Eco-Saturday: Bubble-wrap cold frames

This is an easy garden project for a Saturday afternoon.

You will need:

Cinderblocks
Mulch cloth (optional)
Topsoil, compost, peat moss or some combination of the above
A few bricks or rocks
Scissors
Duct tape
Heavy-duty bubble wrap (the kind with the big bubbles)

If using mulch cloth, lay it down over the area where you plan to put your raised bed. I have mixed feelings about mulch cloth. It helps with weed control for a while, but it gets in the way when I’m trying to plant seedlings. I skipped it this time.

bubble1

1. Arrange your cinderblocks to form a bed. I’d recommend designing a rectangular bed, as it will be easier to work with when you create the bubble-wrap blanket for the top. Mine is circular because I planted last year’s garden in a pre-existing fire pit in the backyard, and I didn’t feel like rearranging the blocks. The smaller the bed, the more thermal mass you’ll have for keeping plants warm, so keep that in mind.

bubble2

2. Fill the bed with a couple of inches of planting medium (topsoil, compost, peat moss, whatever).

bubble3

3. Plant whatever cool-weather seeds you feel like growing and water them. I used a lettuce mix I found at the Co-op, but spinach, kale, radishes and some herbs are also good choices.

bubble4

4. Lay strips of bubble wrap, bubble side down, across the top of the bed. Duct-tape the strips together as neatly as possible. For a rectangular bed, you can measure your dimensions and do this step inside on a flat surface, which I’d recommend. Leave enough excess around the edges to be sure all the soil is covered and to have room to weigh down the bubble wrap when you’re done.

bubble5
5. Lay bricks or rocks around the edges to keep the bubble wrap from blowing away. Trim the edges to make them look neat if you want.

Cold frames work like little greenhouses: The transparent plastic lets in light and traps heat, warming the soil. Cinderblock walls add thermal mass, and bubble wrap provides extra insulation, allowing you to start planting even earlier.

Happy gardening!

Emily

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18 thoughts on “Eco-Saturday: Bubble-wrap cold frames”

  1. Umm…great idea, but you did not leave any room for plants to grow taller than a few inches under that bubble wrap…and if you should get a sudden heavy rain or snow fall, that will crush the plants from the top as well.

    What about just making a 2ft tall wood frame (surrounded w/gopher wire to protect plants from hungry critters), and just put bubble wrap around the sides and top of that? You could even leave an inch of ventilation at the top of the sides so plants do not over heat on a warmer winter day. Just sayin.

    1. Your design would probably stand in nicely for floating row covers, but I’m not sure it would serve quite the same purpose as this cold frame, which is designed to germinate seeds a few weeks ahead of schedule. With wood and wire, you lose the thermal mass provided by the cinderblocks. This was tall enough to give my arugula a head start, which was all I really needed it to do. If this were a rectangular bed, and if I didn’t have perennials growing in some of the holes around the perimeter, I’d just stack a second layer of cinderblocks on top of the first, as I did with the brick-and-plastic-sheeting cold frames I had when we lived in Belleville. This bed is a fire pit I reclaimed when I moved in — hence the awkward shape and size. I’ve basically used it as a test plot the past two seasons as I figured out the quirks of a new yard. The bubble wrap worked well enough that I’m planning to build two-block-high rectangular beds this winter in the area my quail have prepped for me along the east fence and staple the plastic to wooden frames on top to make a more durable cover. You are correct in assuming the plants might need ventilation on unusually warm days, but a cold frame is basically a passive solar heater. Because passive solar relies on trapping heat, you want to limit ventilation to those times when it is absolutely necessary — which is accomplished easily enough by pulling back the covers on warm mornings and tucking the plants back in at night.

      I didn’t have any problems with rain or snow crushing my plants, but I can confirm that bubble wrap was not engineered to support the weight (or toenails) of a collie mix with more enthusiasm than brain. o_O

  2. Yes, it depends on what you wanted to use it for…starting seedlings ahead of time will work nicely for that lower design. I built six 12″ high raised (square) beds out of two inch thick untreated cedar. Then I built “removable” frames (2ft tall) that sit secured directly on top of the raised beds. I used gopher wire over the sides and tops of those frames due to the variety of critters that would love to eat my plants…gophers, birds, deer, coons ect. I followed that with bubble wrap (the large heavy duty industrial kind) as my first attempt to baby plants through winter…having no power in the back acre. This project is important to me as I am growing medicinal plants that take two full years before a fall root harvest.

