order. They, too, need a good feeding.

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Many vegetables have already been harvested. Once the extreme heat is over, it will be time to plant late summer and fall vegetables, like squash, parsnips, brussels sprouts and turnips. There is still time to replant cucumbers, tomatoes, peppers and brassicas. Asian vegetables, coriander and spinach will bolt or go to seed in the heat, so hold off planting them until the weather cools. In vegetable gardens, water in the morning if you can and keep water off the foliage by soaking only the root zones to force vegetable roots to grow deeper.

Hot weather will stress virtually all our fruit trees and may cause premature fruit drop. It’s critical that we soak the drip lines around all small fruits and fruit trees to ensure we have a crop to harvest. Applying nutrients around all their drip lines will greatly improve the quality and size of the fruits.

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Roses, too, have blown open rather quickly in the heat. To keep them going, prune back the spent blossoms to allow for new growth and new flowers. Mulching roses with Sea Soil or composted manures and applying some quality rose food is essential right now. A thorough, deep watering is in order too.

We can’t prevent what has just happened in the heat, but we can certainly take steps to fix damaged plants and to do some important preventive maintenance to ensure our gardens continue to supply the beauty and food we so enjoy. Nature can sometimes challenge us. It can also teach us valuable lessons, and we need to learn from them.