killing frost

annie77September 24, 2009


I am pretty new to gardening and I wanted to plant some wildflower seeds this fall but I keep seeing in various places that you must wait until the killing frost had passed. Can anyone tell me what the typical timeframe for this is and how to tell when it's happened? I live about 10 miles northwest of Boston.

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bill_ri_z6b(Zone 6B)

Annie, it's hard to predict when a killing frost will occur. I would suggest that you prepare a bed for sowing (tilling and raking etc.) and then when you've had a killing frost and the ground is chilly, but before it freezes, you could then sow the seeds. I would cover them only lightly with soil and then maybe a light covering of hay to keep them from blowing or washing away. Come the warmer days of spring you should see some sprouting and hopefully enjoy the flowers next summer.

    Bookmark   September 24, 2009 at 12:03PM
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You can take a look at these links for a good rough idea:
Regular frost dates?
Hard frost dates?
A discussion of the Boston frost dates and information at the links.

    Bookmark   September 24, 2009 at 8:31PM
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asarum(z6 Boston)

Anna: In addition to wanting to know when to expect a killing frost you were also looking for a way to know if you have had one. The definition of a killing frost is not precise because different plants can withstand temperatures below 32 degrees for varying amounts of time. A touch of frost happens when parts of a plants leaves get blackened by frost, but the plant doesn't die. If the weather warms up for awhile these plants may carry on for a long time although they don't look good. Then you will get a frost in which the most frost sensitive plants dies. If my memory serves me, I think morning glories are among the first to go. Some other annual plants will still be fine, but then comes a cold night or series of cold nights that kill off all or most of the annuals. This is what most people consider a killing frost. I think this is the definition that you can use for determining when to plant. However, for people like me who are gardeners with a large collections of plants, who are torn between cleaning up for the winter and not prematurely cutting off plants that are still doing fine, then killing frost is a long series of events. I go out and clean up plants over a series of many weeks as my non-evergreen plants slowly surrender to frost.

    Bookmark   September 25, 2009 at 1:05PM
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What asarum says is true, it does vary per plant. Suppose you are new and have no plants to go by??? I have read 28 degrees for four hours is a killing frost.

I suppose all the faint hearted as well as borderline tough guys will give up the fight with those conditions.

    Bookmark   September 25, 2009 at 10:39PM
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bill_ri_z6b(Zone 6B)

I think this thread has wandered a bit. Annie the idea of waiting to sow the wildflower seeds is to have the soil cold enough so as not to have them germinate now, but rather to wait until spring. While waiting for a "killing frost" is a reasonable suggestion, the idea is to sow the seeds when the soil and temperatures are cool to cold. As I said originally, go ahead and get the seedbed prepared. I would say you can probably wait until early to mid-november to sow the seeds. If we have a cold spell check that the soil hasn't started to freeze so that you can rake them in lightly. A light cover of hay or straw will protect them from washing or blowing away. Then, come spring, the seeds will know what to do.

    Bookmark   September 26, 2009 at 4:09PM
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