Many people use a traditional start date for their gardens each year. For the more adventurous it could be May 1, for many it’s Mother’s Day weekend, I’ve even heard of someone who plants May 13 and when I asked what was so magical about that day he said that’s what his grandmother did but why she used that date he didn’t know.
So let’s take mid-May as a generic start date and mid-October our expected first freeze date. That’s five months, a relatively short growing season. If you could add a single month to each end of our vegetable growing season that’s a 30 percent increase of time, which you’d probably agree is a significant increase.
Semi-permanent structures like greenhouses can add much more than a month and can even be used as year-round growing areas, if you add enough heat and light sources. This is probably too much for most folks these days but an unheated greenhouse with a passive heat storage system like water barrels can add multiple months to both the start and end of our traditional growing season. However one doesn’t even need to get that complicated.
Leaving how to start plants earlier in the year for another time, extending the end of the season can be accomplished fairly easily. Everyone is probably familiar with the use of protective sheets and blankets for those early morning frosts, but these require daily covering and uncovering.
A slightly more complicated but much more effective alternative is a cold frame. The concept is simple, the application takes a little effort, but cold frames are a fantastic way to not only extend the end of the growing season but also lend assistance in starting earlier.
A cold frame is essentially a mini greenhouse; a simple box frame on the ground with the south wall lower, the north wall higher, and the sides cut at an angle to match the north and south sides which together allow the top to slope towards the sun. The top can be old windows, pieces of Plexiglas, or even transparent plastic sheets attached to a wooden frame. Hinges along the north side allow easy access and venting on days when it gets too warm inside. This simple structure not only raises the day time temperature but by heating the ground and that heat being released throughout the night the nighttime temperatures are also increased. Wind and it’s cooling effect is also reduced or eliminated by the structure’s walls and top.
Full grown plants like tomatoes and sprawling vines and melons may need more space than cold frames can provide, but cold-hardy leafy plants like spinach, lettuce, kale, some herbs, onions, and root veggies like radish and turnip are well suited for growing in cold frames. Low growing flowers can also fit well in cold frames.
If cold frames sound interesting, try one out. Start simple and small, use old wood planks and what would be throw away windows, and if you don’t have any old hinges laying around they don’t cost much new. You could even build one over existing crop rows and see the difference with and without the protection of a cold frame. Cold frames are easy ways to extend your fall harvest.
Art Smith is a co-owner of East Pierre Landscape and Garden Center, 5400 SD Hwy 34, Pierre.