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In a 6b zone I have to grow some annual and perennial flowers by the end of May, meaning that they must be flowering by then. I have tried to make a rehearsal of some sorts, but we had freezing temperatures until the first days of May 2016, so last year I have transplanted them a little late (they were grown indoors from seed). The result was that they came in flower in mid-July.

Some of the species are Tropaeolum majus (or minus), Centaurea cyanus, Lavatera trimestris and Alcea rosea and I was wondering how to protect them in case I want to plant them earlier, let's say in March.

My plan is to make raised beds and any advice on how to protect them is most welcome. I also have to mention that the land is on a north-faced hill, but the slope is barely noticeable in the area I will make the raised beds.

  • 6b gets down to -17 deg C? – Graham Chiu Jan 10 '17 at 22:16
  • -23 deg C. Historical low was -30 deg C. – Alina Jan 10 '17 at 22:25
  • And what temperature are you trying to protect against? – Graham Chiu Jan 10 '17 at 22:34
  • I guess it won't be lower than -5 deg C in March, since the average low is -1. The annuals don't need to survive the cold season and from the perennials I will select species that withstand the winter, that's why I'm interested in their protection only in March. – Alina Jan 10 '17 at 22:45
  • Are you going directly from indoors to in ground in the final location? – mpdonadio Jan 11 '17 at 14:27
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I don't know about flowers, but for vegetables, I like to use humidity domes. I just cut off the bottom of a milk jug, throw the cap away and put it over my newly transplanted plants, if it still frosts. This seems to work for fairly cold temperatures, in my experience (at least down to 23° F. at the side of our house, if not colder, which is to say -5° C.) There are many kinds of humidity domes.

You might try row covers, floating row covers, certain protective garden fabrics/cloths, a hoophouse, a greenhouse and such, to protect plants from frost. However, they may each have different ratings for temperature.

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    In France, they used to use glass cloches in the market gardens. – Graham Chiu Jan 11 '17 at 6:28
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    Newspaper is an incredible insulator. I use newspaper dampened and then row cloth. Problem with plastic or glass covers is frying your plants. If you don't get back out to the garden and remove these mini green houses, you can easily cook your plants. If you are able to do that then mini greenhouses work as well as row cloth. Newspaper single sheets, dampened then cover all with row cloth. If you forget to cover and if it is still dark, start the sprinklers before the sun comes up. Freeze damage mostly happens when frozen plant cells thaw too quickly. Sprinklers slow the thawing. – stormy Jan 11 '17 at 7:37
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    I tried the sprinkler method once. This is my observation: If you're going to do it, begin before any plants have frozen (or they may still die). It will probably coat your plants in scary-looking ice (the melting of the ice I hear is supposed to produce heat or something to protect the plants; I don't know if it's true). If you don't want to risk extra anxiety over scary-looking ice all over your plants, maybe don't do it. It requires a lot of water. If you have city water, that may be a huge expense, since you have to sprinkle for hours. – Brōtsyorfuzthrāx Jan 11 '17 at 17:28
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    I started the sprinkler while it was dark, but after it had already frozen (it didn't work; hopefully it works if you begin before then, but I can't say). If you have clay-type soil, expect a lot of water build-up. For fall frosts, I prefer just to cover them with blankets overnight. It works very well. For spring frosts, you probably want something gentler than a normal blanket; something that will let light and air through. – Brōtsyorfuzthrāx Jan 11 '17 at 17:47
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    @stormy are you saying that plants will cook under glass in near freezing temperatures? – Graham Chiu Jan 11 '17 at 20:06

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