Extending Your Growing Season: Row Covers, Cold Frames & More
The Short Answer
Simple, inexpensive season extension techniques can add 4-8 weeks to your growing season — 2-4 weeks earlier in spring and 2-4 weeks later in fall. Row covers, cold frames, mulch, and wall-of-water protectors are the most practical options for home gardeners. No greenhouse required.
Row Covers (Floating and Supported)
Row cover fabric (also called garden fabric or frost cloth) is a lightweight, translucent material that drapes directly over plants or over wire hoops. It lets light and rain through while raising the temperature underneath by 4-8°F and protecting against light frost.
Lightweight row cover (0.5 oz/sq yd) protects against frost down to about 28°F while letting in 85% of light. Use it in spring to protect transplants and in fall to extend the harvest.
Medium-weight row cover (1.5 oz/sq yd) protects against harder frosts and provides more warmth but lets in less light. Better for fall use when you're trying to keep existing plants alive rather than encouraging new growth.
You can buy row cover fabric at any garden center for a few dollars per row. It's reusable for 2-3 seasons and pays for itself many times over in extended harvests.
Cold Frames
A cold frame is essentially a bottomless box with a transparent lid (glass or polycarbonate) placed over a garden bed. It creates a miniature greenhouse effect — solar heat is trapped inside during the day and slowly released at night.
A simple cold frame can raise temperatures 10-20°F above outdoor ambient temperatures, extending your season by 4-6 weeks on each end. It's one of the most effective season-extension tools available.
You can build a cold frame from an old storm window and scrap lumber, or buy a ready-made one. Place it over your most cold-sensitive plants or use it to harden off seedlings in spring.
Wall-of-Water and Cloches
Wall-of-water protectors are cylindrical, water-filled chambers that surround individual plants (usually tomatoes). The water absorbs solar heat during the day and releases it at night, keeping the plant warm even during freezing temperatures. They can allow transplanting 3-4 weeks earlier than unprotected planting.
Cloches are individual plant covers — anything from a glass jar to a plastic milk jug with the bottom cut off. They provide localized frost protection and warmth. Simple, free (if you're reusing containers), and surprisingly effective.
Mulch
Mulch doesn't raise air temperature, but it moderates soil temperature — keeping it warmer in fall and cooler in spring. A thick layer of straw, leaves, or wood chips over root vegetables like carrots and beets can keep the soil from freezing, allowing you to harvest well into winter in moderate zones.
For garlic and other overwintering crops, 4-6 inches of straw mulch insulates the ground and prevents the freeze-thaw cycles that can heave plants out of the soil.
What's Worth the Effort?
For most home gardeners, lightweight row cover is the single best investment. It's cheap, easy to use, reusable, and protects against the light frosts that end most gardens in fall. Keep a roll in the shed and throw it over your tomatoes when the forecast dips below 36°F — you might get an extra month of tomatoes.