Water truly is the essence of life, all the more so in our continuing drought. Unable to move to water, trees are totally reliant on rain and snowfall and what you apply. Trees have a yearly routine that includes several important watering times. Trees lose water from their systems all winter. This is especially severe in Calgary in the heart of Chinook country. With the regular movement of water through the soil nearly shut down due to ground frost, a tree's ability to take up and replenish lost water is marginal at best.
As soon as the frost is out of the ground, a watering of a minimum of one inch, preferrably two, should be applied under the tree's entire drip zone. The best way to measure your water application is by placing one or more measuring cups in the area you are watering. Then you can gauge the time it takes with the watering equipment you are using to apply the two inches you want.
This first watering should usually occur by mid- to end of April. Calgary's climate is always variable. From spring to the end of June is normally our monsoon season. Typically, if we are going to get much rain, it will come during this time. Again, a water or rain gauge is a good idea, so you know what you have got.
By July, when the heat hits, all trees will need approximately two inches of water every ten to fourteen days to stay healthy. Some trees (birch, for example) will need that much each week. If the heat really picks up into the high 20s or 30s Celsius, you may want to increase your application by as much as an inch each time.
Any time during the summer when heavy thunder showers and hail occur, measure these free natural waters and possibly skip your next watering. Water falling on roofs and directed away from houses through eaves and downspouts should be taken advantage of. Next time your eaves need replacing, make sure that they are set up to maximize the use this free water and deliver it to your trees. Or do it now; downspouts that drain water into alleys or storm drains are a serious waste.
As fall approaches, if you use this watering plan, your trees will have had a great year and should be looking their best, with good colour, thick luxuriant growth, and little internal dead wood. Continue watering until the first week in October. At this time, do a heavy “get set up for winter” watering. Double your usual application, then leave them alone. During this time, the trees will be “adjusting their anti-freeze” or going through their fall changes that will prepare them for dormancy in winter. What must not happen is to water your trees in mid- to late October, have them take up this recent application, and then be hit with a deep cold spell right after. This effect can cause a lot of tissue damage and die-back.
If you have personalized your own water program to fit with the trees in your garden and followed it, you have done everything you can to ensure your trees' health. There is no need to water during the winter. The ground is frozen and this water will usually just freeze on the surface and not be available to the roots. By waiting until the frost is out in the spring and then starting your watering, you won't fool your trees into thinking spring has come and starting their early growth before risk of freezing weather is past.
The best way to water trees is a heavy, long-duration single soaking during your one to two week watering period. The reasons for this are twofold. One, grass is a serious competitor for your tree's water; once the grass and its roots are wet, then the tree's roots and soil below the grass can get some water. Two, several brief waterings through the same one to two week period will keep the lawn looking good, but will supply little extra for the trees. Most home irrigation systems are set up this way. Your trees are relying on you to get moisture into your black soil zone and have a reserve there that they can draw on as they need it during the one-to-two-week watering period.
The amount of loam under your grass and tree roots has a huge impact on your ability to store water and how you will work your watering system. The thinner the loam layer under your grass, the smaller your water reservoir. Some lawns are installed on only six inches of loam. Dig and explore; know how much black soil you have. If it is thin, you will have to water more often due to having a smaller holding tank.
The best times to water are whenever you have time to do it. It is much more important that the garden and trees get their water rather than not. During really hot weather, you will lose less water through evaporation if you water early in the morning or late at night.
As dry as Calgary's climate and clay-based soils can be, a few cautionary notes are in order. Don't overdo it. It is possible to drown trees. Be careful of permanently wet spots, low areas and the path of water flows from your downspouts. Mosses, horsetails and even cattails are all positive tell-tale signs of permanent water. If you want to know for sure, always check the soil by digging. As you try your watering program, check the results at four, seven, ten and fourteen days later. Take note of soil texture and clumpability and overall moisture content. Your hand is the best gauge there is. Once you have watered and tested, you will have learned a significant amount about how water moves through your garden. Like all seemingly simple things, this is not so simple. It changes for every garden, every different combination of plants, trees, soils, drainages, etc.