Understanding Garden Microclimates

Home Grown  by Keith Reed
In garden and landscape terms, microclimate is defined as a unique area within the landscape that provides a growing environment different than the larger surrounding area. This can be due to a change in temperature, moisture, wind or any combination of the three. While microclimates can happen in nature, in most landscape situations they are artificially created because of the built environment; be it a building, fence, pond or other landscape feature.

Payne County is in USDA Plant Hardiness Zone 7a. This suggests our coldest winter temperatures will typically fall into the zero to five-degree range. Microclimates can work to a gardener’s advantage in many ways but creating a buffer from this cold is perhaps the most common. For example, we may be able to grow plants that are normally only hardy to zone 8, (or in some cases, even zone 9) by planting on the southside of a brick or stone house that also features some provision for blocking the wind.

It should be noted that microclimates can also work against a plant in a landscape situation in surprising ways, so it is good to know a little bit about a particular plant and its characteristics. Good examples would be early flowering trees like apricot or saucer magnolia. While neither of these trees has a problem with winter hardiness, they are both very early bloomers. Planting in a warm microclimate will cause them to flower even earlier, setting them up for near certain frost damage and the loss of flowers and/or fruit.

These two species will do better in areas on the north side of a building or an open area with a northern slope. This will be the last area for the soil to warm, which delays green-up and flowering. While this does not guarantee the tree will be spared from frost or late freeze damage, it does improve its chances by limiting bloom exposure to possible frost events.

When considering wind effects on microclimate, two issues come into play. One is the direct influence of the wind, which can cause leaf tattering and additional water use. Another is the increase in humidity when air is trapped, or not able to circulate freely. A rose is a good example of a plant that can be impacted in this case. While protection from the wind can help the blooms last longer, an increase in humidity brought about with total wind blockage might lead to an unwanted increase in humidity, creating an environment with a high potential for disease development.

Hopefully, these examples will help you to consider the importance of microclimates when it comes to plant selection and maintenance in the landscape.

For more information on this or any other horticultural topic, you can contact Keith Reed, the Horticulturist in the Payne County Extension office. Keith can be reached via email at keith.reed@okstate.edu, phone at 405-747-8320, or in person at the Payne County Extension office, located at 315 W. 6th in Stillwater.

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