    These plants normally go dormant when temps are around 35 degrees or lower…also when it gets too hot (around 90ish or above), so I am attempting to thwart that and see if I can get more growing time in before temps plummet. It is kind of awkward right now, because day time temps are still warmer (75-80 degrees) whilst night is dipping to 40 now…I don’t want to cook the seedlings. Right now, I can see the little seedlings just beginning to sprout. It is starting to get cold at night, so the bubble wrap will go on top rather than just up the sides as they are at the moment.

    Do you think I should wrap the wood part of the raised beds too…or do you think the thick wood will work by itself as far as keeping the soil warmer?

    We get about 5″ of snow from time to time during winter, so I built the frame tops to be able to handle that load…they should withstand wind as well as the smarter animals that might try to remove them. Otherwise, I am hoping this will work out as I have read that bubble wrap can give an extra zone of warmth.

    As for hot summer, I will replace the bubble wrap and use shade cloth when that time comes.

    BTW, thanks for sharing! I feel that I may be on the right track for a newbie.

    1. Once you get them started, most herbs will tolerate just about anything except wet feet, although some of the tropical species obviously will be fussier. Your raised beds should be fine without extra insulation, as the soil will provide some thermal mass on its own.

      What are you growing, and where are you located?

  3. Looking at your pics, do I see dandelions growing around the outside of your fire pit?? Those are what I planted as medicinal plants. 🙂

    Here in the mountains, no one can grow them because of the copious amount of pine/cedar trees. We had to buy over $1200 worth of organic compost and soil amendments just to grow “weeds” ! Haha!

    Sheesh.

    1. We’ve got dandelions everywhere. Do the evergreens put out chemicals that kill other plants, the way black walnut trees do, or is it simply an issue of too much shade? I didn’t think anything could kill a dandelion, except maybe a direct hit from a kettle of boiling water. (And even then, they come back with a vengeance.)

  4. Yes, the evergreens sap all over the place and also thick pollen twice a year which makes the soil very acidic, or maybe the soil is already acidic which is why these kind of trees grow here so well in the first place…AND they are constantly dropping needles all year round. Tree shade is rarely the issue with dandelions since it is filtered anyway unlike a building would be. I think the other thing is a water issue. Most areas up here are not landscaped (a la natural) especially with lawns because of all the constant and various tree droppings, unless it is a cultivated garden with drip system. Golf courses, school yards and parks are sprayed poisons to kill weeds (which means dandelions too).

    If a dandelion should “make it”, the gophers, deer and birds will eat it straight away upon sighting. I have seen them growing briefly along roads, but they are contaminated by traffic exhaust.

    Dandelion root has cured/controlled many different kinds of cancer…especially advanced Leukemia, prostate and breast cancer if used before a person submits to chemo/radiation/stem cell transplants. Otherwise, it becomes a crap shoot due to a crashed immunity system due to conventional treatments. However, the “organic” stuff you can buy at health food stores or online are really worthless because they come from Croatia and sit around in warehouses for Lord knows how long before someone orders it to stock their shelves. Even then, the roots are cut up before drying which oozes out all the medicine, and then to top that off, they pasteurize (high heat) for longer shelf life …even moth and bugs wont eat it then. Heat over 100 degrees degrades the medicine/vitamins/minerals in the root and the shelf life is only one year even without that. So people need to grow their own or get it from unadulterated land.

    1. Also — something I’m trying for next season: The feed store up the road sells metal fire rings that are about 3 feet wide and a foot and a half tall. I’ve taken to buying one every paycheck, and a friend of mine has horses, so the plan is to spend the winter filling fire rings with horse manure and dead leaves. I’ll fill one, then turn it into the next, and keep going like that all winter, so by spring, I should have a garden full of raised beds filled with finished compost to grow my tomatoes in next summer — kind of a variant of square-foot or French intensive gardening. We’ll see how it goes.

  5. You may be onto something I had not considered regarding the wood ash. We burn wood for heat and my husband just dumps the ash along the side of our property (so now I will get a metal barrel and tell him to put it in that instead). We also have lots of oak tree leaves each fall, so I can rake them up and make a proportioned “mix” all winter long to add to the native acidic soil…then do a soil test later when it looks like it might be “ready”.

    We are stuck doing raised beds regardless because of the wild life and not having any fences. But I do not mind that since once they are built, they will last for years especially the way we did it. I need to build 6 more before winter, but my son (who is the one who always does the grueling stuff around here) is now studying to pass a State Exam for the next six weeks…which means I have to leave him alone.

    What is the metal that the fire rings are made from? (Never seen/heard or of them). We have a feed store not too far from here, and if I knew what they are primarily used for then I can look into that idea. Are they round? (Rings are usually round haha).

