Small farm microclimates

How to use shade & shade cloth to create small farm growing zones.

Experienced farmers will often tell you how the sun passes over the farm at different times of the year, even if they aren’t talking in terms of north, east, south, and west. They may point to the path across the sky, describing the pattern. And as the sun sinks in the sky during the short winter days, they’ll tell you about how that group of tall trees next to the garden casts a long shadow over a full quarter of the garden area although it still protects it nicely from strong winds. Nearly every farm has microclimates of one sort or another.

The term "microclimates" refers to close proximity areas that vary in climate conditions. In a simple example, trees can affect exposure of the amount of light and wind a certain area of the farm receives. These variances are important to consider when deciding what to plant, when and where, impacting both growth and yield.

Factors of Microclimates

From a macro perspective, microclimates are often noted when looking at urban and rural settings. In the urban setting, things like the asphalt, concrete and buildings absorb the energy of the sun, heating up and then releasing that heat back into the air. This results in higher urban temperatures than in rural settings. In the rural settings, factors like proximity to water may cool down the air, resulting in more moderate climates at times, advantageous to areas with high summer temperatures. Water bodies like lakes, ponds, reservoirs and streams not only affect temperature levels but also humidity levels (more water in the air).

The soil itself can cause climatic variances, mostly due to the amount of moisture absorbed and then evaporated back into the air. Clay soils retain more moisture than sandy soils and can affect the humidity and air temperatures of an area. Knowing the composition of your soil (sand, silt and clay) will provide a baseline for the effect it can have.

The slope of the land is another factor that can affect climates, with some areas receiving more sun radiation than others. As the days get shorter and the sun sits lower in the sky, shadows can lengthen and block out entire portions of beds. Therefore, it’s a good idea to place garden structures further apart in the garden during these times to allow for more direct sun exposure. Sometimes, the wind can whip up and around slopes, damaging plants. Areas like this should be treated as any high wind area, and setting up wind blocks, either naturally or synthetically, can help protect plants and infrastructure. Even though strong winds may not directly kill plants, they can stunt the growth or set the plant back.

Microclimates can be effectively used in farming practices too. For example, in market farming (using a small amount of space intensely), plants are spaced with precision so that they quickly reach a point where the leafs touch, creating a canopy and shading out the soil underneath, mitigating potential weed growth and protecting the soil. In this situation, the farmer is intentionally creating a natural microclimate within a single bed.

Intentionally Creating Microclimates using Shade Cloths

The use of shade covers is an effective way for farmers to intentionally create artificial microclimates by blocking out a portion of the direct light, reducing the average temperature around your plants by 10 degrees or more depending on the density of the shade.

Shade cloth consists of either knitted or woven fabric made from polyethylene or polypropylene and naturally resists mildew and rot. Knitted polyethylene shade cloth is the most common variety used for covering agricultural structures because is has some give (will stretch a few degrees), is lightweight compared to woven fabrics and doesn’t fray along the edges. It is very durable and can be easily and quickly installed, especially when used in conjunction with cover hold-down clips, which firmly grabs the cover, holding it in place.

Which Shade Cloth is Right for You?

There are a variety of different shade cloths to choose from and the use for them will depend on farm location and direct sun exposure, so knowing the uses for the various different available options is advantageous to maximising production wherever you are. They are offered in percentages of light blocked. For instance, 30% shade cloth would allow for 70% light transmission.

The most commonly used shade cloth percentages for protecting vegetable crops range from 30-50%. In cooler climates, 30% shade cloth is the recommended density for extending the season into the summer for cool-loving crops like lettuce, spinach and cole crops, whereas in warmer climates, 50% shade cloth is recommended for these same crops. In both cool and warm climates the use of 30% shade cloth is being used effectively to protect Solanaceae crops like tomatoes and peppers from sunscald.   
Paying Attention to Plant Growth

It is important to pay close attention to the plants as they grow under shade cloth due to the fact that if they aren’t receiving enough light, they may become leggy, stretching and stressing for ample light. One grower we’ve talked to recently had experienced this while growing salad greens under shade cloth during the heat of the summer. What they quickly learned was that when they kept the shade cloth on an entire day, the greens became leggy and droopy, but if they gave the greens full light until 3-4pm, only putting on the shade cover after misting off the greens, they did just fine.