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Spring can always send us unexpected cold snaps. Use these ways to protect spring crops from the cold to save them from cold, frost, and biting wind. Includes using cloches, row covers, cold frames, greenhouses, and hotbeds.
It’s April, and you may have already begun planting seedlings out. It’s warm, it’s sunny, and you forgot that spring can sometimes give you unwanted surprises. Warm days can turn into a light frost the next morning and if your seedlings get caught out, then you could lose some or all of them to winter’s last breath. You may also be laughing reading this, as you glance out the window to snow still on the ground. Spring can really take her time in arriving if you live in the north. There’s hope for an early start to your garden too.
I’ve put together these tips so that you can protect your garden if need be. That means that if you have crops in the ground that worried about, there are measures you can take to protect them from the cold. You can also use the ideas to get a head start on this year’s crops if it’s still too cold for you to be planting outside. Being a successful gardener in any climate comes down to being flexible, inventive, and understanding what plants need. You’ll have challenges every year, but adding to your knowledge of what to do will keep you prepared for most circumstances. Even a cold spring.
Soil and Air Temperature
The main reason that you wouldn’t plant most seeds or plants in the ground during the winter or a cold spring is that it’s, well, cold. Wild seeds that are in the soil outside remain dormant until the soil temperature is just right, generally 60-86°F (15-30°C). After that point, they know that spring is finally here, and they’ll start rearing their heads above the soil. Most edible crops are the same, and if you sow them too early, some may rot in the ground. Others might be eaten by wildlife as seeds or tiny seedlings.
Some vegetables germinate at and tolerate lower temperatures, down to 40°F (4°C), which is why spring crops tend to consist of lettuce, spinach, peas, broad beans, and spring cabbage. Summer crops like tomatoes, eggplant, and squash need a lot more warmth from both the soil and the sun. Put them outside too early, or without hardening off, and they may die. There may not be much you can do about those if you’ve made that gardening mistake, but if your plants are hardier, and cold weather is nigh, you may be able to safe them.
The tips below are ways that you can protect seedlings and plants that you’ve already planted out. If it’s a cold start to the year and you can wait on sowing, use the sowing tips at the bottom of this piece.
Warming the Soil with Black Plastic
If you have an outdoor garden and want to help the soil warm up quicker, you can cover it with black polythene plastic. In winter, lay the plastic over an entire bed and pin it down with stakes or weights. Leave it there until spring and it will not only keep the soil drier and kill off weeds but will absorb the sun’s warmth. The soil underneath will warm up a lot quicker than exposed soil. In spring, you can either cut holes in the plastic and plant through it or remove the plastic and store it away for its next use. Once crops are in the soil, you can protect them with cloches and row covers.
Use Cloches to Protect Spring Crops from the Cold
This time of the year, it’s calm and warm inside my greenhouse but step outside, and it’s cold and breezy. Cloches and clear-plastic row covers work in the same way as a greenhouse – they capture the warmth of the sun and keep the wind out. In the past, cloches were bell-shaped glass objects that you placed over individual plants.
These days, they tend to be plastic, and you can even use recycled materials to create your own. Drink bottles work well for this and include the plastic two-liter bottles that fizzy drinks come in, as well as plastic milk containers, large plastic water bottles, and even gigantic water bottles for water dispensers.
Use Row Covers to Plants from the Cold
Row covers can work in the same way as a cloche but cover entire rows of crops. It could be a sheet of white horticultural fleece that you lay directly over an outdoor bed of seedlings. You could also drape the same material, or clear plastic, on supports over the crops.
Supports tend to be rounded hoops since they won’t poke holes in the material, but you can find squared-off hoops too – I have both. In summer, I use the same hoops to drape netting over. It helps keep birds, rabbits, and other wildlife from eating my crops.
Hooped row covers also come ready-made and are a great way to protect spring crops from the cold. They tend to cover only a single row of crops at a time and are made from horticultural fleece or clear plastic that’s embedded with wire hoops that you press into the ground.
Start Seeds on a Hotbed
A hotbed is a naturally-heated growing structure that you build outside or within a cold-frame or large greenhouse. The heat comes from fresh manure that, when piled together, generates a lot of heat. Imagine how warm a pile of fresh grass clippings gets if you leave it piled somewhere in the garden – it’s the same principle.
If you have space, build a container at least 3 feet wide, long, and deep. Fill it with a mixture of fresh horse manure and straw and then grow your seeds and plants in modules or trays on the top. The heat from the rotting manure will warm the modules from the bottom, just like an electric propagator, and lasts for up to two months. In the summer, you can grow pumpkins and other vegetables in the, now, composted manure.
