Fall temps can quite literally cool our northern garden jets once September hits its stride and apple season arrives. But for those of us that enjoy those frost sweetened crops and don’t mind gardening into the cool of autumn, Season Extension opens another mini-season of gardening and harvesting!
For those just getting started on season extension, you may be wondering why we bother with this extra work?
For me the reason is that by keeping plants alive in the ground, it allows them to hold onto their nutrients, compared to if we harvested at the first sign of frost. Food loses around 30% of its nutrients within three days of harvest.
Practicing season extension can add weeks or even months of harvesting FRESH FOOD from your garden. And isn’t harvesting healthy food one of our main goals?
*This post includes some links to products I have tested, and as an Amazon Associate I earn from qualifying purchases.*
Season Extension Factors
Successfully extending the harvesting season depends on a few individual factors. Each one affecting the other; like the plant variety, weather, your growing zone, microclimates within your garden and if deciduous trees drop leaves and add a little more sunlight to an area that is shady during the summer months. But it all starts with the right plants!
Knowing which plants do well in cool weather is key to success. We’ve got a list of the 21 most common garden plants (everything from Arugula to Zucchini) and their germination temps and their low temperature threshold listed on page 46 of our book, Small-Scale Homesteading. You can also find most of this information online at whichever seed company you purchased your seeds from as well. Johnny’s Seeds and High Mowing are especially good at adding this info online. It can be surprising how much low temp threshold variation there can be between what we all typically think of as cool weather crops. So do your research and you’ll be ahead of the game!
Growing Under Coverage
The next key to success is adding some physical cover over the plants. There are many ways to add a layer of protection over your plants, from simply setting a plastic bin over a few plants, or quick to set up and moveable low tunnels, to permanent cold frame structures. Even adding a layer of dry, shredded leaves will help protect many root crops for a few more weeks.
We pop up these kinds of covers for two different reasons.
- To protect frost sensitive plants
- To hold cold-hardy plants in the garden longer
The first category of plants we cover up tend to be lettuce and other plants like broccoli and cauliflower that can typically handle down to 28F without damage. So, if we know a frost is coming, we’ll get the cover structure up *at least* a day or two before the temps dip. This allows the soil and air temps to gain a few degrees before they get to the critical low temperature.
Managing the temperatures inside low tunnels and cold frames is a bit of an art. The air temps under coverage will vary greatly depending on how sunny the days are. Even with air temps in the 20F’s outside, we’ve had air temps inside low tunnels above 70F (this happens both in the spring and the fall).
Temperature Fluctuations
The thing to watch in adding a low tunnel to plants in the fall is that the sun still drastically warms the air. Sudden changes can cause plants stress because they have to quickly change up their internal metabolic processes. Even experiencing this one time can lead to a weakening of the plant’s overall vigor. This in turn makes it more susceptible to diseases and pests. If we’re using this practice at the end of the season for an annual plant, this weakening isn’t crucial for longevity. It is good to know both for spring low tunnel use – and because drastic air temperature fluctuations will affect the quality of produce you harvest.
Depending on when the sun hits the low tunnel (or cold frame) temps can easily rise 10F every half an hour. And this is where plants can suffer from temperature shock.
In a typical Minnesota fall, temps can be down in the low 40’s overnight and back up to the 70’s in the afternoon- so it doesn’t make sense to say there’s a specific number of degrees plants can handle in a day. The issue is that under a plastic cover the temps increase more rapidly than in a natural setting, so the plants don’t have time to adjust their internal processes.
Opening up the end of the low tunnel in the morning, and closing back down early in the afternoon to keep temperatures as close to 50F is typically my goal.
DIY Low Tunnel
Low Tunnels are easy to construct and move around to follow your crop rotations. Start by pounding in 2-foot lengths of rebar at your corners and along the edges every 2’ or so. Then slide some ½” PVC over the rebar. This creates an arch over the bed when you slide the PVC onto the rebar on the other side of the bed. Then add a stick of PVC the length of the bed. At the top of and perpendicular to the arches, to add strength to the structure. You can easily secure with zip ties.
Cover in plastic between 2-6 millimeters thick. Cut so you have enough to make good contact with the soil all the way around. You can use a longer piece of rebar or rocks, lumber etc… to weigh down the edges. Secure the plastic to the PVC with clips or clamps. This whole set up can cost as little as $40 and will last for years.
Know that you’ll be peeking in to check on temps often, so adding a soil thermometer and a regular small exterior thermometer where you can easily see it makes that step lots easier.
If you’re looking for an easy all in one option? I know garden friends who enjoy this combo of a structure and easily to install 3-Season Plant Protection Tent from Gardener’s Supply. (I am not affiliated with them).
Season Extension has added months of fresh harvests for my family over the years, and I hope it can do the same for you!
What questions do you still have about starting this process?
Let’s Dig In!
Michelle
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