Ask a Master Gardener

Extending the Growing Season with Cold Frames

10/5/24

Here we are in October. How did that happen? Wasn’t it just a few days ago we were melting in the heat?

This is the time of year gardeners start thinking about that first freeze of the fall season. The average first freeze date is typically around Nov 15th, but the last couple of years our first freeze has been earlier. Last year our first freeze was on October 30th but the year before it was October 18th. All this to say, that first freeze of the season could be right around the corner.

Why do gardeners care about that first freeze date? Because it will put an end to many or our summer vegetables like tomatoes etc.

If you aren’t ready to call it quits in the garden any time soon, you can utilize what is called a cold frame to extend not only your fall growing season.

Cold frames are kind of like a mini greenhouse. They can typically be built from scrap wood. We’ve even seen old house windows serving as a top for a cold farm. Or you can also build them out of hay bales and a slanted window to let the sun in. One of the good things about using straw or hay bales is that it would be a temporary structure, something you can use in the winter but then take apart in the spring.

The great thing about a cold frame is that temperatures are usually 5 to 10 degrees warmer inside the enclosure than outside, which means you can continue to grow inside the cold frame for quite some time. And if it gets really cold at night, you can throw a blanket over the cold frame to keep your veggies safe,

There are a bunch of different ways to construct a cold frame but for the most part they are rectangular boxes with a transparent roof. When building your cold frame, plan on placing it running east and west so that it will get good southern exposure for that warming sun. Also, plan on having the lid of the cold frame be on a slant to allow for drainage and more exposure to the sun. On warm days you may need to open up the top so that it doesn’t get too hot inside. A little bit of weather stripping isn’t a bad idea either for colder days.

Oftentimes cold frames get utilized by those who love their home-grown salads, and a cold frame will let you be able to enjoy those greens a little longer in the season. Then in the spring, you’ll be able to start growing earlier in the season due to your small, sun-warmed, mini-greenhouse. Good luck!

You can get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th Street, or by emailing us at mg@tulsamastergardeners.org. Photo: iStock Photo