Putting the right plants in the right places can make the difference between thriving and barely surviving. The secret is knowing your yard’s unique microclimates.
According to an old song, the devil made Texas. But the sand was too hot, dry and poor — even for hell — and he had to make use of bogholes, brambles and rocks to make the place really work.
Therein lies a reference to one of the most basic rules of Texas landscaping, whether you’re trying to grow scorpions or vegetables: learn to recognize available microclimates and use them to their advantage.
A microclimate is a set of local atmospheric conditions that persist over time, setting it apart from the surrounding area. Put a pretty potted flower out front for two weeks in summer, un-watered and you’ll see the point. If it’s in the shade, it’ll likely be alive at the end; in full sun and it’ll likely be fried.
Microclimates were first described in the 1950s, but even in San Antonio a few common sense building strategies had already taken them into account: southeast-facing windows and sleeping porches to capture gulf breezes at night, large rooftop overhangs to minimize heat gain, and of course summer homes in Fredericksburg.
The most impactful example today may be the “urban heat island” that can be regularly viewed on the evening weather. Thanks to urban asphalt, concrete and tar, the entire metropolitan area tends to absorb and radiate summer heat, dissipating approaching rainstorms like Moses parting the Red Sea.
In the home landscape, microclimates can be any combination of site-specific factors that either relieve or amplify plant stress. For example, cold air and winter humidity both tend to flow downward, pooling at lower elevations on flat areas; frost forms on lawns and car windows even when the ambient temperature is higher.
USDA Plant Hardiness Zones cannot take your local conditions into account, but if you can learn to identify where microclimates occur, you can use them to select, position and care for plants — and in many cases save a lot of work and water.
Here’s a few things to look for in south central Texas.
North or South
Any house, wall, fence or building can be used to illustrate the effects of wind and sun. A south-facing wall that absorbs heat on a winter day will also radiate it back to surrounding plants at night, like the classic Mexican olive at the Alamo. By the same token, many delicate tropical plants and fruits may be protected from winter winds by placing them in the lee of the stone.
Similarly, trees growing on the south face of a big slope will be exposed year-round to more sun- and heat-stress than on the north side. This can be seen in Hill Country canyons as much as in San Antonio street plantings: in a recent landscape job near San Antonio College, all the south-facing red oaks at a new apartment building died; those protected, on the north side of the same building, were fine.
Morning or Afternoon
You’ll often see references to “morning sun” on plant tags and gardening pages. Just as locations on varying slopes can make a long-term difference in the forest composition, morning sun implies afternoon shade, and this can become critical in preventing heat exhaustion on individual plants during extended summer scorch.
Sun or Shade
For plants in Texas, the difference between shade and sun is the difference between the good life and being torched. For example, “inferno strip” refers to the strip of land between the sidewalk and the street, and depending on tree cover, plants there may be exposed to drying and winter wind, sun and radiant heat from both asphalt and concrete. Often this is the spot where turf won’t cut it, and you’ll want to use the hardiest plants available.
In contrast, life is cozier in the landscape beds, and even in winter, just a few overhanging branches can be enough to protect tender vegetation from tissue damage. Unlike the inferno strip, a full grown landscape will have many layers of leaves and protection at different heights and directions.
Most importantly, shade can often be traded for water. Irrigators will often point out that water requirements are much lower for plants in shade — often half as much.
As a rule of thumb, when planting a new landscape many gardeners are tempted to start off with favorite plants from distant hardiness zones. Do not let preconceptions tempt you. Use the old garden adage, “the right plant for the right place.”