    I buy compost because we have only been in our house for a little over year…and I have been way too busy putting that reconstruction project together to start a composting bin as much as I wanted to. I use “Happy Frog”, “Ocean Forest”, vermiculite, peat moss, worm castings and bat guano as my mix (recommended by the Author of the square foot garden). I did not use our native soil this time around because I wanted to get this started asap…and because that would mean digging in rock hard earth…I do not have the strength/energy to do that and husband is simply not interested. You have inspired me to save all the dead leaves instead of hauling them to the dump…thanks!

    There are two graves in the back of our property, unmarked except for the stones that surround them, and one is too large to simply be a family pet…definitely human adult size. I wanted to have the property graded back there for more garden room because that is where the most sun is, but am afraid that those graves might be shallow. :0 Behind us is BLM land that “belongs” to the forest so who knows what this development was occupied with in years gone by. There are Native Indians who once lived all around here until the 1800 Gold Rush. Those graves are typical of the way they would bury their dead…very simple and surrounded with rocks.

    1. You’re definitely better off making compost than buying it. If you keep the pile relatively small (like no more than, say, 5x5x5), you can get it to heat up quickly with about 10 minutes’ worth of maintenance a day, and if the weather isn’t too wet or too dry, you probably can get away with turning it every other day and still keep the thermophilic bacteria thriving. I’ve always found turning compost to be weirdly therapeutic, and it’s especially satisfying to turn over a forkful of compost in the middle of winter and watch steam rise off because the bacteria are doing their jobs. I’ve got a basic compost recipe here. The big key is just to keep roughly equal amounts of “green” (nitrogen-heavy) and “brown” (carbon-heavy) ingredients, turn it every couple of days to aerate it, and hose it down as you aerate if you haven’t had a good rain that day. In your case, I’d use manure for the greens and start with a 50/50 mix of leaves and wood ash for the browns and see how it goes. That should help raise the pH of your garden soil. If you don’t have time for composting right now, you could also try sprinkling a layer of ash on top of a dormant bed. Lye, which is about the most alkaline substance you can find, is made by percolating water through wood ashes, so it stands to reason a layer of ash sprinkled over the soil would raise the pH.

      I was about to recommend lime to raise the pH, but as I was double-checking something, I ran across this article, which might help you sort out your soil-chemistry issues a bit better. Probably the best thing to do is call your local extension service and ask them for a soil test and some recommendations.

      The fire rings I put in my garden are made of galvanized metal. Here’s a link to the kind I have. They usually run about $40 apiece, but you may be able to find them cheaper if you keep an eye out for sales. They make bigger sizes, too, but my garden is small, and I prefer a smaller bed so it’s easier to tend.

      1. Oh, and don’t let anybody charge you good money for worm castings. Vermicomposting is SO easy and low-maintenance, there is absolutely no reason to hire it done. When we lived in an apartment, I kept a worm bin in a plastic shoebox under the sink and used the castings to feed the culinary herbs on my balcony. I haven’t set up a vermicomposting bin since we moved, but I’ll probably put one in the basement this fall. Eventually, I’d like to build rabbit hutches in the backyard and put a worm bin underneath to compost the droppings, but Ron is staunchly opposed to this idea — a position I’m sure he will maintain riiiiiight up until he comes home from work to find me slow-roasting one of the little bastards with garlic and rosemary. XD

  6. Oh yes, I have seen those galvanized “feed troughs” over at the feed store. I had originally thought to just buy a bunch of them for raised garden beds…then thought that having a metal bottom could present a problem even if a lower drain plug were present. Then I thought to just drill plenty of holes in the bottom of them, then put gopher wire under them (for obvious reasons)…then I thought that maybe the metal would “leach” something into the soil over time and “corrupt” my grows. I must be overthinking because I chickened out and made mine out of untreated cedar instead. I will look into this again and check out facts to see if galvanized steel can present a problem as far as leaching anything into the soil before deciding.

    THANKYOU so much for the illustrated simplified composting recipe!!! The way you explain it takes all of the mystery out of it. I imagine you get lots of earth worms too? I had even had a flash of having my own worm farm after seeing many on Youtube.

    OMGosh…a neighbor right down the lane from me has HORSES! Horses poop…which means that MAYBE they would like to part with some of it. I am assuming that the horse manure would qualify as the green part of compost? Then to that a 50/50 mix of wood ash and leaves? Or maybe 25% horse manure, 25% green kitchen scraps and then the combo of wood ash/leaves for the rest of it? I want to use kitchen scraps too…especially during the summer when we live off a TON more of fruit and veggies.

    Another neighbor has chickens…would that work too if I strike out with the horse manure? As for other types of kitchen scraps …I throw them over the deck for the raccoons, black bears and mountain lions…they always disappear. Actually, I have been throwing ALL kitchen scraps over the deck but now I will use the fruits/veggies for compost from now on.

