I’ve been thinking about the issue of microclimates quite a bit lately, as we are planning a new kitchen garden. One of the things I would like to accomplish is to get my Meyer Lemon tree out of its pot and into the ground. Since we live in zone 7 and have been treated to temperatures as low as 16 degrees F, I will need a microclimate to prevent the poor thing from freezing its tootsies, leaves and everything else. Meyers generally do better in zones 8 or 9.
Microclimates are areas within a larger climate zone that are warmer or cooler than the surrounding territory. They can be as small as a few square feet or as large as many square miles. In the right microclimate, you could be as much as three climate zones warmer or colder. Warm microclimates seem to be what most folks look for, in order to grow something that just can’t make it in the primary zone’s winters. But sometimes, you want a cooler microclimate — say an area of the garden that gets summer shade during the afternoon where you can plant heat-sensitive lettuces.
Lots of things affect microclimates: soil, wind, sun, water, rocks and shade. Since we have a heavy clay soil in the new garden spot, I need to add compost to increase water drainage; wet soil tends to stay cool and can freeze more easily. On the other hand, clay soil can act like pavement and radiate heat at night. Our big pond creates a microclimate because water absorbs and releases heat at a different rate than the surrounding soil. Low ground tends to be colder than high ground because the cold air settles. A high, bare ridge, on the other hand, tends to be both hotter and colder than the slope below it. A south-facing slope (assuming you’re in the Northern Hemisphere) gets more sunlight. Buildings, rocks and pavement absorb heat during the day and radiate it back at night.
The new garden spot is a south-facing slope (close to the house, as a kitchen garden should be). There are several largish rocks that will need to come out, so my plan is to set them up above ground to the north, east and south of the site where I want to plant the Meyer Lemon. A half circle of big rocks will act as a heat collector all year round, releasing stored heat near the lemon at night and in the winter when it’s cold. I may also use rock mulch under the tree. I may still need to provide some protection on really cold nights, but that’s easily done. Small Christmas tree lights work well, and since they’re only needed when the temperatures are heading to 25 or below, I don’t need to use them very often; minimal electrical cost. I’ve even used an old comforter to good effect on chilly but not really cold nights.
Here’s hoping life hands me lots of lemons!