You Don't Need a Greenhouse – These 6 Clever Tricks Help Protect Winter Vegetables From Frost
A greenhouse is nice to have, but your winter crops can get by without one. A few simple, inexpensive tricks can help hardy vegetables survive through winter.
Your greens look great on Sunday afternoon. Then a clear, still night pulls the temperature down hard, and by Monday morning the lettuce has gone dark and limp, and the chard leaves look soft and water-soaked. It's a rough way to lose a bed of winter vegetables you've been tending since late summer, especially when the forecast only mentioned a light frost.
Several of the cold-hardy winter vegetables keep producing through the colder months, and a greenhouse isn't required to help them along. Cheap covers and a little attention on cold evenings go a long way, and a good share of the materials are probably in the garage already.
A handful of frosty nights in November is a different problem from weeks of frozen ground. Light covers can usually handle the first. That second one takes layers – fabric over the plants, mulch over the soil, and sometimes a solid structure on top.
1. Cover Crops with Horticultural Fleece or Frost Blankets
Row covers get sold as frost blankets or horticultural fleece, but it's the same thin spun fabric either way. Light, air, and rain get through. What it holds in is warmth rising from the soil overnight, usually enough to keep lettuce, spinach, kale, and Swiss chard a few degrees warmer than bare beds. Heavy 1.5-ounce (51g/m²) cover holds more heat. It also blocks about half the light, so keep it for cold snaps.
Heat leaks out at the edges, so the cover has to touch the ground all the way around. Boards, bricks, or smooth rocks hold it down. If it sags onto tender leaves, slide a few hoops under it (see section 3). A row or two fits under the Agfabric 1.2-ounce frost cloth from Home Depot, a 10-by-50-foot (3 by 15 m) roll.
2. Make Mini Greenhouses from Plastic Bottles and Milk Jugs
Cut the bottom out of an empty gallon (3.8L) milk jug, and it'll turn into a mini DIY greenhouse for a young lettuce or spinach plant. Smaller seedlings will get by under a soda bottle. Shove the cut edge into the dirt and pile soil around it, or it'll likely end up in the neighbor's yard after the first windy night. Then check that no leaves press on the plastic.
Your jug's cap comes off, too. Sealed up, a jug warms fast on a sunny afternoon, and the seedling can overheat while you're still outside in a jacket. Lift the jugs off on mild, bright days and drop them back on at dusk. If you run short on jugs, reusable clear plastic bell cloches, like these Senwell cloches from Amazon, go on the same way. They come with metal ground stakes to keep them in place.
3. Build a DIY Low Tunnel over Vegetable Beds
Bend flexible ½-inch (1.3 cm) PVC pipe or heavy wire into hoops about 4 feet (1.2 m) apart over a bed, then stretch frost fabric or clear greenhouse plastic across the top. One tunnel can shelter a whole raised bed or a long row of greens. A Haxnicks fleece tunnel from Walmart comes with the steel hoops already attached and stretches to about 10 feet (3 m).
So should it get fabric or plastic? Fabric is the low-fuss choice, since air moves through it and it can stay on for days. Plastic gets warmer in the daytime and sheds rain, but after dark it's no warmer than fabric. Closed plastic can cook the greens on a bright afternoon, so pull up a side or open the ends. Wet, heavy snow can flatten it, too. Snowy areas need sturdier hoops set closer together, plus a brush-off after each storm.
4. Insulate the Soil with Straw or Shredded Leaves
You can leave carrots, parsnips, and other root crops in the bed past fall. Heap straw or shredded leaves on the row, and many of them will keep until you want them. Soil under that pile doesn't freeze as deep or flip between frozen and thawed as often. Left in over winter, a parsnip is, honestly, a sweeter parsnip come spring. Dig the rest before they bolt.
Mulch only protects the soil, though – it won't keep exposed kale or chard leaves from freezing on a hard night, so pair it with a cover. Be picky about the straw, too. Hay and bargain bales can be full of weed seed. GardenStraw wheat straw mulch from Lowe's is filtered, with most of the seed screened out, in a 2-cubic-foot (57L) box.
5. Use an Old Window or Clear Lid to Create a Cold Frame
An old storm window in the garage is halfway to a cold frame. Hinge it to the back of a bottomless wooden box, or right onto a raised bed. Inside, it can run 10 to 20°F (6 to 11°C) warmer than the open garden. Spinach, mâche, and winter lettuce do well in one. Backyard Discovery's cedar cold frame from Walmart has a lid that lifts on its own once the inside passes 70°F (21°C).
Glass is heavy and can break, so secure the pane firmly so a gust can't slam it, and sand any sharp edges. Windows painted before 1978 may also contain lead paint – not something you want flaking into a food bed. On sunny days, heat is the bigger risk, so prop the lid open. Tuck a sensor like this AcuRite wireless thermometer from Lowe's inside the frame, and check it from the house.
6. Move Container-Grown Vegetables into Sheltered Positions
Pots give you an option a bed doesn't. Their weak spot is down in the roots. Those are usually far less cold-hardy than the leaves, and a pot doesn't give them much soil for cover, so a freeze reaches them faster than roots in the ground. Still, you can pick up a pot of parsley, kale, or salad greens and carry it somewhere better. Crowd them by a wall the wind doesn't hit and throw burlap or bubble wrap around the bunch.
Water them well the day before a hard freeze. Wet soil freezes more slowly than dry soil, it turns out. On the bitter nights, carry the smaller ones into an unheated garage or shed. Get them back out the next morning, or once that cold spell is over. Greens left in a dim garage for days can come out pale and leggy.
Which Winter Vegetables Actually Need Frost Protection?
Kale, collards, spinach, parsley, and cabbage can take a lot. Frost under 28°F (-2°C) usually doesn't bother them, but when the forecast calls for low 20°s F (around -6°C), cover them anyway. Lettuce, Swiss chard, beets, and carrots aren't quite as tough. Damage can show up in the mid- to upper 20°s (about -4 to -2°C). Mâche is the odd one out among salad greens and holds up better than lettuce. Beans, peppers, and tomatoes can't take even a light frost.
These ratings aren't fixed, though. Two varieties of the same crop can differ in hardiness, and an established kale plant usually gets through a freeze in better shape than one transplanted last week. Plants that have had several weeks of slowly cooling weather also hold up better than ones hit by a hard freeze after a warm spell. Watch how long the cold lasts, not just how low it'll go.
Winter Vegetable Essentials
A greenhouse would be nice, sure, but straw over the carrots, fabric over the kale, and a couple of milk jugs over the late lettuce will carry a garden a long way. Keep a frost blanket folded by the back door. The night the forecast suddenly drops, it'll be the first thing you reach for.
