Cold Frame Tips for Preppers


The first few years I grew tomatoes, the plants got big enough that the little tomatoes formed, and then the hottest days of summer hit. When it gets into the 90’s and 100’s in Utah, tomatoes stop growing. They don’t start growing again until the weather drops to the 80’s in the late summer and early fall. As a result, tomatoes don’t ripen until just about the first tomato-killing frost.

Having no tomatoes until just before the frost doesn’t put food on the table for an entire summer. I might as when just use freeze dried tomatoes if I can’t get a longer harvest season.

I thought about jumpstarting my tomatoes by sprouting them inside under grow lights in late winter or early spring. However, growing plants under electric lights seems to be against all my prepping instincts. Grow lights don’t work when there is no power.

My second option was buying or building a small greenhouse. We have strong winds in Woods Cross, so I’d need to spend some money to have a greenhouse that wouldn’t collapse or blow away. The price was just too much for me.

Finally, I learned about cold frames. Cold frames are mini knee-high greenhouses. I realized that Cold frames were the tomato seedling growing tool I needed.

Start your growing season a month early by using coldframes.

Many people choose to build their own coldframes, to avoid expense. A combination of old windows, and a few boards can result in a beautiful and solid cold frame.

I wish I had those skills. I went with manufactured cold frames by Jewel. They’re fairly strong and have lasted me several years. They required some assembly, but not more than I felt comfortable with.

I love my cold frames. However, learning to use them properly took years of experimentation. Cold frames don’t automatically ensure quicker or earlier growing seedlings and plants. I lost a lot of plants to my early ignorance.

The placing of cold frames is the first step to proper use of cold frames. Cold frames need sun all day. That sounds easy, but if you set up your cold frames in the summer, the shadows cast by houses, trees and fences are very different than in the early spring when you want to use your cold frames. It is very easy to place your cold frame in full sun when setting it up, and find that it only gets partial sun (or no sun) at a different time of year.

I had a farmer friend of mine explain several years ago that plants that get morning sun do better than plants that only get noon or afternoon sun. I’ve found this true for plants in cold frames, too. If you need to select a location from several that only get partial sun, favor the location that gets the earliest morning sun. The plants will love you for it.

When setting up your cold frame, find (or create) a spot with level ground. Pots, plants, and bottles used for temperature regulation will tip over on even small slants. Make the area for your cold frame as flat as possible.

A great way to level ground for your cold frame is to take a tiller to it to break up sod and packed dirt. Then go at it with a garden rake. Leveling freshly tilled ground is child’s play.

Cold frames promote plant growth in early spring. This is great for your potted plants and seedling trays. Unfortunately, it is also great for every weed or blade of grass ever sprouted in the dirt under the cold frame. Before finalizing the position of your cold frame, lay down a few layers of weed blocking cloth. It won’t prevent all weeds, but it might slow them down for a season or two.

Anchoring a cold frame to the ground is very important to keep it from being destroyed by windstorms. Before anchoring your cold frame, make sure it is squared properly. Crooked cold frames prevent lids from opening and shutting easily, and in the worst cases, the top windows won’t open or shut at all. The easiest way to ensure a cold frame is square is by putting the lids on and closing them up. Having the cold frame fully assembled squares it the quick and easy way.  Check that the top windows open and close properly before anchoring the cold frame to the ground.

Never place your cold frame under tree branches. Even though the slanted sun of spring may hit the cold frame all day, the cold frame will constantly be covered with bird droppings and anything your tree sheds during its spring pollination process. Clearing the top windows of the cold frame will become a full-time job. Watch out for those tree branches.

Mound a couple of inches of soil around the edge of your cold frame. This keeps cold night air from seeping under the bottom of the cold frame. This also slows down harmful seedling-munching bugs and mice from getting to your sprouts. An inch or two of dirt is usually enough insulation around the bottom of the cold frame.

If you are like me, you’re busy. However, on days that warm up quickly in the spring, you need to open up the top windows of the cold frame to avoid frying your seedling and plants. We’ve all got into a car that was left out in the sun. Cold frames warm up just the same way as a car in the sun. Warm air is good for your plants, but hot air kills them.

I’ve found having a self-opening window helpful on those days I forget to vent my cold frames. It is a seedling saver. Good automated vent openers do not require batteries. They are heat activated, and well worth their cost. Forgetting to open your cold frame even one time can destroy weeks of hard work.

Remember to keep the plants in your cold frame well watered. They will dry out quicker than plants in your yard or house. The cold frames will stay warmer than your house, and have full sun. Soil in pots and seedling trays in the cold frame will dry out quickly.

Regulating temperature in the cold frame helps your plants. The corners of your cold frame are most susceptible to extremes in temperature. At night, the corners get the coldest, and at noon the corners get the hottest.

Two easy tricks for keeping temperatures from reaching extremes at noon and midnight in your cold frame involve bricks and water bottles. I like to line the corners of my cold frames with sunlight absorbing bricks. They absorb excess heat in the daytime, and release that heat when it is needed at night.

I usually place several bottle of water in my cold frames, too. I repurpose old soda bottles and orange juice bottles—cleaning them and filling them with water. After filling the bottles with water, I spray paint them black to encourage absorption of heat from light. I place the bottles evenly around the edges of the inside of the cold frame on my bricks. The corners are the first place I put the bottles and then evenly space the rest along the longer sides of the cold frame.

Just a note, … I don’t use old milk jugs for my cold frames. The reason is that the plastic they use in milk jugs becomes brittle after about six months to a year, then cracks or splits. I’ve found pop bottles and juice bottles to be longer lasting.

No matter how hard you try to prevent it, harmful bugs will get into your cold frame. You never see those bugs, but you always see your dead seedlings in the morning. Putting poison on young plants inhibits their growth and often kills them. The solution I’ve found is to spread a thin layer of bug killing powder under the plant pots and seedling trays. It turns out that the harmful bugs often hide out under the trays and pots during the daytime. Setting the pots and trays on the poison often wipes out the harmful bug population in the cold frame.

Finally, when the nights are warm enough, take your top windows off the cold frame. When the nights are warm enough, the cold frame’s work is done.

All that information represents years of experimentation. You can’t learn to be a prepper overnight. Prepping takes practice! Hopefully, you get something useful out of it. If you like this post, remember to share the link!


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