Extending the Growing Season

This year most of Alberta has had a longer period without frost, and many areas have been lucky enough not to be hit yet, and it’s nearly October! Well if you are looking for ways to dodge the first few days of frost when they do happen, here are some options-both obvious and maybe not so obvious (and if your garden has been hit, start planning for next year).

Frost generally occurs for two reasons:  
1. Either there has not been enough heat accumulated throughout the day or 
2. The heat that was accumulated has been allowed to escape to the point the temperature drops to freezing.

Drop Cloth—for a simple “Band-Aid” solution, the old standby, quick-fix is the drop cloth. Use any old bed sheets or blankets and make sure not to break any fragile branches. Placing stakes into the ground every few feet is a good way to keep the branches safe. This can work for fruit trees as well, depending on size. Remember to remove each morning after frost danger has passed.

Mulch –Although not really a viable solution for protecting tomatoes or other large annuals, mulch is an option that prevents the escape of heat into the atmosphere and would generally be used on plants less than six inches in height, or to protect roots of perennials over the winter. In addition to preventing water loss, it acts as an insulator. Good mulches for autumn include leaves and other organic debris.

Water—Water acts as a temperature pacifier and keeps the ambient temperature from fluctuating as much as it otherwise would in drier conditions. The key here is to ensure the temperatures at the time of spraying are not already close to freezing. Watering near or just before the warmest part of the day is best as long as most of the water does not evaporate before nightfall. Another idea is to use water that sits in a rain harvesting system that has been sitting in sun for several hours. Just be sure not to shock the plants by any sudden temperature changes when first spraying.

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The following may be too late to start implementing this year, but these are some you may contemplate for future seasons…

Heat sinks—A heat sink is any physical body that collects the sun’s radiation throughout the day and releases this captured heat after dark. Such examples include large rock or brick masses, water tanks, and anything especially dark in colour. Remember that the effect can vary greatly depending on the type of material used as well as its colour. Experiment and do your own research.

Elevation—the areas especially prone to frost depend on elevation. So which is it, the higher areas or the lower areas? Well, both actually. Cold air tends to sink to the ground and ‘pool’ at the lowest spots as if it were water. At the same time, areas on the peaks of hills are more exposed and the soonest to fall victim to cold air masses. So the best answer is whenever possible, plant the most tender plants in the mid-elevations. They will be protected by the higher surfaces and most of the coldest air will sink to the lowest spots first.

Planting under a frost barrier—Finally, planting larger and less frost-sensitive plants and trees in such a way as they shield the lower plants from heat loss is an excellent way to keep the ground temperature from dropping to freezing. The general rule that works best here is, the less of the night sky that is visible, the less heat will be lost. Conifers or any tree with broad, over-hanging branches are good options. Just ensure that they will not shade out the plants, so planting these taller trees on the north side of fragile lower plants is a good solution. 


Finally, many root vegetables such as carrots, parsnips, turnips and so on can be kept in the ground for several frosts. Some say it actually enhances flavour. For extra protection, simply cover in a six-inch layer of mulch and in Calgary's climate, this should suffice for well into October.

Remember that it only takes a couple of hours for frost to cause damage. iin most cases the best we can expect is about a few degrees maximum that we can affect the temperature. This is done by collecting the sun’s energy during the day and making sure it stays with the most sensitive plants at night. Sometimes though this can make a huge difference when the autumn sees just a hand-full of days that hover around freezing, followed by a couple of weeks of warmer nighttime temperatures. So take advantage of the longer growing season with these few simple measures against frost.

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