In agriculture, season extension refers to anything that allows a crop to be cultivated beyond its normal outdoor growing season.
For colder climates, the fully heated and artificially lit greenhouse is the ultimate season extension device, allowing some crops to be grown year-round, through sub-zero winters. An energy-expensive approach. There are many other ways to beat the cold, for earlier spring planting and growing into the fall and winter:
- Row covers: Light fabric placed over plants retains heat and can offer up to several degrees of frost protection. In smaller gardens almost any type of cover, including newspaper cones, miscellaneous bits of plastic, etc, can serve the same purpose.
- Hoop houses: Plastic sheeting is placed over a frame (usually in an arced shape), to create a type of greenhouse. Hoophouses can be large or small, simple or nearly as functional as greenhouses.
- Mulches: Any material placed on the soil around plants will help retain heat. Organic mulches include straw, compost, etc. Synthetic mulches, typically, plastic sheeting with slits through which plants grow, is used extensively in large-scale vegetable growing.
- Raised beds: Beds where the soil has been loosened and piled a few inches to over a foot above the surrounding ground heat up more quickly in spring, allowing earlier planting.
Season extension techniques are most effective when combined with crop varieties selected for the extended growing conditions. Many approaches are used in large-scale agriculture, as well as in small-scale organic farming, and home gardening.
Using unheated, unlit methods, depending on the crop, up to several weeks of productivity can be added, where shortened period of sunlight and cold weather end the growing season.
Season extension can apply to other climates, where conditions other than cold and shortened period of sunlight end the growing year (e.g. a rainy season).