I don’t know about you, but I tend to be a bit impatient when it comes to getting the spring garden started. After a couple of months’ rest from garden chores through the holidays, I find I’m eager to dig in the dirt again and start the whole process of growing our family’s food for another year. Unfortunately, my timing and Mother Nature’s timing aren’t exactly on the same page. So, I cheat a bit and use cold frames to extend our season by several weeks. And the good thing about cold frames is they don’t have to be expensive and can be built from many of the items you may already have around you own place.
One of the biggest things to remember when building a cold frame is that the goal is not to create summer-like conditions. Instead, the function of cold frames is to reduce or eliminate the freeze/thaw cycles common during spring (or winter) by collecting solar heat during the day, blocking chilling winds, and deflecting cold, soaking rains. By reducing the impact of each of these environmental factors, a well designed cold frame will often keep temps inside around 10°-20°F above outside temps depending on materials used.
Now, if your family is like ours, you’re probably about as busy as you need to be. So, the good news is cold frames are simple to build, being essentially nothing more than a bottomless box with a lid. When designing your own frame, you want to create a bottomless box with sides reaching 12”-18” in back, about 8” in front, and as long as your needs require. These dimensions create a frame with one side being higher than the other. This slanted top provides optimal solar heat acquisition as the sloped angle allows the sun’s rays to hit directly into the box during much of the day. However, it is not entirely necessary to create this slanted surface as long as placement of the frame is in full sun. Just know that you may not achieve temperatures quite as warm as you would otherwise.
To build your cold frame, use what’s on hand to keep costs down, especially when building your first one. For the sides, use scrap untreated lumber, bricks, masonry blocks or even hay bales if you happen to have any extra. To create the light (or lid) you’ll need some type of translucent material to allow the sun’s rays to enter the box. Recycle old storm doors or windows, shower doors, salvaged greenhouse panels, Lexan, or other clear material to further increase savings. If none of these materials are available, use heavy duty plastic sheeting instead. You can build a frame for the sheeting or simply drape it across the box and secure with blocks, water jugs, or other heavy items to prevent heat escaping. Once you see how well you like the convenience of extending your growing season, you may do like we did and choose to build a longer lasting version with sturdier materials.
Choosing a site couldn’t be easier. Walk your garden and select the sunniest spot available. Check to ensure it’s not in a low place that collects rain water, as cold, spring rains pooling under the frame will spoil your plantings. It is also beneficial to place the frame in an area with wind protection, such as near shrubs or other tall plantings provided they do not block valuable sunlight. However, temporary wind protection can be created by stacking hay bales or other large items along the windward side of the frame in the event of especially cold and windy days.
While you want to keep heat in, there will be times when you have to ventilate excess heat. Keep a thermometer in the center and monitor throughout the day until you get the feel of when to vent. In most cases, outside temperatures of 20°F and higher require venting for at least part of the day when growing cool season plants like lettuce and spinach. If you’re using your cold frame to harden off heat loving seedlings, you may need to leave the lid closed until temperatures are a little closer to 45°F. Regardless of what you place inside the frame, you may need to lift the light only a few inches when temperatures are on the lower end of the temperature range while warmer weather will call for wider openings.
If your spring weather is like ours, you know to expect what we call ‘blackberry winter’ right before spring officially sets in. This is the time that the kids are running around in shorts and tank tops one day only to discover snow on the ground the next. During these exceptionally cold spells, you may need to provide additional, temporary insulation. When temps drop into the single digits, add extra insulation by placing a heavy blanket or several inches of hay across the top and sides. Just be sure to remove during the day when temps rise to avoid overheating.
When I first discovered cold frames several years ago, I was instantly hooked. These nifty season extenders not only allowed me to play in the dirt earlier than ever before, but they have given our family yet another tool that allows us to provide ourselves with even more home grown food rather than relying on the grocery store. And with a little creativity, we’ve found we can easily add an extra frame or two when the need arises without overly extending our budget. Once we see a more permanent cold frame is needed, we then budget the materials in and build one that will last for many years to come.
Now that is sustainable living!