When to use a garden cloche falls into four main windows each year. The first is early spring to warm soil before sowing. The second is during late-spring cold snaps that threaten tender plants. The third is in fall to extend the harvest. The fourth is winter for hardy greens in mild zones.
I have kept calendar notes on cloche use for five growing seasons now. The pattern is clear. My spring cloches go on March 1 in zone 5. They come off by early May. My fall cloches go on mid-September. They stay on till hard frost ends growth around mid-November.
Spring cloche use starts before any seed goes in the soil. Place the empty cloche on bare soil 10 to 14 days before you plan to sow. The Royal Horticultural Society uses this trick on cold UK soil with great results. The soil hits 50°F (10°C) under the cover by sowing day.
Sow your seeds right under the warm cloche when the soil is ready. The cover then protects the new seedlings from frost, wind, and pests. Keep it on for 3 to 4 more weeks after the seeds sprout. This is the heart of spring cloche timing for cool-season crops like lettuce, peas, and spinach.
Set out warm-season starts under cloches 2 to 4 weeks before your local last frost date. Tomato, pepper, and squash starts can go in this early under cover. The cover holds night soil temps above 45°F (7°C) even when outside air drops to 32°F (0°C). Your starts gain weeks of growth.
Late-spring cold snaps are the second key use window. A clear forecast for 28°F (-2°C) in May after you set out tomatoes can wipe out the whole bed in one night. Pop a cloche over each plant by dusk. Pull it off the next morning when the air warms up again.
Utah State Extension says to take cloches off once daytime highs stay above 60°F (15.5°C) for a week. Past that point, your plants get more harm than help from the trapped heat. Most home gardens hit that mark by mid-May in zone 5 and late April in zone 7.
Fall cloche use kicks in once nights start to cool down. The first frost forecast is your trigger. Pop cloches over your most prized late crops by mid-September in zone 5. Hardy crops like kale, chard, and spinach can keep growing under cover for 4 to 6 more weeks.
Fall is the most rewarding cloche window for many growers. You get fresh salad and greens long after your neighbors give up for the year. I logged 6 extra weeks of fresh lettuce in 2022 using cloches alone. The trick is to start covering before the first frost hits, not after.
Winter cloche use only works in mild zones or for the hardiest crops. Zone 7 and warmer can grow mache, claytonia, and winter spinach under cover all season long. Zone 5 and colder need a cold frame, not a cloche, for any real winter harvest.
Hardy greens under a cloche need vent checks even in winter. A sunny day at 35°F (2°C) outside can heat the inside to 65°F (18°C) by noon. Tilt the cloche on its side to let warm air out. Set it back at dusk to hold the night warmth in.
Build your own cloche calendar around two key dates. Your local average last frost date sets the start of spring use. Your local average first frost date sets the start of fall use. Count backward 2 to 4 weeks from each date to plan cloche-on days. Mark them on a paper or phone calendar.
Zone 5 first frost dates fall around October 10. Last frost dates fall around May 10. Zone 7 dates run 3 to 4 weeks later in fall and earlier in spring. Find your own dates on the NOAA frost map. Use those dates to anchor every other cloche choice you make.
Read the full article: Garden Cloche Guide: 7 Best Uses
