Fall in Our Vermont Trial Garden: Frost Maps and Cover Crops

-By Jay Leshinsky, NE Trial Garden Manager

It is 80 degrees in Vermont on October 9 and the student volunteers who work with me at the Middlebury College Organic Garden where we do Renee's Garden trials aren’t thinking about winter. In early October, we were still picking warm weather crops like Hot Crayon Colors zinnias, Padron and Suave peppers, Asian Trio eggplant, Italian Pesto basil, and Rattlesnake pole beans. We still have Super Bush tomatoes growing and ripening in our unheated hoop house. Then came one night of frost and our green beans, peppers, eggplant, zinnias and basil all succumbed to a white coating of ice crystals. We are still are harvesting cool weather fall crops like Catalina spinach, Pot of Gold chard, Bolero carrots and Lacinato kale, but the tops of the Bright Lights chard (planted in a different bed than our Pot of Gold chard) were frost damaged.

Hot Crayon Colors Zinnias blooming beautifully before the frost

Why were some but not all, lettuces damaged by frost? Our garden is on a hillside and there are cold spots scattered throughout were things are more vulnerable that we are gradually locating and identifying. My friend, Scout Proft, who has farmed organically in Vermont for more than 25 years (and also does seed trials for Renee’s Garden) has created frost maps for her garden. Over the years, she has purposely planted her most frost sensitive crops (basil and beans) throughout her plots so she can use them as markers to map the locations where frost occurs earliest. This way, she avoids planting fall crops that are sensitive to light frosts in those spots and is able to extend her season by planting them in her more protected, less early frost prone areas.

After the first frost, some top damage is evident

So many of the newer student volunteers see this October warm spell as an extension of summer. But the more experienced student interns who worked with me all summer have a different perspective: we have been preparing the garden for winter for over a month. Well before the average date of first frost, my focus has gradually moved from harvesting to protecting the soil over the winter from wind and rain erosion, and providing nutrients to feed the soil life that makes out garden fertile.

We have 20 different beds on our garden and rotate crops throughout the beds. Some beds are double cropped, but several are singled cropped with spring and early summer vegetables that will be finished producing by August (carrots, lettuce, spinach, beets, and bush beans). In most of those beds, we plant oats that will grow 2-3 feet in height and form a mat of green before the hard frosts of late autumn fell them. They turn brown and keep the ground covered over the winter. The oats will not regrow in the spring. We either leave the mat of brown in the bed for mulch for large transplants or rake it off the beds and compost it. These are the beds that we can plant in early spring. The texture is springy and loose.

Student interns in the oats

By early fall , we switch to cover crops of winter wheat or clover. They will get some top growth and substantial root systems before the hard frosts stop their growth. In early spring, they will turn green and start to grow quickly. We turn in the wheat or clover for a green manure crop in late spring. We put wheat and clover in the beds that won’t be planted until early June, so we can give the green matter time to decompose in the soil after we incorporate them in May. We also add compost to some of our beds based on soil testing. If we don’t cover the beds with a cover crop or compost, we cover them with straw from out wheat crop. Using this method, we’ve raised the percentage of organic matter in our soil from 1 percent to 7 percent over the past 7 years. So when signs of fall begin and summer crops slow down their production, I tell the students that it is not the end, but the beginning. It is time for them to do the essential work of protecting and improving the soil for next year’s garden.

Jay spreads a straw cover on the empty beds