A Microclimate Experiment

Microclimates can be a farmer’s or gardener’s best friend. A few years ago, I wrote about how use of microclimates, or pockets of a garden that have varying temperatures and exposures to weather elements, can expand your choice of xeric plants.

cactus greenhouse atlanta
This greenhouse in an Atlanta-area garden provides extra heat and sun for the homeowner’s succulent collection and keeps rain off the plants!

The easiest example of a microclimate is a greenhouse. Windows let sun in and walls, a roof and other strategies help maintain the warmth. Add a heating source (and enough space) and you can grow nearly any plant any time of year.

lava rocks microclimate
The Desert Garden at the Huntington in San Marino, California, is a perfect microclimate for cacti. Not so perfect for humans on the day we visited. The lava rocks intensified the 100-plus temperatures.

Subtle microclimates exist all around your yard and gardens. Structures and hardscaping absorb heat during warm hours and release it gradually, helping to protect plants from cold; they also can protect plants from wind. Partial shade shields plants from heat, and slopes or other topography alter how the overall climate affects a given plant.

pond water lilies
Not far from the Huntington, a homeowner’s pond was filled with blooming water lilies in basically the same climate.

The Zinnia Experiment

I would like to say that we planted zinnia seeds in three different places simply to later show how microclimates affected their growth and hardiness. But I’d be pushing the truth. I did plant them in several different spots to see how well they grow here and how quickly they bloom, so I can use them as an easy annual filler to add color and even more pollinators to our gardens.

So, we put seeds in open space in our vegetable farm rows, mostly for the pollinators. We also planted some on a fairly exposed raised bed in our xeric garden. Finally, we planted seeds in the lower part of the xeric garden, close to the rock wall. All of the flowers did fairly well, although the ones in the farm area had better soil and more consistent drip watering. They were the tallest and healthiest. The ones in the raised bed took longer to come up, likely because of poorer soil and an inconvenient hand-watering location. The flowers planted in the lower bed did almost as well as the ones in the farm area.

zinnia cold damage
The healthiest zinnias froze the most, likely because of the farm area location and the fact we had pulled up several rows of faded vegetable plants, so these zinnias were open to a pocket of frost.

Then the frost came and the healthiest plants burned the worst. They more or less bit it overnight.

The zinnias in the raised bed were nearly as bad, but at least the flowers kept their color (I planned to take photos of them, but hard-working hubby cleaned up the bed before I had a chance.)

zinnias minor frost damage
These zinnias suffered some frost damage, but the flowers were still vibrant, thanks to their protected location near the rock wall.

The zinnias in the lower bed fared the best. I doubt they will grow or flower more, but they don’t look like they belong in a horror movie.

How to Use Microclimates

The experiment helped me get a sense of microclimates on our land. We’ve always assumed that our farming area is cooler because it is in a sort of mini-valley jut above the river. The dead zinnias demonstrated we were right, especially since those plants were the most robust before the freeze hit. The flowers in the raised bed are more open to cool air; there were no other plants nearby or much hardscape to absorb heat either.

The hardiness of the zinnias in a more protected and “solarized” spot near the rocks was telling. It’s always important to think about sun and shade exposure, but sometimes we fail to consider how placing a few large rocks behind a cold-sensitive plant can help it survive winter. In vegetable gardening, for example, using fabric to cover plants creates a micro-greenhouse effect. And when growing a plant that needs a little less sun or heat, shade cloth or plant placement can lengthen growing seasons.

shade for vegetable plants
Peppers love heat, but these pepper plants in Tucson had shade over them for protection.

Microclimates, like the general climate, can vary. For example, a tree that drops its leaves provides no shade until it fills in late spring. As trees mature, they can begin shading a plant that once received full sun; it might be time to transplant a shaded shrub. Windbreaks help slow the flow of cold air streaming up a slope.

rio Ruidoso bench
Every gardener needs a microclimate too! we placed this bench in a shaded area near the river as a spot to cool off on warm days working outside.

Containers offer excellent microclimates, not only because they warm up quickly, but because you can move them to solve sun and wind exposure issues, and all the way inside before the first frost.

adenium in container
This Desert Rose (Adenium) in Tucson is about 10 times the size of ours. But its location in a container means that botanical garden staff can move it if necessary for changing seasons and microclimates.