Extend your growing season (No Greenhouse Required)
I’ve always been told you can’t plant tomatoes in March. I think that’s great advice, but this year, I wanted to push my limits a little, so I built a couple of raised garden beds with a polycarbonate lid that instantly converts them into cold frames.
If you’ve followed me for any length of time you know I’m an avid gardener and always testing my limits when it comes to growing food. From learning how to fix your soil to building your own compost tea brewer (plus this awesome compost tea recipe), I’m constantly sharing my projects, for better or for worse, to inspire you to take action!
A cold frame can be a super cheap and easy garden project that can extend your growing season by a few weeks (or even months) both in the spring and fall, these cold frames are the bomb dot com. They’re a bit more rustic in nature than my easy DIY planter box tutorial, but they’re extremely useful for planting extra crops before or after the “recommended” time (check out my post on when to plant a garden - it’s not too early OR too late!).
Incidentally, they solved a whole lot of other problems besides cold weather for me too (weeds, watering, soil quality). And to top it all off, between the polycarbonate top, recycled screws, and using 4 boards, I was all in for about $28 per box with this project. You can’t beat that!
Pro Tip: If there is a sawmill near you that deals with cedar, such as Grant’s Cedar Mill here in TN, you can buy a bunk (approximately 2 pickup truck loads) of cedar for about $200.
With the price of wood these days, it’s important to be thrifty when you can, and garden projects are a great way to do that. Big box stores sell lumber that’s been kiln-dried, the drying process being important for building with precision (because wood shrinks when it dries), but one of the joys of building things for the garden is that we don’t need much precision.
There is a disease that’s wiping out cedar species across the nation, so most cedar mills are trying to saw up and sell all the wood they can while it’s still useable, which makes for bargain-basement prices.
Get an EVEN BETTER deal on buying bunks of seconds, like this one, (The photo above is a half bundle or $100 worth of cedar), the only downside being that the wood is of various thicknesses and dimensions, so you have to get a little creative with your building techniques, but once again, for a garden, this is perfect, cheap wood.
And hey, once you’ve prettied the space up with plants, even the fine craftsman in me, who winces at tolerances of 1/4” rather than 1/32”, is super happy about the way these cedar boxes improve the space visually.
Quick and Easy Cold frames
The first line of business was to build the base frame that will be filled with dirt. These are essentially bottomless raised beds and can be used as such during most of the growing season. The addition of the top frame will help to get plants in the ground before the last frost, as well as protect the plants at the end of the season when the threat of frost is present.
Building the base frame
I picked 4 boards that were approximately the same width and thickness to construct the boxes.
I cut two feet off each end and used each of those 2-foot cutoffs as the end pieces for the boxes.
I found 4 scraps of 4x4’s to make up the corners of the boxes, then nailed it all together.
The extra width from the 4x4s at the corners of the boxes adds a ton of rigidity and strength to the frame. Just butting up the ends of the boards and nailing them without these 4x4s would make these pretty fragile.
Easy peasy, lemon squeezy. In all honesty, the hardest part of this whole project was moving the boxes.
I built them on the concrete floor of my new school building so I could build on a level surface, but it turns out the wet cedar was really heavy when the whole box was together, and, of course, I picked a super windy day to try to move this stuff.
building the top frame
The top frame will come in handy in early spring as well as in the fall to protect crops from the threat of frost.
The top frame is made of some thicker pieces of cedar. I ripped them all to the same width on the table saw so, when assembled, the frame would sit flush on the top of the raised bed.
I cut a 4x8 sheet of Onduline Tufftex, a multiwall polycarbonate product that is UV resistant, ($53 a sheet at most home stores, yields 2 of these cold frames). I was able to cut the polycarbonate panel with a jigsaw, a circular saw or bandsaw would work fine too.
I secured it to the top of the cedar frame using metal roofing screws which have a little rubber grommet on them.
Testing the Cold Frames
Though this is such an easy project, the proof is definitely in the pudding as far as their usefulness goes. I planted my tomatoes in March, and they survived multiple below freezing nights in these cold frames.
For what it’s worth, while a couple of my hot pepper plants and basil did have a couple of damaged leaves after one particularly cold snap, their roots and plant structure remained unharmed. I simply pulled off the damaged leaves and they regenerated their leaf growth within about a week.
To monitor the temperature during those cold nights, I put a compost thermometer in the beds, and even when it was 28 degrees, the stored heat from the soil, captured within the multi-wall polycarbonate, and the lack of wind inside the sealed box raised the nighttime temperature in the box a full 10-15 degrees, which is A LOT when you’re talking about extending your growing season.
These boxes also came in pretty handy for another reason- being raised off the ground, our persistent battle with crabgrass was (at least temporarily) abated. I was also able to have a lot more control over the soil contents, amending as I built it up.
Keeping the lid on when it’s cool enough to do so also helps retain moisture. That, combined with a thick layer of screened mulch on top of the soil makes watering these boxes a very rare feat indeed.
To add a little more heat, I put a layer of compost at the bottom of the bed. On days I know it will be cold at night, I put the lid on in the late afternoon so I can store up a little extra heat in the soil of the bed.
Have you ever used cold frames? Tell me about your experience in the comments below! And I’d love to see your cold-frame builds, so snap a photo and tag me on social media @anneofalltrades.