For steady winter salads from a cold frame, sow spinach and cold-hardy lettuce about 6 to 8 weeks before your first hard frost, so plants reach full leaf size before days drop below about 10 hours of light. Once days get that short, growth nearly stops until late winter. The frame does not grow new plants in the dark months; it keeps already grown plants alive and harvestable. Timing the sowing is the whole game.
This guide covers the crops and the calendar. If you are still choosing or building a frame, start with cold frame kits for season extension, then come back here to plan what goes in it.
Best varieties for a cold frame
Spinach is the hardiest salad green you can grow. Savoy and semi-savoy types handle cold best:
- Winter Bloomsdale and Giant Winter: classic overwintering spinach with thick, crinkled leaves.
- Space and other smooth-leaf hybrids: easier to wash and resistant to downy mildew.
Lettuce is less hardy than spinach, so choose varieties bred for cold:
- Winter Density: a compact, upright romaine-butterhead cross.
- Arctic King and North Pole: small butterheads that tolerate hard frost under glass.
- Rouge d'Hiver: a red romaine that colors up in cold weather.
Bonus green: mâche (corn salad) is even tougher than spinach and fills gaps between rows.
🌱 Get Personalized Plant Picks
Answer a few quick questions and we’ll match plants to your exact yard conditions.
Find My Plants →Sowing calendar by zone
Count back from your average first hard frost (about 28°F):
- Zones 3 to 4: sow spinach late July to mid August; lettuce early to mid August.
- Zone 5: sow spinach mid to late August; lettuce late August to early September.
- Zones 6 to 7: sow spinach early to mid September; lettuce mid September.
- Zone 8: sow from late September into October. Many Zone 8 gardeners use the frame mainly for hard freezes.
Make a second, later sowing 2 to 3 weeks after the first. Those small plants sit nearly still through the darkest weeks, then take off in late winter for an early spring harvest. See the fall garden guide for Zone 6 for broader timing.
Shop cold-hardy salad seeds and harvest snips on Amazon
Overwintering spinach seed, a mixed lettuce seed pack, and small stainless snips for picking outer leaves. We may earn a commission at no extra cost to you.
Amazon · Spinach seeds for planting Amazon · Lettuce seeds for planting Amazon · Stainless garden snips
Getting seeds to sprout in warm soil
Late summer sowing runs into one problem: spinach and lettuce germinate poorly in soil above about 80°F.
- Sow in the evening and water the bed well first.
- Shade the frame with the lid propped open or a scrap of shade cloth until seedlings are up.
- Prechill spinach seed in the refrigerator for a week before sowing to improve germination.
- Sow thickly and thin later: spinach to 3 to 4 inches apart, lettuce to 6 to 8 inches.
Mix compost into the bed before sowing. A loose, fertile soil gives you bigger plants before the light fades.
Venting: the step most people miss
A closed cold frame in sun heats fast. On a 40°F sunny day, the inside can climb past 90°F within an hour, which wilts lettuce and pushes spinach to bolt in spring.
- Open the lid when the inside reaches about 60 to 65°F. Prop it a few inches on cool days and wider on warm ones.
- Close it by mid afternoon to trap heat for the night.
- Use an automatic vent opener if you are away during the day. A wax cylinder opens the lid as it warms, with no power needed.
- A min and max thermometer inside the frame shows exactly how hot and cold it got while you were gone.
Watering and cold nights
- Water less as days shorten. Check soil weekly; water on a mild morning so leaves dry before night.
- On nights below about 15°F, add a layer of floating row cover over the plants inside the frame. A cover inside the glass adds several degrees of protection. More detail: frost cloth and row covers for the fall garden.
- Brush heavy snow off the lid so light can reach the plants. Light snow along the sides adds insulation.
Shop venting and cold night gear on Amazon
A heat-powered vent opener, floating row cover for the coldest nights, and coated gloves for cold morning harvests. We may earn a commission at no extra cost to you.
Amazon · Automatic vent opener Amazon · Floating row cover Amazon · Nitrile-coated gardening gloves
Harvesting through winter
- Pick outer leaves and leave the center crown to keep producing. Take no more than a third of a plant at a time in the dark months, because regrowth is slow.
- Never harvest frozen leaves. Wait until the frame warms and leaves thaw, or they turn to mush.
- Cut cleanly with small garden snips or scissors. Keep your fingers clear of the blades and close them when you are done. Wear gloves on cold mornings for a better grip.
- Expect a burst of growth in late winter once days pass about 10 hours again.
Pests to watch
Slugs and voles love the shelter of a cold frame. Check under the edges, hand pick slugs on mild evenings, and close gaps at ground level. Aphids can show up on lettuce in a warm spell; rinse them off with water.
Pet notes
Spinach and lettuce do not appear on the ASPCA list of plants toxic to dogs and cats. Spinach is high in oxalates, so plain leaves are a small treat at most. The bigger hazard is slug bait: metaldehyde baits are highly toxic to dogs and cats. Choose iron phosphate products and follow the label. If a pet eats slug bait or anything else of concern, call your veterinarian or the ASPCA Animal Poison Control Center at (888) 426-4435.
Bottom line
Sow spinach and cold-hardy lettuce 6 to 8 weeks before hard frost, follow with a second sowing a few weeks later, vent the frame on every sunny day, and harvest outer leaves only when they are thawed. Get the timing right and the frame will hand you salads through the coldest months.