Building a Cold Frame - a good idea
Have you considered building a cold frame? It's easy and very beneficial whether you want to start plants, grow summer crops or grow cold weather vegetables in the winter.
The big benefit of a cold frame is that it can be a cheap alternative to a greenhouse - a very cheap alternative. That's good news for those with an eye toward frugal living, but not enough money for a greenhouse. Let's look at some cold frames and how they might be designed to meet your interests.
Before we do, let's discuss what a cold frame is, and what it isn't.
A Cold Frame is...
At a very basic level, a cold frame is a rigid structure that allows you to cover seedlings and plants with a light transmitting material to promote growth. The idea of a cold frame is to enable the gardener to open the frame conveniently to:
- water plants
- vent and regulate heat
- expose plants to outside conditions (harden off)
- add and remove plants
The cold frame is closed to:
- capture the warm of sunlight
- protect plants from cold weather and hail
- keep drying winds off of plants
The cold frame to the left is built from wood, EMT conduit "ribs" and woven poly for a cover. The front rolls up onto a piece of EMT conduit. It also has a raised bed design.
Thanks to Jeremy and Wanda Manley for letting me explore how they go about building a cold frame, and for letting me take pictures of their designs to share with you.
If you're thinking about building a cold frame, you need to know that they can be used for:
- raising seedlings
- growing small plants to full size
- getting a head start on the season
- extending the growing season
- growing plants in the winter
Most people associate a cold frame with giving seedlings an early start, and that's a great use, but as you can see, there are so many other uses.
A Cold Frame is not...
When building a cold frame, you'll need to keep in mind natural limitations of the structure. Understanding their limitations will help you get good and proper use of what you have built.
The most important thing to remember about a cold frame is that it is not a greenhouse. This means that it isn't self-regulating with respect to temperature. If you close up the cold frame on a warm sunny day, the inside temperatures will rise quickly, and you'll bake whatever you have in there.
So, when you build a cold frame, make certain you take into consideration the need to vent out heat.
The close-up to the right shows how a small bungee cord is used to hold up the poly covering on the front after it is rolled up on the piece of EMT conduit. This allows great ventilation during the day.
Since cold frames are relatively small, it can be challenging to regulate temperature - even when you remember to do so. If you open them up, the heat rushes out in cold weather. It's a bit like a refrigerator; it doesn't take long with the door open before you've substantially altered the interior temperature.
Although they are a cheap alternative to a greenhouse, cold frames are far less forgiving and therefore, they aren't a substitute for a greenhouse.
Cold Frame Designs
Your imagination is the limit when it comes to a cold frame design. Common materials for construction are wood, metal and PVC. Common designs are square or rectangular boxes with slanted covers designed to allow in more sunlight than a horizontal cover. Other designs look more like the top of a very small covered wagon.
On the left, you can see how conduit clamps are used to secure the "ribs" of EMT conduit to the structure of the cold frame.
Here on the right is another approach to installing the "ribs" on the cold frame. Rails on the front with holes drilled through them hold the EMT conduit in place.
Building a cold frame out of EMT conduit only is also possible. Notice on the cold frame below that there are no wooden sides - just poly.
Metal semi-circle tubing holds the poly snug to the EMT conduit frame. This is a commercial product - everything else is homemade.
Don't think you have to be an expert in home improvement when you are building a cold frame. Here on the right is a hex bolt and sheet metal application that holds the EMT conduit firmly in place to the wooden sides.
Smaller cold frames can be portable and built with handles. Larger cold frames can have a permanent place in the yard. When you start to think about building a cold frame, make certain you consider whether you want it to be portable or stationary.
Some cold frames are built right on the ground, much like a row cover with a rigid framework for holding on the clear covering. You can also incorporate a cold frame into the design of a raised bed.
Still other commercial units I have seen are light frameworks that have clear sides all around. Building a cold frame yourself is a money saver, but you might also want to make use of commercial products.
Regardless of the design you choose, remember that a cold frame is small and can be tossed about by higher winds, so make certain it is secured to the ground, by weight of soil or plants, or secure it to the ground with stakes or other means.
Ways to Use a Cold Frame
Ideally, a cold frame should face south in order to pick up as much light as possible from the sun. If you're using cold frames to enhance the heat that stays around your plants, then you should position it over your plants, regardless of their orientation to the sun.
The most common use of a cold frame is to start seedlings. It helps your plants get a jump on the season, and also allows for a convenient way to harden them off.
Typically, the cold frame is opened during the middle of the day and left closed at all other times. I've incorporated seedling heating mats inside my cold frames to allow them to be placed outside even earlier than what you would in the absence of supplemental heat.
Cold frames are also used to grow plants earlier and later than the normal growing season. Cool weather crops like beets, radishes, turnips, lettuce, kale and others can be grown in relatively cold weather. You might consider building a cold frame just for this purpose.
(My apologies to flower gardeners. I don't mean to ignore you. Please understand that for me, building a cold frame or greenhouse is all about vegetables, but I do understand the interest in flowers.)
Using a cold frame, many of these cooler weather crops can be started much earlier in the season to provide an early harvest. Likewise, a cold frame can be used to grown cool weather crops much later in the season to provide a lengthy harvest.
When building a cold frame, keep in mind that it can be used to protect plants well into the winter months. As such, you will be able to harvest cold tolerant vegetables well into winter.
If you place your cold frames inside of your greenhouse or other high or low "tunnel", your gardening season need not end in many parts of the country.
The idea of building a cold frame for use inside the greenhouse during the winter would suggest that your cold frame be portable. If not, then build a cold frame inside the greenhouse so you won't struggle trying to get it in there.
Lastly, cold frames can be used to provide heat loving plants with all the heat they can handle to support superior growth. A neighbor of mine leaves cold frame covers on her peppers and egg plants all during the summer because these plants really like it hot.
Regardless of why you're building a cold frame, it's bound to provide you will lots of opportunities to make good use of it.
Happy cold frame gardening to all my frugal living friends out there that want to make the most of what gardening has to offer.
Done with Building a Cold Frame, back to Build Your Own Greenhouse