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Index : Miscellaneous Gardening Topics
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- 40. Find the Warm Spots in Your Yard - Top
If you haven't noticed by now, temperatures in the Winter vary greatly depending on the part of town you live in. Even from spot to spot in your own yard, temperatures can differ by as much as 10 degrees. That can be important when your locating plants in your yard. You may be able to grow quite tender plants in the warm spots, even if you live in a cold part of town.
Warmest locations around the house are those along south-facing walls. Heat from the sun warms these surfaces and the warmth penetrate into stuccoed walls. It penetrates even deeper into masonry walls constructed of adobe, slump and concrete block. During the night, this stored heat is released, keeping plants nearby considerably warmer. This is why bougainvillea planted against south-facing walls are so successful.
Unshaded east and west facing walls can also provide some heat. However, these surfaces are not exposed to as much sunlight in the winter and therefore do not heat to the degree south-facing ones do.
Sunny walls painted dark colors will also absorb and store more heat than light-colored ones. That's great in the winter when the extra heat is welcome, but can be a problem in the Summer. The solution is to plant a deciduous shade tree to block the Summer sun but allow the Winter sun to penetrate after leaves have fallen in Autumn.
Areas in and around the house which have overhead canopies will also be warmer on cold nights. Radiant heat from the sun, stored up during the day in the ground and in paving materials is released at night. This radiant heat is inhibited from escaping into the atmosphere by covers overhead. These might include; patio and carport roofs, house overhangs, large shrubs and shade trees. Bringing tender container plants onto a covered patio can provide several degrees of cold protection. The same can be said for locating plantings under the spreading branches of a tree. Maybe just enough to get those begonias through those frosty nights.
The same radiant heat stored in the ground during the day keeps the area near the ground warmer at night. Low ground-hugging plants can take the greatest advantage of this extra warmth. To be effective, the ground around plants should be cleared of surface coverings such as rock or organic mulch. The sun heats best when the rays come in direct contact with the soil. During the Winter, rake mulch coverings back a few feet from cold-sensitive plants. Moisten the soil by hand watering just prior to a predicted cold snap. Moist soil can absorb a greater amount of heat that can dry soil and will keep the air above warmer.
Knowing where cold pockets exist in your yard can be just as important as knowing where the warm spots are. Cold air is heavier than warm and so it settles in the low pockets and extremities of the yard. It's important not to plant cold-sensitive plants where the cold air will sink and settle. Cold air should be allowed to flow away from your yard and not be trapped by walls or gates. If your back yard is higher than the front yard and is surrounded by a wall, open the gate to allow cold air to flow out. If your back yard is lower than the front, keep the gate closed. This will keep cold air out and force it to flow around and away from your property instead.
Finally, you may want to measure the temperatures in your predicted warm and cold spots. Since you'll need several thermometers, calibrate them before use by placing them in the same location and note any differences in their readings. Keep this information for your records. Because the air is typically coldest about 30 minutes after dawn, use this time to take your temperature readings. Taking into account discrepancies between the individual thermometers, you should be able to get a pretty accurate handle on the relative difference in temperatures between locations. Use this information when planning future locations for cold-sensitive plants.
Written by John Begeman, College of Agriculture and Life Sciences, the University of Arizona, 520-626-5161. - Updated: December 16, 2001
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