    Gunna get me a pitch fork pronto…

    When the compost is hot and steaming, does that mean it is usable at that point? Do you then mix it with dirt?

    Can you tell that I am brand new to all of this?

    1. You want the fire rings, not the feed troughs. The fire ring is just a ring. The trough has a bottom. You don’t want something with a bottom; it will just waterlog your plants and rust out.

      As for your compost: You’re overthinking this. We’re talking about a compost pile, not a toddler. As long as it gets a relatively balanced diet, it won’t care what you feed it. I promise. The best thing to use in a compost pile is whatever you can put your hands on for free.

      To build a compost pile:

      Put down a layer of greens (manure, grass clippings, kitchen scraps, whatever).
      Put down a layer of browns (dead leaves, straw, hay, sawdust, ashes, whatever).
      Hose it down.
      Repeat until you run out of materials.
      Aerate the pile every day or two by using the pitchfork to turn it completely upside-down, one forkful of material at a time. Hose it down between layers if it seems too dry. You want it about as wet as a wrung-out washcloth.

      If it’s balanced right and has an appropriate moisture level, it will start to heat up within a few days. Heat in the middle means it’s working. Keep flipping the pile upside down every day or two until it turns into dirt. You’ll know it’s ready when it stops steaming and you don’t see any recognizable objects in there (turds, vegetables, whatever). If it stops steaming before it turns into dirt, something is out of balance. If it smells nasty, you’ve probably got too much nitrogen. Add some browns. If it’s wet and smells nasty, it’s probably gone anaerobic. Turn it a couple of times a day without adding any water until it heats back up and stops stinking. If everything seems OK, but the weather has gotten ridiculously cold, it’s probably just dormant. Either throw a dark-colored tarp over it to thaw it out, or just leave it alone until the weather improves.

      Some people mix finished compost into the soil, but I see no point in this. Finished compost won’t hurt your plants, so I just use it as mulch or throw it in my raised beds to fill them up.

      Your compost pile truly doesn’t care what kind of greens or browns you use; it just wants roughly equal amounts of each. I suggested adding some wood ash to help bring down the acidity, but I wouldn’t get too wound up about it. My reclaimed fire pit was nothing but three inches of ash when I started planting stuff in it last year, and it worked just fine. I added peat last winter just to fill it up. The plants didn’t care. If you’re having problems with excess acid, you probably shouldn’t use pine needles as your carbon source, but beyond that, it really isn’t important.

      Galvanized metal will probably leach some iron into the soil, which won’t hurt you or your plants.

  7. Why is Ron opposed to rabbits? Is he scared of them hahaha! I would like chickens, there is nothing like fresh chicken and eggs. Did you know that stores sell eggs that are up to a YEAR old? Even the “organic” ones! We have a neighbor that has chickens and sometimes sells eggs…they leave them out front with a box to deposit money in. But I want MY OWN. I have a friend who has had chickens for decades (she only eats the eggs, but not her chickens). Even when she lived in town she’d find a way to keep chickens. Rabbits are good eating too…and well, their fur is rather soft…a rival to my other furs that I have inherited (but never seem to wear…yet). Does being vegetarian mean that your sensibilities would prevent you from eating meat…ever? Do you enjoy RAW milk? We do…and make out own butter, raw yogurt and quark too.

    1. Ron doesn’t want rabbits because they’re a pain in the arse. We had chickens when we lived in Tulsa, but our current town has a city ordinance prohibiting residents from keeping chickens in town — hence the quail, which for whatever reason are not mentioned in the long list of Birds You Are Not Allowed to Have.

      I’m not vegetarian, but I try to work a vegan meal or two into our diet every week, and having the Vegan Friday feature keeps me from slacking too much or making the same thing all the time. I refer to myself as a vegetarian sympathizer: I’m not always on the wagon, but I’m always willing to help somebody who is (or wants to be).

      If you get chickens, I recommend a portable coop, sometimes referred to as a “chicken tractor.” You get all the advantages of free-ranging the birds without any of the drawbacks. The birds are safe from predators and sheltered from the weather, but they’re still outdoors in relatively natural surroundings and have fresh forage every day. If you look under “backyard chickens” in the categories on my blog, you’ll probably find a bunch of pictures and references to our old flock.

  8. Hmm…every day I see quail and birds eating off our back yard. They must be finding something worth hanging around for because they are there a lot. So I could let my chickens range around during the day to eat whatever those birds are eating…then put them away for the evening. But it gets so cold here. I would have to give the right kind of shelter some thought…also gets hot, but we have lots and lots of trees. Then there are the animals who would like to eat them, so I would have to protect them regarding that too.

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