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Growing Hydrangeas, Camellias, Magnolias, Rhododendrons and other cool climate plants in hot weather

I have always been a cool climate gardener, which might seem odd seeing as the Adelaide foot hills, where I live, are known for their soaring summer temperatures. While they don't get as hot as the city or the plains (Adelaide is a very flat city, as is much of Australia) they do still experience temperatures in excess of 40 degrees celsius. When I say I am a cool climate gardener, that means that my garden's plants are sourced from areas of the world which experience mild summers and cold, sometimes snowy winters. Most of the plants I love are from the mountainous regions of China and Japan. While Adelaide winters are generally quite cold and adequately wet, I am not alone in my defying of South Australia's dry summers. Hydrangeas, Magnolias and Camellias are always popular sellers at nurseries around the area and throughout most of the world. These plants are so amazingly alluring that they tend to attract attention from even the most inexperienced of gardeners. Though the same is true of more weary plant keepers being scared off by the perceived fragility and soil requirements of many cold climate plants.

Hydrangea Macrophylla in my garden

I am asked quite regularly how I keep my garden flourishing throughout heat waves and extended dry spells, and the short answer is: diligence. Keeping plants happy in locations where they wouldn't naturally be means work for their care taker. That isn't to say these plants lack hardiness though, it's just that they're hardy to temperature and weather conditions Adelaide never experiences. Most plants don't mind ambient heat too much. As long as they are sheltered and their soil is moist they can tolerate almost any air temperature. In fact, hot weather is never really a problem for plants, they suffer most from the conditions which heat brings with it: sun and dryness. Without a doubt the biggest killer of plants in warm climates is dryness, nothing will kill a cool climate plant like lack of water. Hydrangeas are the most susceptible to this lack of water. Most hydrangeas, especially the popular and well known Hydrangea Macrophylla or 'Big Leaf Hydrangea' have very broad leaves with little flesh thickness. This means that hydrangeas perspire at a much faster rate than many other plants, meaning they are thirsty for extra water more frequently. I sometimes refer to my hydrangeas as "the plants of paradox" because they love moisture, but hate soils that stay wet. Similarly, hydrangeas love the sun, but hate its heat. The key to happy hydrangeas, and indeed happy camellias, rhododendrons, and most magnolias, is purely situational. These plants require very minimal care if they are planned for and given a spot that meets their conditional requirements. Pots are in my opinion the best way to grow hydrangeas in hot climates. The benefits of which are numerous, first and most simply: pots are mobile, if you chose a position that is too sunny, your hydrangea will wilt and yellow, if the position is too shady, your hydrangea will reward you with a flush of weak leaves and no flowers. Place your potted hydrangeas in a spot which faces east and gets the first 3-4 hours of the morning's sunshine, though a position in a spot which gets the last hour of the afternoon sun can work too. None of that means much though, if you aren't going to commit to watering them every second day throughout the summer. The best spot for a hydrangea, camellia or rhododendron is somewhere it can't be overlooked. Somewhere easily accessible with a hose or watering can. Another benefit to keeping these plants in pots is that ample water is easier to monitor and drainage seldom becomes an issue, You should feel guilty ignoring these plants on a forty five degree day when you're sitting inside your air conditioned living room. You bought these plants and took their lives into your hands, now it's your job to keep them alive! That all got a bit morbid, didn't it... Look, keeping these plants, most of which are shrubs with woody stems, isn't hard, it's just not as easy as say, having a cactus garden or sticking purely to native plants. My three big tips for these cool climate plants are as follows:


Use premium, purpose made soil compositions for pots. This means acidic potting mixes, for most cool climate plants, the most expensive you can justify. Not only will they hold water better than cop-out non Australian-Standard mixes, but you will see the extra money transform into lusher foliage and brighter blooms. When you put a plant in a pot, you have unbridled control over its health. You choose the soils and fertilisers it is exposed to, the water it gets and the way that water drains. As most gardeners know, the colour of hydrangea flowers are dictated by their soil PH, alkalinity makes them pink and acidity turns them blue. I plant my plants in the ground too, but this is a less economic option, plants need more water to stay healthy in summer and in my case, large excavations were needed to clear deficient soils and make room for rich loam to be brought in.


Just because they're in the shade doesn't mean they don't need as much water. Just as turning up your oven's temperature doesn't cook food twice as fast, keeping plants in dense shade areas doesn't equate to less water needed. Dry shade is the enemy of most plants, in fact, Clivias are everywhere in Adelaide because they're one of the few plants that will tolerate the dry conditions under large trees in the droughts of late summer. Always pick a sunnier spot next to the tap over a shadier one at the back of the garden. Human beings are almost unbelievably lazy, and there's no point telling yourself you're different because sooner or later, a plant which is out of sight gets ignored. Leave those spots in the garden for hardier perennials.


Don't use saucers. There seems to be a real dislike for the use of saucers beneath pot plants these days. People think that residual water around a plants roots will make them rot, but this isn't always true. I have a large collection of ferns in pots. I have tree ferns and a lot of nephrolepis growing in the ground throughout the garden but the rest of my ferns sit close by the house or in my greenhouse in terracotta pots with saucers beneath them. Never have I experienced root rot in any of these potted ferns, I even have some Japanese Anemones in pots with saucers that have thrived for years. However, as I have mentioned above, hydrangeas, camellias, magnolias, rhododendrons and indeed most larger shrubs do not appreciate saucers beneath them. All these plants love and need free draining soil, and saucers obviously inhibit drainage. While this does mean they dry out quicker, I have found that it is not worth corner cutting with saucers or drainage hole inhibitors.

I hope I have been of assistance to those entering the wonderful world of acid loving cool climate plants, there is a lot more to know but I feel with this basic knowledge, anyone can start a successful relationship with Hydrangeas, Camellias, Magnolias, Rhododendrons and Azaleas. Feel free to ask me for more information.

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