Growing in a cold frame is a great way to extend the growing season. Cold frames allow you to start your plants earlier and keep plants growing later by protecting them from frosts. Find out how to build a cheap cold frame that will save you money each year!
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Cold frames are a versatile gardening tool which are primarily used for cold weather crops such as mache, kale, arugula rather than tender warm crops such as tomatoes, eggplant and peppers.
How to build a cheap cold frame
Building a cold frame isn’t expensive and you can easily build one to suit your budget. You can build one with a plastic sheet and some bricks or an old glass window and some straw or hay bales.
This cold frame was made using plastic packaging and bricks laying around the yard.
Straw bales make great cold frame walls because of their insulative qualities and you can use them in the garden after you are done with the cold frame or even grow directly in the bale.
Sunken cold frames made with concrete blocks (breeze blocks to us Brits) as the walls then covered with a clear cover such as an old window, Plexiglass (Perspex), old glass door or clear plastic stapled to a simple wooden frame can be an inexpensive cold frame to plant in. The holes in the blocks can be filled with plastic packaging to act as insulation.
I got a little fancy and convinced my husband to “show me how to build a cold frame” but really he designed and built it with me helping with the nail gun! We built ours using a glass door that I picked up from the Habitat For Humanity Restore in Salt Lake City. I picked this door up for $5. We could have saved even more money by using salvaged wood but we (he) chose to purchase the wood and hardware supplies new.
You can see step by step how we built the cold frame above in my previous post, How to Make a Cold Frame.
How about Erica at Owning Burton Farm?
What cold frame set up does she use? Let’s ask her and find out!
So back in 2012 when we were dating and my now husband must have wanted to impress me, Clint designed and constructed a raised planter that followed the steep slope of the driveway at the town house where I lived. We grew massive quantities of lettuce and basil, a few tomatoes & purple carrots, and maybe one cucumber. Then we had the boys, bought our farm, and moved to the next town.
I was sad to leave our townhouse, and my convenient planter. While we were dreaming up our garden here at the new Burton farm, we decided maybe the raised bed was not helping the townhouse sell, so my husband deconstructed it and brought it to the farm, where it sat for several months until he reimagined it with some old window frames as this cold frame/planter. The windows are not permanently affixed so we can just take them off whenever we want to get more air circulation.
Right now we have swiss chard and spinach growing beautifully. The boys like to pick off the spinach leaves and eat them right out of the garden. I’m so excited they get to see us re-purposing old things into new ones, as well as gaining the understanding how food grows.
Types of cold frame
Yes folks there are different types of cold frame or season extenders available from the row covers below…
To the unheated greenhouse and everything in between.
Cloches are mini greenhouses made from plastic bottles with the bottoms cut off, glass bell jars or demijohns and carboys which have the bottoms removed either accidentally during cleaning or on purpose.
Cloches such as these offer another benefit by protecting your precious seedlings from slugs, snails and other critters which will munch on your crop.
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How does a cold frame save you money later?
Cold frames are used to extend the season. This means that they protect your crops from frosts and snow. If you plant cold weather crops in them, they will grow slowly allowing you to pick fresh throughout the winter and get a head start on spring if you let them keep growing.
Cold frames require no external heating and are heated with passive solar energy so you don’t need to spend money in heating them.
A cold frame means you can still be harvesting fresh, nutritious veggies for longer which means you are buying less at the grocery store.
A cold frame can extend the season by about 6 weeks in most climates in both spring and fall. In more mild climates like my homeland (England) you can keep growing throughout the whole season with a wee bit of planning.
Basically, a cold frame lets you grow more food!
7 Ways to use your cold frame
Hardening seedlings is the process of getting your seedlings ready for transplanting by exposing them to cooler temperatures during the day then covering them back up over night.
Improper hardening off can stunt plant growth or even kill your seedlings.
Overwinter plants and cuttings
Some plants need to be protected from plummeting winter temperatures and can be kept dormant in a cold frame then planted out in spring.
Hardwood cuttings from evergreen or deciduous plants can be placed in the cold frame to root over winter. Come spring signs of growth will be apparent and the rooted cuttings can be transplanted.
Start seedlings early
Vegetables and summer flowers can be sown weeks ahead of the final frost date in a cold frame whether in seed trays and flats or in soil inside the cold frame.
Nursery bed for softwood cuttings
Don’t dismantle your cold frame! Softwood cuttings such as geraniums, fuchsias or chrysanthemums taken in summer can be placed in the cold frame as a protected nursery or starter bed. The cuttings will be safe from disturbance and should be able to take root.
Start cold weather crops in a cold frame to grow over fall and winter. The cold frame will keep your plants warmer and growing slowly throughout the cold season.
Also known as a hot frame, this technique was popular in Victorian England and French market gardeners. They force early growth with heat from the soil which is created by partially rotted farmyard manure or compost underneath the soil which the seedlings are sown into.
Cold frames can allow you to start your more exotic vegetables up to 3 weeks earlier.
When you sow your warm weather plants like tomatoes, chilies, eggplant (aubergine), okra or ground cherry (physalis) place a cold frame in the area you will be planting to get the soil warming up ready for transplanting. Mulch or black plastic will help reduce weeds from sprouting in the warming soil. When the soil temperature is 70°F you can start hardening off your seedlings and plant your warm weather crops. Keep the cover in place until temperatures outside are high enough (75-80°F). Be sure to vent the cold frame, a sunny day can cause temperatures in the cold frame to exceed 100°F!
7 Top Tips To Help You Get The Very Best From Your Cold Frame
Insulate when very cold
The majority of heat escapes through the glass, so place insulation on top. You can use old blankets, straw, bubble-wrap, cardboard, old scraps of carpet, that nasty duvet the dog was using until he chewed it…… If you live in an area where it snows, that can act as an insulator too. Take care to brush heavy snow off the glass so it doesn’t break
Polystyrene or Styrofoam packaging can be used to insulate the walls of your cold frame or save those coolers to put pots of plants into inside the cold frame.
Blistering heat from direct sun can fry your delicate seedlings. Prop open the lid on hot days and water to ensure your plants don’t die off from excessive heat.
When outdoor temperatures are above 40°F prop open the lid about 6 inches. When the outdoor temperature is above 50°F degrees but below 65°F remove the lid during the day but replace the lid in late afternoon to trap the heat inside for the cooler night.
As a general rule of thumb, open the lid during the day and close it in the early evening to provide ventilation and stop your plants overheating.
An outdoor thermometer can help you get the best from your cold frame by allowing you to see the temperature. You can place one outside where you can easily see it and one in the cold frame for reference.
Place your cold frame where it will get plenty of light. A south-facing position is best.
If you are planting directly into the cold frame, not into pots and seed flats,you need to give your seeds a good start. Add plenty of compost to build the humus in the soil.
You need to let the heat out and the moisture build up in the cold frame to reduce disease. This helps to ensure your plants will be at their best.
Keep the soil damp like a wrung out sponge. High heat and dry soil will kill off your plants.
Bottles of water absorb heat during the day and will release the heat to the surrounding soil and seedlings during the night helping to maintain temperatures in the cold frame. Painting the bottles black will retain more heat.
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Do you use a cold frame? What tips can you share to help other gardeners get the most out of using a cold frame? Please share your tips in the comments or at the Misfit Gardening Community Forum, we would love to hear your ideas and tips.