There is a morning every fall when the vegetable gardener grabs his/her coffee/tea and heads out into the garden. The harvest is starting to slow up and there is an extra bite of chill in the air. Soon, a white blanket of frost will cover your beds. For some gardeners, it marks the end of the year. For stubborn gardeners like myself, we want fresh, pesticide-free veggies from the backyard, and as few produce as possible from Mexico or New Zealand or Russia where fuels are consumed to haul them thousands of miles to the local grocer. We’re not localvore zealots, but if possible, we want to keep veggies growing until a really hard freeze.
This year, I had to face frost for the first time in over a dozen years. I wanted to build a frost blanket system that I could not only use for short veggies, like lettuce, but also for taller plants like broccoli and cabbages. Next year I will use the same system for a shade cloth to protect veggies from our scorching sun.
Here’s what I came up with:
Frost blanket framing using PVC pipes
A Quick Math Primer
We will use the forumula > 2∏r < (the circumference of a circle, where ∏=3.14) to determine how much PVC pipe to make a semi-circle over a row. This is just to get started because your semi-circle may be more semi-elliptical to account for taller plants. Let’s simplify ∏ as the number 3.
Therefore, a half circle is 3 times 1/2 the width (i.e. diameter) of your bed, or even simpler, 1.5 x width of the bed. For the above bed where the width is 4ft, the minimum pipe length should be 6 ft (1.5 x 4).
Half inch PVC pipe fits well over rebar
Use a half inch coupler to join PVC pipes.
Low, Med, High, Super High
By using inexpensive half inch couplers, you can adjust the height of this frost blanket system to match the height of the vegetables you are protecting. Remember that you want the blanket to get as close and low to the vegetables as possible without touching them. It’s the warm air pocket that insulates the plants, not the blanket.
My Frost Blanket System
- Purchased 10ft x 1/2″ PVC pipe. Easy to bend and cut. Made two lengths of 18in sections off each pipe to use as extensions.
- Also bought 1/2″ PVC connectors to put on one end of the pipes. Allows to change the height of the system.
- 3/8″ rebar in 1ft sections, but you may want 18″ or 2ft if you have soft ground.
- Remay cloth for the frost blanket. It is 67″ and you can buy different lengths. If you need a tall cover, you may need to double the frost blanket as the standard width is 67″ (5ft 7 in.)
Use Remay cloth for frost protection.
Rocks hold down Remay cloth. Clips or old garden hose segments fasten to PVC pipe.
Other Frost Management Tips
- Water often (avoiding the leaves) and well. Water is your veggies’ defense against frost. Keep the ground moist.
- If you can water with warm water from a garden hose that is out in the sun or if you have a small bed of fall veggies, water with warm water at night before you go to bed.
- Mulch with hay or newspaper around vegetables to keep soil warm.
- Don’t forget to remove the blanket if you have a warm day.
- Instead of using expensive clips to attach the Remay, you could take an old garden hose. Cut 2-3″ lengths and make a slit down the middle so it can go around the PVC pipe.
Remay clips can be bought or made from old garden hose sections slit in half
How awesome. Every year I say I’m going to plan a fall garden, but I don’t. I don’t know what we’d do without a local farmer’s market. Thanks for the tips, I’ll keep them in mind for next year!
[...] This post was mentioned on Twitter by Plangarden, Plangarden and Sean Wilson, Mary Welsh. Mary Welsh said: RT @plangarden: Finally got our blog done of Frost Blankets http://bit.ly/bqaWO0 This is how I intent to extend our gardening season. [...]
Thanks for the garden hose clip tip. What a great idea and I always have plenty of hose that splits over the winter.
Great post! Love the hose tip!
Great tips on frost management, I like the idea of mulching but I sometimes think I won’t be able to find the slugs in amongst it.
I like your idea of recycling the old hosepipe for clips. I’ve always used the metal pegs in the past to keep the fleece secure in the soil but they leave large holes if you need to move their position which allows the pests to get through, the hosepipe clips look much better.
Great post and pics! I’m wondering, though, how warm is so warm that the frost blanket should be removed?
Depending on what type of ‘heat’ you get and how much your plants need/want to be warmed. Example: If it is warm and no wind, then it can get toasty under the frost blanket. The frost blanket can raise the temp under it 5-15 degrees (again depending on sun and wind). So if it is getting into the mid 70s, you may want to move the clips up to let a breeze blow through the tunnel.
I bought the expensive clips just to see if they were better than my hose clip idea. Now that I see them in action the expensive clips hold better. Almost too good. (The expensive clips are move likely to lead to tears in the Remay cloth.) The hose clips are gentler on the cloth. The hose clips don’t grip as good, but since I have 20ft of bad hose, I can afford to add as many as I want, and they don’t look hideous either
I use iron phosphate for slugs. Sluggo is a brand of slug killer that uses that. Iron phosphate is deadly to slugs, but breaks down into organic fertilizer. But you are right that slugs may hang out in damp hay.
you should check out some of Eliot Coleman’s stuff. He is an expert when it comes to growing stuff in the cold.
here are some tips:
Don’t water when you expect a hard freeze. the extra moisture will cause the plant cells to burst.
use more pvc pipe to make clips. If you use 1/2 pvc use 3/4 to make clips. cut the 3/4 into 1 inch sections and then cut it almost in half. this will make a nice tight fitting clip. Don’t forget to file the sharp edges down though.
check out my video for a quick visual.
I was stubborn last year and kept plants going to Thanksgiving, in spite of temps in the mid 20s at night. I didn’t have much of a set-up, just a heavy duty frost blanket and I just threw it over the plants and used earth staples to keep it from blowing away. On the coldest nights, I tented some cardboard boxes over some plants.
But we already had our first hard freeze two weeks ago. This year, I just didn’t get around to getting any plants in in time for them to get going. So it’s indoor gardening for me this winter.
I’ve used a tunnel row cover made of a double layer of clear poly for many years to successfully grow spinach, lettuce, and onions through winter here in the midwest, with temps well below freezing. Wire hoops are integrated into the poly every two feet, with about 6-8 inches of wire to stick into the soil on either side. The 16 ft. long tunnel was less than $20 on sale.
Love your coldframe and I agree that your PVC clips hold tighter than hose. The PVC is a good idea if you can or don’t mind buying the extra pipe and the extra work. You will get better holding power. In my case I had an old hose and don’t mind the fact they aren’t as solid fitting. I am using them in the center poles now and the expensive clips on the ends.
As for not watering during a hard freeze, I think I disagree with Eliot on this point. His argument is bases on the fact that the part of the plant that is not water (80-95% of the plant is water) has a lower freeze temp than water. But the water is there to keep the soil warm (warmer than freezing) The combination of water in the ground and cover over top is what protects you from freezing. I watched one of Eliot’s teaser videos on YouTube. In the video he mentions how the water condensing on the top of the greenhouse cover creates a prism effect to help warm the greenhouse during the day. It takes a bit of water to do this, so I think he is keeping his ground saturated too.
Water will do more good than harm. I think it is dangerous to find a watering level that warms the ground and allows condensation on the top of green house, yet keep the water in the plant at a lower concentration. 9 times out of ten you will do better watering. If you want an extra bonus for a hard freeze, I would let a hose sit with water inside during the day and absorb solar energy (what it can) and water in the mid to late afternoon. Every extra calorie of energy that you can try to store in the ground will help. And with a really hard freeze, there is not much that can save your veggies.