Veggie Garden 101: Frost Protection

Low tunnel with Tufflite plastic and Agribon-19 row cover.
Photo: Liz Bosak.

When nighttime temperatures dip towards 32 degrees Fahrenheit, many vegetable plants benefit from some frost protection. Commercial row cover fabrics, such as Agribon 19, provide about 2-3 degrees of frost protection. Heavier weight row cover can provide closer to 5 degrees Fahrenheit. In general, the heavier the fabric means less light penetration. Adding a layer of greenhouse plastic adds at least 9 degrees. If you don't have a commercial row cover fabric, you can use a old sheet for the night and remove in the morning.

Low tunnel with Agribon -19 row cover. Photo: Liz Bosak.

The trickiest part of effectively covering plant rows is supporting the cover above the plants if possible and securing the cover. Sandbags filled with sand, gravel, or soil work well. The row cover pegs only work well in loose, deeply tilled soil or in sandy soil. Shovel fulls of soil placed on the edge of the row cover takes time but it's free.
What to watch out for: 1. if the daytime temperatures go above 60 degrees, it is best to remove the row cover fabric.2. if using row cover + plastic, remove both layers during the day if temperature exceeds 60 F. These recommendations are for cool weather loving crops such as spinach, lettuce, broccoli, kale, mustard greens, arugula, and peas.
Supporting the row cover with wire, galvanized steel, or pvc/plastic hoops prevents the frost from significantly damaging the plants where the leaves touch the frosty row cover at night.

Variety Recommendations: Hail the Kale

Why kale?

Kale is a green, leafy vegetable in the Brassica or cabbage family. Most preparations of kale are similar to collards. In my experience, kale is easy to grow and withstands extremes of soil moisture and air temperatures. It is one of the last vegetables to succumb to freezing weather when it is unprotected and is a robust addition to unheated low tunnels for winter and early spring harvests. Kale in its seedling stage is an excellent green to add to salads and keeps well in a salad mix when properly harvested and stored.

My favorite varieties of kale include 'Red Russian', 'Beedy's Camden', and 'Nero di Tuscano'. All three varieties sailed through the polar vortex winter of 2014 in an unheated low tunnel. I had seeded very heavily for salad greens and braising mixes at the early spring harvest timing. The spring of 2014 harvest was two weeks late compared to 2012 and 2013. After the spring harvests, I removed the 'Nero di Tuscano', for whatever reason, it was not as vigorous. I thinned the 'Red Russian' and 'Beedy's Camden' and harvests continued through the summer and until a killing frost in November. Many suppliers offer 'Red Russian' and 'Nero di Tuscano' but I have only found 'Beedy's Camden' from Fedco Seeds.

Planting the seeds of a low tunnel revolution

Last month, a group of volunteers helped to set-up a pilot low tunnel for the Gardening for Good project at Troy Community Gardens. Gardening for Good is a supported gardening project that hosts regular activities and special events to bring gardening to people with developmental disabilities. To learn more about Gardening for Good, go here.

I had a tremendous amount of fun sharing what I had learned after just two years of winter growing with unheated low tunnels. The summer gardening season is starting to wind down and I hope to have a little more time this winter to share some stories and ideas about extending the season in Wisconsin.