Extending the Growing Season: Row Covers, Cold Frames, and Low Tunnels Compared

Season extension tools trade cost and complexity for degrees of frost protection and weeks of extra growing time. Matching the tool to the actual need — a light frost buffer versus a genuine mini-greenhouse — avoids overspending on protection a crop does not need.

The main options compared

Row cover: the simplest and cheapest option

Floating row cover is a lightweight spun fabric laid directly over crops or supported on hoops. It lets light and water through while trapping a few degrees of warmth and, as a side benefit, excludes many flying pests. It is the standard tool for protecting a marginal frost night or for pushing cool-season crops a few weeks earlier or later.

Cold frames suit seedlings and low-growing crops

A cold frame is essentially a bottomless box with a transparent lid set directly on the ground, capturing solar heat during the day and slowing heat loss at night. It is ideal for hardening off seedlings before transplant and for overwintering hardy greens like spinach or mâche, but the lid needs venting on sunny days even in winter, since trapped heat can build quickly and overheat or scorch plants.

Low tunnels for row-scale extension

A low tunnel — wire or plastic hoops covered in row cover or greenhouse plastic — extends the growing season for a full row rather than a single bed's worth of seedlings. Doubling up a layer of row cover under plastic sheeting on a low tunnel adds meaningfully more frost protection than either layer alone, which matters for pushing hardy crops through real winter cold rather than just a light frost.

Which crops benefit most

• Cold-hardy greens (spinach, kale, mâche, arugula) extend well into and sometimes through winter under a low tunnel or cold frame.
• Root crops like carrots can be left in the ground under heavy mulch and a cover, harvested through much of winter in many climates.
• Frost-tender crops like tomatoes gain only a modest window at each end of the season — enough to save a crop from an unexpected early frost, not to grow through real winter cold.