One of Canada’s most famous gardeners once told me that Calgary was the toughest place in which to garden. The usual complaints are the fleeting frost-free season, punishing hails, bone-sucking semi-desert conditions and the diabolical Chinook winds. These are wicked challenges for sure, but I think the most overlooked challenge is the combination of bright sun with too little heat.
Sun but no heat? Sounds like someone’s been in the sun too long. The altitude is the key to understanding this seeming contradiction. During the main part of the day, Calgary is exposed to relentless rays of sun penetrating a thin atmosphere at an altitude of more than 1,000 metres. But the heat fades quickly as the sun sets, as anyone who has lingered in the garden after dusk knows.
The lack of night time heat shuts plant growth down. So, even if we experience a nice long stretch of warm days, our plants shiver through the cool nights, and maybe warm up enough to start growing again in late morning. So, they grow more slowly than in other Canadian cities of similar latitude.
The secret to success with heat-loving plants like tomatoes involves trapping as much daytime heat as possible and harnessing it through the night. One way to do that is to grow tomatoes in large black pots or in special bags designed to trap daytime heat that will keep roots warm all night.
Cut the bottoms off two-litre pop containers and place them over young transplants at night before things cool off to trap cosy warm air around the tender stems and leaves.
Some gardeners cover all their heat-loving veggies in small portable greenhouses. The trick is to keep the sides open during the heat of the day and to close it up at night, thus trapping valuable BTUs inside.
It’s a little trickier to grow some of the flamboyant tropical beauties such as callas and cannas. These bold patio enhancers will accept all the heat you can give them, but even though it rarely gets as hot as it does in tropical places, the intensity of our high altitude sun can scorch their large tender leaves.
As with tomatoes, growing tropicals is more successful in containers than in the ground. And containers situated on warm patios have a further advantage.
I have found moderate success avoiding leaf scorch while still providing heat by slowly introducing plants started indoors to warm shady areas, and eventually bringing them into areas with morning sun and light afternoon shade. But it’s always a race with Jack Frost.
In the garden, place large dark stones around plants that need a boost to cope with cool nights. Dark coloured mulches will absorb more heat than light coloured mulches. But avoid using black plastic over root zones. Plastic does not allow for air or water circulation and heat could build up to killing levels.
If you think of heat as something to conserve, as you do water, your efforts in the short months we have to grow stuff are more likely to be fruitful.
Sidebar: Growing a hot bank account
Horticulturists and farmers use a measure called growing degree days (GDD) or growing degree units (GDU) to measure the accumulated heat over a season. Usually, this is the number of hours in a day that the temperature is over some minimum temperature, below which the plant does not grow. Different plants need different amounts of accumulated heat over the season to grow, flower and set seed. These are known for most plants, and keeping track of growing degree days helps gardeners and farmers predict when bloom or fruit ripening might occur.
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