The dog days of summer are dwindling and the cooler temps of September have commenced in Northeastern VT. Season extension has been a hot topic in our region as of late, and so many folks are scrambling to get ready for the impending frosts – wishing to hold on to some late season crops, and further yearning for winter greens and the like to become a near-future reality. Aside from the simplest option (row cover) to gain an extra week or two, constructing a cold frame can be an excellent way to extend the end-of-summer harvest window and can be used for sowing some winter varieties as well.
How to Choose a Design for your Cold Frame
There are many questions you will want to ask yourself first to help shape your ideas on your ideal cold frame:
- What crops do you wish to cover (i.e. low-growing greens, larger mature plants, or both)?
- What surface area will you need to cover, or what is your available space?
- Should your frame be portable or stationary?
- Do you want a long-term or temporary structure?
- Will it need to withstand winter weathering?
- Do you have recycled materials that you are wishing to use?
- What is your budget?
- What are your building skills?
- What kind of tools do you have access to?
Cold Frame Construction Options
Hay Bale Cold Frame
Hay bale cold frames are an easy option that require no building skills. They can be made to fit any size area. All you need are the appropriate number of hay bales and enough clear plastic or recycled windows* to cover the surface area of your hay bale frame, and (if you are using plastic sheeting) some logs or bricks to weight the plastic in place. They are cheap, simple, and can be put up and taken down as needed. If you plan to use clear plastic for the cover, this will work fine for spring or fall season extension, but not so well for over-wintering if you get snow. However, if you use framed glass or old windows on top this could work for overwintering as well. The hay bales provide wonderful insulation for relatively little work or cost.
PVC Hoop-style Cold Frame
PVC hoop cold frames can be easily built to house either larger, more mature plants or smaller plants, can be easily adapted to fit many desired dimensions, and are very versatile. They are fairly light-weight and are therefore easily portable – but you may want to consider staking it down so that your cold frame does not become airborne every time the wind blows. These can be built on a fairly low budget with minimal building expertise or tools. The basic tools needed are a handsaw, a heavy duty stapler, a hammer or screw gun, and a measuring tape. PVC tubing and clear plastic (recommended for outdoor use) can be found at any hardware store.
For a great example with step-by-step pictures, take a look at the Will Work for Food blog for their hoophouse-style cold frame.
Cold Frame Built with Recycled Materials
Do you have some old windows or scrap wood* hanging around that you’d like to turn into a cold frame? Depending on what you have available, you can likely fashion a very useful season-extending frame. Many of the recycled frames I have seen are on the smaller side and are best used for low-growing crops such as greens, carrots, or bunching onions for over-wintering. They can be stationary or portable, and can withstand harsh winter weather much better than a PVC hoop frame. Recycled cold frames can be made on a shoestring budget, but will require a bit more building expertise and tools such as a screw gun/drill, circular saw (or a hammer and hand saw if you are limited). With this option, your blueprint will most likely stem from the materials you have on hand, so it may take some creative thinking to turn what you have into what you need. Check out these examples for some inspiration:
- www.instructables.com has a step-by-step approach to cold frame construction (http://www.instructables.com/id/Cold-frame-construction-with-recycled-materials/) with pictures that seems pretty simple and straight-forward.
- And yet another nice cold frame design (http://www.fortheloveoflillian.com/2012/03/cold-frames.html) using recycled windows.
Custom-built Cold Frame
Custom-built frames offer the most versatile options for cold frame construction. If you have specific dimensions that you need to cater to, need a long-term, durable structure (stationary or portable), do not have recycled materials on hand, and have a larger budget, then building a custom frame may be the right fit for you. Ultimately, you will have control over what type of materials you use, and the options are a-plenty, but you may first want to determine what to use for the top window (glass, Plexiglas, or plastic), then base your building plan around that. Plywood, dimensional lumber, or tongue-and-groove construction are a couple of ideas for side walls. This option works best for a more experienced builder and requires more complex tools. I would advise against using paint, stain, or polyurethane on any of the materials used for your cold frame because these tend to off-gas for many years.
Because it’s Worth It!
We all want to taste the goodness a little earlier in the spring…and just a little longer in the fall…and why not all winter long? Cold frames are versatile, practical, and inexpensive. For the effort it takes to provide a little extra warmth and comfort for your plants, the benefits are well worth it.
*Please err on the side of caution when using old windows or other materials that may contain lead paint. I would advise that if you are unsure, do not use them. Paint jobs done before 1978 may contain lead-based paint and can pose serious health hazards, especially to young children and pregnant women. In my opinion, it is not worth taking a chance because paint chips can easily come into contact with the food that you are growing. I would also advise against using paint, stain, or polyurethane on any of the materials used for your cold frame because these tend to off-gas for many years. It is not worth exposing yourself to toxic chemicals or heavy metals for the sake of season extension, even if it means saving money.