Season Extension Applications for Spring

When gardeners discuss season extension, they commonly relate it to gardening in Autumn. Leaves are falling, the soil is still warm, and temperatures are steadily dropping—season extension in the fall entails creating supportive structures that help protect plants from the elements. Did you know, however, that this practice can be “extended” to the other side of the growing season as well?

While fall season extension focuses on preserving plants, spring season extension is about giving your vegetable garden a head start. Employing many of the same methods utilized in the fall, plants can become established sooner, enabling earlier harvests and more opportunities for planting succession. This, in turn, becomes particularly useful when late spring frosts and even snow arrive, threatening young plants.

That is not to say, however, that spring season extension does not come without its own unique challenges. Unlike the steady cooling of fall, spring often brings rapid temperature fluctuations. Under a protective structure, hot temperatures can result in steamed, scorched, or even cooked plants if not carefully monitored. Additionally, unlike in the fall, no residual heat is left in the soil, which can delay germination even if ambient outdoor temperatures are adequate. And then there is the matter of just how cold protective structures can get.

So, what are these structures? Season extension supports range from low tunnels, cold frames, and row covers to simpler solutions such as mulches, soil covers, or makeshift “cloches” from upturned bowls, buckets, and milk jugs. The primary objective of most of these is to create a microclimate that preserves ambient air, shielding plants from wind chills and harnessing the greenhouse effect for warmth. One critical caveat: plants can’t touch the edges of their coverings, as direct contact will result in freezing at those points.

With these supports, seeds can be sown safely when soil temperatures have reached a minimum of 40-50°F, depending on the specific types of spring crops being grown. Spinach, lettuce, and radishes can tolerate the colder end of the spectrum, while peas and carrots prefer the middle range, and beets and turnips thrive at the higher end.

Ensuring seedling success will also require maintaining adequate soil moisture. The good news is that many support structure methods mentioned help minimize evaporation. As a result, additional watering is often not necessary during the early stages of establishment.

When monitoring ambient temperature fluctuations, bear in mind that excessive heat damage generally occurs when the internal temperature within a cover reaches around 75°F. In such cases, removing the cover or providing ventilation may be necessary to allow cooler air in, while warmer temperatures persist. On the flip side, when internal temperatures drop below 28°F, even coverings may fail to prevent plant damage.

Spring season extension can be a valuable tool for your upcoming vegetable garden. Just remember to monitor those temperature fluctuations, pay attention to the internal environment of protective structures, and be ready to adjust as needed. With these precautions, you’ll be set for an even more bountiful growing season.

by Anthony Reardon, Horticulture, Small Farms, 2024