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Serving Northern St. Louis County, Minnesota

Solar greenhouse has me gardening in December

Marshall Helmberger
Posted 12/3/15

For most folks in our area, the gardening season is pretty much wrapped up by the end of September— and that had long been the case for me as well.

Not anymore. Since building a solar greenhouse …

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Solar greenhouse has me gardening in December

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For most folks in our area, the gardening season is pretty much wrapped up by the end of September— and that had long been the case for me as well.

Not anymore. Since building a solar greenhouse last year, the gardening season, for me, now extends nearly ten months of the year, and with only minimal supplemental heating.

A solar greenhouse is different from most greenhouses, because the glass is mostly limited to the south-sidewall. The rest is framed, insulated and sheathed, so it’s designed to hold the heat gathered from the sun. Most greenhouses are all glass or plastic and they lose lots of their heat overnight. A typical greenhouse might hold temperatures, at best, eight degrees above the outside conditions. A solar greenhouse, like the one I built, regularly holds the inside temperature as much as 25 degrees above the outside air overnight. That means I don’t have to worry about below freezing temperatures in the greenhouse, in most cases, until the overnight lows begin to hit the single digits.

This year, thanks to an admittedly mild November, I had tomatoes, peppers, and eggplant thriving in the greenhouse until the week before Thanksgiving— and without any supplemental heat, other than what the sun provided for free.

While single digit lows finally nipped the sensitive plants in the greenhouse just before Thanksgiving, the hardier stuff is still going strong in the first week of December. The lettuce, spinach and other salad greens are looking lush. I just picked the last of the beets this past weekend, and there’s a ton of kale that I expect we’ll be harvesting until Christmas.

While our outside garden beds have been wiped clean by deer in recent weeks, everything in the greenhouse is safe from the furry competition. A few aphids are still hanging on, but they’re a minimal issue this time of year.

With a growing season now extending well into December, I only have a couple months of downtime before I’m ready to start planting again. Last year, I started planting March 1 and was picking salad greens by mid-April and green beans (yes, green beans!) by mid-May.

It’s only been a year, so I’m still learning the ropes of running a greenhouse. I’ve learned some things do better than others.

If you’re interested in learning more about building a solar greenhouse, I’ll be teaching a class on the subject at Natural Harvest Food Co-op in Virginia, in February.Watch for an announcement in the paper in late January. It will almost be planting time by then!