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I have built a small greenhouse (unheated; Canadian zone 5). I built it so that I could have a place to go in winter where there are green leafy things to look at.

What are some pleasant-looking, broadleaved evergreen plants that would be suitable for an unheated greenhouse?

User1974
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  • Are you looking for pot plants or in-ground plantings? If in-ground, are you able to open the greenhouse's sides during the summer so that it stays at roughly the same as the outside temperature? Is the greenhouse in full or part sun in the summer? In the winter? – Jurp Oct 11 '18 at 23:06
  • I assume you mean ornamental evergreens? Is the greenhouse in a sunny situation (when there is any sun, that is)? How small is it and is it glass or plastic/perspex/polycarbonate (just trying to hazard a guess as to what the likely temperature inside, particularly overnight, might fall to)? – Bamboo Oct 15 '18 at 00:22
  • @Bamboo Ornamental evergreens sounds about right. I'm not so interested in coniferous plants though (broad leaves prefered). The greenhouse is south facing in full sun. It is a A-frame shape and is made of [6 mil poly](https://www.homedepot.ca/en/home/p.240-in-x-1200-in-cgsb-approved-vapour-barrier.1000166576.html). The dimensions are 14ft wide x 16ft long by 9ft tall. [Here is a photo of it when it was unfinished.](https://i.stack.imgur.com/7Djcq.jpg) – User1974 Oct 15 '18 at 01:57
  • @Jurp Good question. Potted plants are ideal. The greenhouse is seasonal; I take it down in summer (small backyard--no room). – User1974 Oct 15 '18 at 01:59
  • I read that your temperatures may go down to -20deg F - if you're only using 6ml poly plastic sheet and not twin wall greenhouse plastic, it won't confer much insulation overnight, so any pots inside the greenhouse are at risk of freezing without heating overnight, see here https://www.doityourself.com/stry/buygreenhouse. Also not sure whether the roof is plastic or solid...? – Bamboo Oct 15 '18 at 10:32
  • @Bamboo Usually the temperatue around here doesn't drop below -15degF. And yeah, I would only expect the greenhouse to be 2-3 degrees F higher inside the greenhouse at night. It's made entirely of plastic sheeting, by the way. – User1974 Oct 15 '18 at 23:04
  • @Bamboo For some perspective, kale occasionally survives the winter here, but those winters are the exception, not the rule. However, I suspect that if I shielded the kale from wind, precipitation, and moderated the temperature swiings, that it would survive (hence the greenhouse). – User1974 Oct 15 '18 at 23:08
  • Your problem is growing pots - at those temperatures, they're likely to freeze solid, and that will kill the plants because the roots will be frozen. – Bamboo Oct 15 '18 at 23:09
  • @Bamboo Fair point, although there ***are*** broadleaf evergreens who's roots freeze, yet they don't drop their leaves or die. Baltic and english ivy are an example. Also, for what it's worth, the frost line is known to be 3-4 feet down in these parts. – User1974 Oct 16 '18 at 23:18
  • In the ground plants cope with the soil freezing because they have a larger root spread and are surrounded by lots of soil, but in pots is a different matter... if all the soil in the pot freezes for a week, then all the roots freeze too, which kills the plant – Bamboo Oct 17 '18 at 09:57

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Some ideas:

  1. Cranberries, lingonberries, winterberry, holly, barberry, and heather
  2. Kale
  3. Strawberries
  4. Late-fruiting raspberries (ok, not evergreen, but the fruit can be late, which is a nice treat)
User1974
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    Holly and heathers would probably be happier outside, especially in *summer.* (And a holly tree would soon get too tall for a normal greenhouse, unless you prune it hard). There are varieties that are hardy down to zone 3 - though your choice of zone 5 holly varieties is not very large. – alephzero Oct 11 '18 at 18:37