Simple cold frame covers can help short-season gardeners warm the soil before planting, harden off tender seedlings, permit an earlier spring plant-out, and protect against early fall frosts. |
Spring Snow: May 10, 2008. Cold frame covers were
in place to warm the soil. Thankfully
nothing was planted inside yet! |
| These mini-hoop frames were made from four pieces of 10' long half-inch pvc pipe fitted inside a 4' x 8' wood raised bed frame. The optional wood framing inside adds stability and provides the basis for plant support later on. |
The stressed tomatoes in this June 4 picture survived a May 26 freeze inside their little huts (which were well-covered at the time).
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| Here you can see how I secured the pvc pipe with an EMT strap (check the electrical section of your home improvement or hardware store) secured to the wood frame. You can also see the poly-latch & wiggle-wire system I attached to the long end of the wood frame for securing the plastic cover. |
Long live wiggle wire! It's a worthy match for our blustery North Dakota winds. Honest!
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| The first year I used this system, I closed the ends of with some "recycled" storm windows I found somewhere. The wind protection helped, but there was quite a bit of air leakage. Here's the endpiece I created for season #2 in its trial fitting. I put more poly-latch and wiggle wire on the sides, hinged a top vent to avoid cooking the plants on a warm day, and secured the ends with a bungee cord tied off to a length of rope. The plasic in this picture is 4 mil from the home improvement store; it's just a bit too short. |
That's translucent ripstop on the ends.
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| Here's the mini-hoop house in action on a cool spring day. I'd replaced the plastic with 6 mil greenhouse grade film, slightly longer to provide a secure fit into the end panels. This set-up will raise the temperatures around your plants on a sunny day (watch you don't cook them), protect against wind, buffer against cool nights, and protect against light frost. If temps dip below freezing, be prepared to take action. For our late-May freeze this year, I draped a large blanket over top of the whole frame as you see it to add insulation. |
See the big frame in the background? It's big enough to stand up inside! Still working out the doors and cover...
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| Just a few days after our late-May freeze, things really warmed up and I removed the ends to maximize ventilation. I left the plastic in place to continue protecting against cool nights, wind, and full sun for several more days. Your plants will not get rained on with the plastic in place, so be prepared to irrigate until you're ready to roll back or remove your plastic for the main growing season. |
Sunshine -- at last!
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| Here's another option I'm playing with — a raised bed made from 4" wide concrete blocks plus a rough cover of wood, plastic tacked to the back, and plain bed sheets. The tomatoes in this frame sustained less damage during our May 26 freeze, despite being less securely covered. I hypothesize that the concrete blocks retained enough heat to hold temps above freezing. (The experiment worked!) Be warned. The blocks also provide an ideal breeding environment for slugs. |
This cover system needs refinement, but it shows real promise! I'm also considering a screened version to protect against bugs and heat.
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to keep a close eye on temps. 