Growing in a Cold Frame
Cold-frames are a valuable tool throughout the growing year – they’re a mid-way point for plants grown undercover and being prepared for the great outdoors. They have four sides, generally made of wood or brick, and a top that’s made of glass or clear plastic. The best place to build a cold frame is against a south-facing wall for even more warmth.
The top is set at an angle so that it can capture more light, and that rain runs off. That means that the box it covers is higher at the back than in the front.
The shelter they provide is not quite as warm as a greenhouse or house, but not as cold and breezy as the garden. They’re where you harden off your seedlings. Use cold-frames to grow early crops of lettuce and spinach or to sow cold-hardy seeds like broad beans. The structure will protect the plants inside from wind, frost, and snow.
Grow in a Cold Frame Hotbed
If you have the time and resources, you could also convert a cold frame into a mini-hot bed. Create one by setting the cold frame over ground that has been dug out and filled in with 18” of manure then covered with 6” of compost. The heat from the manure starts seeds germinating, and the cold-frame works like a small greenhouse.
This method was used extensively in Victorian kitchen gardens to produce early crops for the folks in the big house. They were also a popular way to grow tender crops like melons in cool-climate Britain. In cooler climates, you protect both summer and spring crops from the cold.
Choose the Right Varieties for Spring
If the spring has been cold and you’re waiting longer to sow, opt for quicker growing vegetables. Smaller varieties, like dwarf peas, will produce pods a lot quicker than pea varieties that grow taller. This year I’m growing ‘Meteor,’ a dwarf pea that only grows about 18” tall. I’m also growing a more traditional pea variety because I’m an optimistic gardener! There are countless cool-season and dwarf vegetable varieties to choose from, so hedge your bets by growing at least one, if not two, or three types.
Quick growing edibles like radishes, lettuce, and green salad leaves produce crops in 4-6 weeks. Grow them in an unheated greenhouse or cold-frame, or sow them a little later, and you’ll have a harvest in no time. It’s also practically effortless to grow baby salad leaves and an excellent idea for any time of the year, warm or cold.
Greenhouse and Polytunnel Growing
Not everyone has space or budget for a greenhouse or polytunnel, but they’re another option for ensuring a harvest. Enclosing an area with glass or plastic creates a warm micro-climate inside, and though I don’t heat my greenhouse, it stays relatively mild right through the winter. I grow greens in mine and overwinter tender plants that are in pots.
Greenhouses come in various sizes and materials, and you can even order them online. Polytunnels are large plastic-covered hoops, and they also come in different sizes. They’re very similar to the hoop row-covers in structure but far sturdier.
Wait on Sowing Seeds
If at all possible, just wait on sowing seeds or buying plants. First of all, the sowing instructions on the backs of seed packets are often misleading. In many cases, the same seed packet will end up in the hands of people in wildly different regions, from Maine to Florida or from Scotland to the Channel Islands. Spring will arrive sooner if you’re closer to the equator, and sowing times will differ based on your region’s temperature and last frost date.
In a good year, you should stick to sowing guides for your specific area. In a cold one, you may need to disregard the rules and start seeds a week or three later. Keep in mind that seeds sown a little later will quickly catch up. Seeds sown too early can be sickly and be less productive. Many seeds need to feel warmth to germinate, so if you sow them in cold soil, they probably won’t grow. If you live in a place with particularly cold springs or want to get a head-start on growing seedlings, the best way to do it is indoors.
Starting Seeds Undercover
Regardless of whether it’s a typical or cold spring, I tend to start many of my seeds undercover. That means sowing seeds into trays or modules, and growing them someplace warm and out of the elements. That may be my grow-light set-up, electric propagator, a cold frame, greenhouse, or a sunny window sill.
If I start seeds on my window sill, I also attach my clip-on grow-light to stop the seedlings from trying to stretch towards the side-light. ‘Leggy’ seedlings often end up much weaker than plants that have proper overhead lighting. With proper grow lights you can keep your plants indoors for longer, without worrying about whether they’re becoming unhealthy.
When to Sow Seeds
The way I judge when it’s time to sow seeds is to add together the days that a seed needs to germinate, along with the weeks it can hang out inside before needing to be planted outside. With lettuce, it’s about a month. Then I work out what my region’s last frost date is, and sow at most, that amount of time from that date. My last frost date on the Isle of Man is the 31st of March, so I can begin sowing lettuce and a few other greens at the end of February. I’ll sow more seeds every two weeks after that for a steady supply of salad. If your spring is cold, keep your seedlings inside for an extra week or two. You can also wait on sowing seeds.