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  • From: "William McKay" <bmckay55 AT hotmail.com>
  • To: market-farming AT franklin.oit.unc.edu
  • Subject: Re: greenhouse question
  • Date: Tue, 30 Jan 2001 10:17:48


I have been playing around with an unheated greenhouse (inspired by Coleman whose book, WInter Harvest Manual, I can not recommend enough) for three winters now. I am not a 'farmer' although I do grow about 1/4 acre and sell to a few restaurants.

I live in New England and in my area the low temperature for the winter is normally somewhere around -5F. Snow ranges anywhere from 15-20 inches to 100+ inches. This year so far we have had about 40-45 inches of snow and I have never had to remove snow from the unheated house. I have had to shovel snow from the sides where it was getting pretty high and blocking sunlight.

I have a couple of observations.

First, pretty much nothing grows from mid December to late January. It is not so much the cold, as the combination of cold and not enough sunlight. So, harvests for that period have to be well planned and planted in September and October.


Second the crops you pick are pretty important. I have had good luck with lettuce, beets, chard (an Italian variety I use which is very cold hardy), radicchio, arugula, and believe it or not, Rosemary. I have some rosemary plants which are going through their third winter and have survived -10. Coleman has a pretty good list, but things are going to vary from location to location. Also, within a particular type vegetable, some varieties do better than others. With lettuce, for example, baby sizes do better than full size lettuce (no rot develops where the leaves join the stem); loose leaf types do better than head lettuce (same reason); exception seems to be Marveilles des Quatre Saisons which is a butterhead, yet does well.

Timing is very critical. Coleman, for example, uses an inner tunnel of remay cloth. In zones 6 and above it not only critical to use it (pretty much prevents any soil freezing, you need to get it on early enough to prevent an initial freeze (we had a very cold spell this past november & early December, I did not have mine on, & consequently lost a lot of lettuce and radicchio). The same holds true for planting in the unheated house.

Heat & ventilation. These things get pretty hot. By the middle of February, the sun is strong enough to get them up to 100+ degrees on a good clear day. You need plenty of ventilation. If you are not going to use mechanical ventilation (I do not), the size of the house is critical. In order to get decent ventilation w/o fans, the length of the house can not be much more than 2-2/2 times the width. This limits you pretty much to 40-50 feet for a 20 foot wide house. They are unusable in the summer; I have mine set up so the cover is relatively easy to remove so I take it off in the summer, leaving the end walls up. I grow a short season crop, then put in my winter stuff in late September/October.

A couple of thoughts for having these unheated houses help with the bottom line. Coleman uses his pretty much to grow mesclun type mixes. Problem is, everyone and his brother grows mesclun. He also grows stuff like valeriana which are incredibly cold hardy. Problem is, I don't know too many people who desire that. I supply baby lettuce to some restaurants & the profit margin is much greater than for salad mixes. If you have high end restaurants in your area, this might be an option to explore. They are perfect since you plant them, they make a little growth, then stop growing and hold at the size you want. Certain Italian vegetables, also in demand by restaurants, do well in cold weather (chicory [radiccio] and endive). I suspect one of these houses would be ideal for forcing types of chicory and I also suspect you would command a high price for it. I think certain herbs would do very well if you had a local market for them; as noted, Rosemary survives and thrives in my unheated house; I imagine sage would do fine as would oregano and thyme. I bet parsley would do well also. These are all good 'winter herbs' and I suspect restaurants would desire them.


Bill McKay in E. Massachusetts
Seeds from Italy-importers of quality Italian Vegetable seeds

Thanks for posting this question.

I too have been going through the same frustrating process. It's far more
complex when you have a limited budget:)

Hope this stimulates lots of good discussion so we can all sharpen our
thinking.

One system that I am particularly impressed with and would like to implement
is Eliot Coleman's (author) greenhouse system. He has actually built one that
slides on rails so when it's time to harden plants just moves green house
away a bit longer each day.

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