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The Cheap and Easy Greenhouse: No Heating Required

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In my last post, I discussed Peter Henderson’s 1875 greenhouse/hothouse plans for the wealthy. But Henderson deserves credit: he didn’t just write for the rich, he wanted people of every income to have a chance to grow a plentitude of houseplants and exotics.

After he’s exhausted himself on the subject of the Ideal Greenhouse, his Gardening for Pleasure continues with ideas for attached greenhouses and greenhouse-pits that need no artificial heating to hold the plants you would keep in a cool greenhouse. It’s advice that modern half-hardy and tender plant growers might use, since rising fuel prices make heating a greenhouse an increasingly expensive proposition.

The attached-greenhouse method only works in areas with relatively mild winters; Henderson wrote from Jersey City Heights, where it freezes and snows, but not inordinately. (New Jersey, whose car licenses still read “Garden State”, was at that time a huge market-garden area that served the massive population of New York City.) A small greenhouse attached to a heated building, properly constructed, says Henderson, will keep plants going in places where the temperature doesn’t fall below 25 degrees F (-4 C). It needs to be tightly glazed, and shielded from the north and north-west (if you’re below the equator, change the directions accordingly).

The pit greenhouse (which seems to be a kind of glorified sunken cold frame) is even better, Henderson says. “This is formed by excavating the soil to the depth of from 18 inches (45.7 cm) to 36 inches (91.4 cm), according to the size of the plants it is intended to contain. A convenient width is 6 feet (1.83 meters)…and of such length as may be desired.” He cautions that the ground must be dry enough that water won’t seep into the pit, and advises walling the sides of the pit  4  (10.2 cm) to 8 inches (20.3 cam) high with brick or planks.

“The back wall should be raised about eighteen inches (45.7 cm), and the front six inches (15.2 cm) above the surface, in order to give the nursery slope to receive the sun’s rays and to shed the water.” If glass is laid on top, and light shutters or half-inch boards  laid on top of the glass every evening, “it may be used to keep all the hardier class of greenhouse plants, even in localities where the thermometer falls to zero (-18 C). ”

While plants in such cool greenhouses won’t thrive lustily, they will be ready to go at the first sign of warm weather. That way, you wouldn’t have to grow out tender or half-hardy plants from small slips every year, or buy them new.  If I bestirred myself to make such a pit-greenhouse, I could  have the large collection of scented and flowering geraniums I’ve fantasized about, or keep beautiful brugmansias over winter reliably, and flower them before frost. I wouldn’t have to beg friends to babysit my houseplants when I go away in winter, either. (I don’t have central heating, so if temperatures fall below freezing, my houseplants turn to mush.)

Older technology has a lot to teach us. While we may not have the stay-at-home lifestyles or cheap help of past eras, many of these antique ideas make better sense than energy-eating options we are offered today.

7 comments

1 Amy { 12.30.08 at 2:31 pm }

The pit greenhouse is an interesting idea. It gets far colder than -18C where I live though. I suspect I’d have to use some fresh manure in there to keep things a bit warmer.

2 wayne { 12.30.08 at 4:23 pm }

I enjoyed reading your post. I gave up tring to heat our unattatched greenhouse where I work. But now I do nothing and that seems wrong to… need to take the middle road.

3 Pomona Belvedere { 12.30.08 at 4:50 pm }

Fresh manure is certainly a traditional way to get greenhouse heat, and hopefully you have a free source handy, Amy. Greenhouse heating by oil, gas, or electricity certainly seems prohibitive these days, so I don’t blame you for giving up on that, Wayne. If you do try the pit greenhouse, I’d be interested to hear the results.

I think a lot of the pit greenhouse parts could be found at salvage yards and in the back yards and basements in the neighborhood (although then of course you’d have to wait to get the windows and shutters before you sized the pit).

4 Sylvia (England) { 12.31.08 at 3:15 am }

I have a small plastic greenhouse next to the house, this also has a low wall in front of it and is about 2 feet below ground level. I also have other plants in the shelter provided by the walls but open to the rain. Providing I keep tender plants, in the greenhouse fairly dry I have been able to get tender plants like geraniums (pelargoniums) through the winter. But it has been colder, so far this winter, so I may have to replace some of the plants!

Best wishes Sylvia

5 Pomona Belvedere { 01.05.09 at 12:46 pm }

I’d be interested to hear a report on how your attached greenhouse does for you in colder-than-usual conditions, Sylvia. It’s always amazing to me how even a tiny difference in shelter or exposure can make so much of a difference to the plants.

6 Kathleen { 01.26.09 at 10:16 pm }

I wish I had a greenhouse of any kind but one of these actually might be doable. For now, I force most of my tender, tropical, plants into dormancy in my basement. I haven’t lost anything the past three years. I would love a greenhouse for the luxury of puttering on a cold winter day.

7 Pomona Belvedere { 01.27.09 at 1:35 pm }

In the same book, there was actually a basement greenhouse the author had designed – it was a house whose foundation had been dug out, but it had never been built. He was very pleased with himself for figuring out how to do this, you can tell, and it was used for pretty much the same purpose as your basement. Great minds think alike.

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