Winter is the ideal dream time for cold-climate gardeners, but it’s also a perfect time to review good gardening practices and increase your gardening knowledge. For this Winter Review we’ll examine microclimates.
A microclimate is an area – small or large – that, due to specific topography and conditions, is colder, warmer, moister, or dryer than areas nearby .
A valley is a good example of a microclimate. Because cold air is heavier than warm air, valleys tend to trap cold air, making them prone to early and late frosts. Also, valleys are often moister since they catch downward flowing water. Hilltops, by contrast, often form a very different microclimate, one with drier soils where plantings are more impacted by drying winds.
The temperature of bodies of water, such as a river or lake, will moderate nearby air temperature creating a microclimate that tends to be warmer into autumn or, if the water is ice-covered, cooler into spring than temperatures some distance away from the body of water.
Land slope can also create a microclimate – a south-facing slope will be warmer than a north-facing slope. Vegetation in a flat, open field will be more frost prone than ground level vegetation near large trees since the trees offer some protection from temperature extremes.
Hardscape – pavement, buildings, stone walls – can form warmer microclimates by collecting and holding the sun’s warmth.
Microclimates can create minimal temperature differences – just enough to protect from light frost or entice earlier bloom – or significant temperature differences within short distances. I recently drove through a 10-degree temperature drop in the span of a mile while descending a highway hill into a valley, and watched the car thermometer regain 10 degrees as the car ascended to the next hilltop.
I’ve found hardscape particularly helpful for teasing out an even earlier bloom from late-winter blooming crocus. Those planted near my southwest-facing front steps and walkway have peeked out of chilly soil as early as late January and bloomed in February in my zone 6b garden. Even during very cold years these crocus bloom earlier than crocus planted farther away from the steps.
To improve your gardening successes, familiarize yourself with your gardens’ microclimates.
- Is a moisture-loving perennial struggling under the eave of your house? The house may be blocking rain from the roots, thus creating a dry microclimate. Try giving this perennial supplemental water or consider moving it to a spot that better suits its needs, and replant the area with vegetation that well-tolerates dry soil.
- Have tender vegetables in your garden succumbed to frost when your neighbors vegetables survived? Your garden may be situated in a slight depression that naturally collects cold air or in a slightly more open area with fewer surrounding trees. The simple fix of using floating row covers may be all that’s needed to protect your vegetables from early frosts.
- Is grass simply not growing under a large tree? It’s likely too shady for grass, plus the roots of large trees draw moisture and nutrients from surrounding soil, making it more difficult for adjacent plants to thrive. The microclimate created by the tree is just not conducive to growing grass. Instead, plant a shade-tolerant groundcover that does well in dry soil.
The bed in the photo below was a planting challenge until I was able to observe its seasonal microclimates – how long the sun hit it during spring, summer and autumn, how it drained, and when the soil warmed each spring.
The bed is part of a northeast-facing retaining wall between an upper lawn and the lower swimming pool. It receives only early morning sun until late spring, becomes downright toasty when mid-summer sun is high, and remains warmer than nearby beds into mid-autumn. You can see it is totally surrounded by hardscape. The soil, which rests atop landscape fabric that covers crushed stone, is about a foot deep. Because the landscape fabric holds moisture, the soil remains moist except in very dry periods and becomes downright soggy during periods of ample rain.
It took a few years of trial and error to figure out how to best utilize this bed. My original plan of inter-planting it with flowering annuals and edibles only works when I sink clay pots into the bed to hold plants that don’t like wet feet – the added height of the clay pots and the moisture-wicking action of the clay helps keep the potted soil from remaining too moist. I plant mostly moisture-loving annuals directly in the bed’s moisture-holding soil. And I rarely need to water the bed except during very dry periods.
The warmer microclimate created by the adjacent hardscape makes this bed perfect for growing hot peppers, provided they are planted in the clay pots where their roots don’t remain too moist. This microclimate is ideal for tender, warmth-loving annuals like coleus that thrive on the steady moisture of the bed’s soil.
Before studying the microclimates created by the various conditions in and around this bed I had many plant failures – early-sown, direct-seeded lettuce grew poorly in too-wet soil and early transplants suffered from too-chilly soil.
By recognizing the unique microclimate of this bed, I was able to turn a challenging planting area into a productive place for warm-season annuals.
If there is a challenging planting area in your landscape, try studying its microclimate. You’re likely to learn how to turn a challenge into a success as well.