Season Extension (SE) is a collection of techniques enabling fruit and vegetable growers manipulate growing conditions for harvesting a longer period, and includes tools and activities from simple frost cloth over tender plants to high tunnel structures that resemble traditional greenhouses at first glance (and much between).
For home gardeners who want to continue growing vegetables as late as possible in the season, season extension is an indispensable tool. Local vegetable producers rely heavily on SE, using high tunnels and row covers on a regular basis. From responses to the February column “Five ways to get a jump on spring planting” in this space and social media discussions about the article, it’s clear that SE is not widely used among home gardeners. SE is for serious gardeners seeking to maximize food production. SE also helps protect investments of tender ornamental plants, reducing chances of plants ruined by “unexpected” cold snaps and “freak” snow events — like that hard frost that happens every second week of June.
The “grandfather” of SE is farmer/author Elliot Coleman, whose books “The Four Season Harvest” and “The Winter Harvest Handbook” revolutionized SE for small-scale produce farmers, with many techniques easily modified to the home garden. Coleman’s work comes from farming in Maine, so the general concepts and some techniques remain true in the Klamath Basin, but the details and execution will be considerably different. Check out Coleman’s books, or the web resources listed in the sidebar, to further explore these concepts of SE.
Thermodynamics: It is common for gardeners to overlook the soil as a heat reservoir. Soils vary in heat retention properties: sandy light soils warm up earlier in spring, while wet soils conduct heat better than dry soils. Raised beds warm up earlier in spring, but may become too warm, or dry too quickly in summer. Trapping ground heat near plants using covers, is an example of using thermodynamics use existing heat to keep plants closer to ideal growing conditions. Other types of heat management might include crop positioning on a slope, how and when crops are watered, and using windbreaks.
Mulches: Most gardeners value of mulch for weed suppression and water retention. We can expand the concept further by understanding properties of various mulches, even using different mulches in different seasons. Black plastic mulch, a staple of commercial vegetable production, conserves moisture, blocks weeds, speeds up production and warms soils. Black plastic mulch keeps soil warm through soil contact. The better the plastic/soil contact, the better heat conductivity. Other mulch colors can reflect light, slightly reducing soil temps. Research showed red mulch may increase tomato production and reduce early blight compared to black mulch (Penn State University). Where growing conditions are ideal the red mulch showed little benefit — but growing conditions in the Klamath Basin are not ideal. Red mulch may be worth trying on eggplant, melons and strawberries.
Row covers: Fabrics vary from thrift-store curtains and sheets to “frost cloth” found at garden centers and designed especially for the purpose. These require the labor of application and removal, but trap heat near the plants when it is most needed at night and early morning.
Structures: There are numerous types of high tunnels. Most look like a traditional greenhouse from the outside, but use only passive tools like ground covers and heat capture, rather than burning wood or fuel. Most “greenhouses” for home growers are really high tunnels as they don’t include heating systems. High tunnels create an environment for crops that is considerably warmer than outdoors. This is great at night, but often requires opening and closing of vents or doors during the day to keep plants from cooking: Automated options for venting are worth considering. Reducing the spread between daily high and low temps is a primary goal of many season extension techniques. A difference of 40F or more between the high and low temp is stressful on plants and causes production issues.
Throwing shade: While many SE techniques are designed to make the crop environment warmer, there are also reasons to consider shade in the SE lineup. Lettuce, spinach, carrots, cabbage and its relatives all prefer temps in the 70s and 80s for best performance. Big shifts between day and night temps cause these plants to bolt, or flower prematurely, reducing yield and negatively impacting flavor. Planting these crops under shade increases summer production success by reducing this spread.
To be clear, none of these techniques alone is going to provide a year-round growing environment for vegetables in the Klamath Basin. Cold temperatures aside, There is not enough sunlight during the winter months for good plant development. However, the use of SE can turn our questionable 90 to 100 day growing season to closer to 120-150 days — enough to greatly increase production without spending every summer moment in the garden.
Nicole Sanchez is horticulture faculty at OSU’s Klamath Basin Research and Extension Center. For more information on this or other gardening topics, contact Nicole at Nicole.email@example.com or 541-883-7131.