News Archive 2009-2018

Season Extension at Bowdoin Archives


Mike Perisho admiring a fine crop of mustards

We at the Bowdoin Organic Garden are faced with several challenges. We are committed to providing our dining facilities with as much quality produce as possible, utilizing approved organic practices. Not only are we currently operating on a modest-sized piece of land (approximately half an acre), but we also have a fairly short growing season here in Maine.

According to the USDA, Brunswick, ME has an average growing season of 153 days per year, based on the last day of frost in the springtime and the first killing frost in autumn. This compares to 166 days in central Connecticut, or a scant 92 days in Fort Kent, 5 hours to the north. The latter serves as a reminder that we actually have it pretty good! Nonetheless, our ambitions require that we move quickly as soon as the ground is workable. By focusing on improving soil fertility and planting intensively we are able to achieve fairly generous yields. Still, we look at other options to increase production.

Here’s where season extension enters the picture. Fortunately we have an authority on that subject right here in the State of Maine. Eliot Coleman has been growing vegetables in Cape Rosier, Maine since the 1970’s. He is widely considered a pioneer in organic production, inventing and refining tools, and perfecting cultural practices on his farm. Early on he became eager to learn how to grow salad-quality vegetables during the times of the year considered impossible by most farmers. By studying systems used since the 1800’s in France and England he discovered secrets to season extension that were almost forgotten. Being highly observant and a meticulous record-keeper, Eliot has experimented with different techniques, and has been able to harvest vegetables throughout the winter for the past several decades. Anyone who recalls the winter we had last year should know what a feat this is!

There are many revolutionary ideas explored in his book, The Winter Harvest Handbook. If you’re at all interested in eating fresh, homegrown greens year-round consider giving this a read.

dew cover

Evidence of row cover fabric protecting the crop from dew and frost

Many people who walk past our gardens look perplexed by the yards of stark white fabric, billowing in the breeze, covering many of our beds. This row cover has many uses, especially in organic production, and is a product that has been widely used by the likes of Eliot Coleman and growing numbers of farmers throughout New England. In the summertime it is most helpful in excluding the many insect pests that would otherwise love to reside in our crops. Critters like flea beetles, cabbage moths, potato beetles, and aphids can be fended off. Row cover also acts like a mini greenhouse, a characteristic that lends itself to season extension. The majority of sunlight is able to pass through the fabric. Much of the reflected light or heat trying to escape simply gets reflected back within the fabric’s protective shelter. This allows the temperatures within to be significantly greater than those of the ambient air, and leads to less temperature fluctuation. The fabric itself also keeps humidity off the plants underneath it, which in turn keeps frost from forming. It is with this “trick” that Bowdoin has been able to have fresh lettuce greens well after the season’s first frost. Even in the first week of December we still have radishes, salad turnips, spinach, and mustard greens in the ground.

There is a limit, however, to what one can get away with when it comes to winter production. As many of you know, the capacity to grow is greatly determined by length of day, not simply on whether or not plants will freeze. It turns out that most plants require more than ten hours of daylight in order to put on new growth. Anything less than this creates a condition of stasis, where established plants seem to simply rest and wait for better days. For this reason, Coleman advises to avoid sowing seed after October. In fact, for crops such as kale and spinach, it’s best to have established plants (individuals nearly harvest-ready) around this time in order to anticipate this slowing down. Once plants enter this holding pattern you will have something to harvest.

Growing vegetables for an educational institution is a great opportunity, and is itself an education for those involved. I am highly motivated by the promise of season extension, and look forward to refining it in practice here at Bowdoin. Meanwhile, be sure to head to the local farmer’s market and treat yourself to a fresh salad, a surefire way to cure the winter blues.

crops under cover

Row cover is extensively used in organic production