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Last Hard Frost Date?

Posted by ejr2005 Eastern MA (My Page) on
Sun, Mar 25, 12 at 10:15

How do you find out the "normal" date for the last hard frost? I know this year isn't normal, but ...

Follow-Up Postings:

RE: Last Hard Frost Date? has an interactive map which shows the average last frost dates for the state. I'm linking it below

also,in - if you click on the tab for the monthly forecast, then at the bottom, click on the tab for averages. Once you are in that scree, you can click on "record lows" and then table display - that will give you the historic lows by day for the month for your town.

keep in mind that low open areas are more susceptible to frost, whereas higher areas, protected by trees or houses are less susceptible to frost.

Here is a link that might be useful: average last frost date interactive map

RE: Last Hard Frost Date?

Thanks pixie lou! Got it from I was seeing maps but we're at a lot of the borders - just off 128 - and I couldn't differentiate the colors. I could put in the zip code at that site and voila - we're May 1-10. I'm thinking this year especially that's probably a good date to stop worrying. I don't usually worry about spring freezes, but this year my plants are so confused by this weather - as am I.

RE: Last Hard Frost Date?

This is a lot more information than you asked for, but some people may find it useful.

There are actually as many frost/freeze maps as people want to define. The usual variables are what temperature is being looked at, and how likely it is for that temperature to happen. For me, a hard freeze occurs are 28F, not 32F, even though most hardy perennials seem to have little trouble with temperatures that warm.

The second variable is how likely is that temperature to occur. An average frost date means roughly that it is as likely to frost after that date as it is before. While it might be useful for farmers who could potentially charge higher prices for an earlier crop, it is less useful for home gardeners. So the number that is usually talked about is 10%.

Here is a link that might be useful: NOAA frost maps

RE: Last Hard Frost Date?

Thanks mad gallica - that's great info too. I could zoom on on those maps to read them. It's weird - we're in Metrowest and in the May1 or after date for 10% or less probability but south of Boston (and pretty close to us) is in the May 15 or later box. I would think it would be the opposite. Anyway, by early-mid May we should have more clarity from the weather forecasts.

I'm most concerned about some baby hydrangeas that I had in the garage all winter. They're already leafing out - don't know what they'll do before mid May. We're be away a lot before then, so I'll have to leave them in the garage for some long stretches.

I also have one hosta that I thought was dead - it lost all it's leaves early last summer. Now it's leaves are about to unfurl. I'm not too worried about that thought - a couple of years ago I had a hosta in the garage that I forgot about for at least one summer if not two. I was experimenting to see if I could get rid of it's foliar nematodes. When I found it it had very large very white leaves. It's now thriving with no nems that I've seen.

RE: Last Hard Frost Date?

There is a cold spot that the weather folk always talk about I think down by the Taunton/Norwood general area. I think its due the low-lying aspect of that area??? Up in northern middlesex county close to NH, we go by May 31st, but I usually bump that by 2 weeks and just be careful. I think this year, I will bump it to May 1st and just keep watch. Will see how April goes.

You would think that shrub foliage could handle a little frost, but you are wise to protect it. I have had Hydrangea foliage damage in the past from late frosts. Its not pretty.

If you have a warm south-facing spot up against your house, that might be a good place to put borderline plants for now.

I have a 5' shelf setup loaded with potted perennials overwintered from the garage and elsewhere. There is a small amount of foliage. I don't plan on any extra protection, although it would be easy enough to throw an old sheet over the whole deal overnight. Maybe I will. But if I were traveling, I would just leave them alone.

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