When is my last spring frost?

– Posted in: FAQ, Weather
12 comments

If this apple blossom gets frosted before it gets pollinated, it will never form an apple.

If this apple blossom gets frosted before it gets pollinated, it will never form an apple.

Usually, when you want to know your last spring frost, the experts send you to a hardiness zone map, a chart, or even the NOAA records, conceding that this will only give you a ballpark figure. If you really want to know your local last frost date, consult a neighbor–at least until you’ve kept records for several years and can answer the question from your own data.

What About This Year?

But even that will only give you an average date. How can you know what will be the last frost for this year, this spring? Ha! Trick question: you can’t know until it’s over, and then it doesn’t really help you. What do I mean by that?

Last Year’s Last Frost Determines This Year’s Sowing Schedule

By virtue of previous record-keeping, we know our last spring frost will be sometime in May, possibly even June. So we are careful to record every low temperature at this time of year, but we won’t know when the last frost for this spring will be until all danger of frost is past, and we look back over our records and say, “Aha! Such-and-such a date was our last frost.” So we plan our seed starting, seed sowing, and seedling transplants based on that date from previous years.

Gardening–or Gambling?

Why am I bringing this up? Because we have had such a long string of mild weather and frost-free nights, that we are starting to wonder if we’ve already had our last frost. The apple blossoms and the lilacs are starting to open. The old beech leaves have dropped and the new ones are opening, which entangled reported in a comment meant there would be no more frosts.
lilac_precocious
If there are no more frosts, we started our tomatoes too late this year. If there are no more frosts, I can pull the leaf mulch off my reblooming hydrangeas. If there are no more frosts, we can stop bringing in the container-grown rosemary and cannas every night. If there are no more frosts, I can stop worrying about the hostas, lilies, and bleeding heart emerging further from the ground every day.

I planted this dahlia in the ground. Today. Should I join Gamblers Anonymous?

I planted this dahlia in the ground. Today. Should I join Gamblers Anonymous?


This morning I discovered that the dahlia tuber I had given up on as dead was, in fact, sprouting. I considered potting it up to join the rosemary and cannas on their nightly migration back indoors, but decided to gamble instead. I planted it right in the ground. Yes, I planted it directly into the soil, knowing full well that our typical, usual last frost date is at least three weeks away. Talk about daring!

I’ve just taken a peek at the forecast, and they’re now predicting a low of 34F for Sunday night and Monday night. Thirty-four could very easily become 32F, and on a clear night, which Monday is predicted to be, it could drop significantly lower in this cold pocket we call home. If it does frost before the apple blossoms are pollinated, there will be no apples. The hostas will surely be singed. I have seen bleeding heart killed right back to the ground. The dahlia can be covered, but the lily stalks are too tall. Hopefully I will remember to bring the pots in, and we will be thankful the tomatoes are still under the lights, and not too big yet.

Gardening is only a refined form of gambling, after all. Sometimes the odds are fearfully against us; sometimes we win; but once the passion seizes us we are the victims of its fascination for life. ~Neltje Blanchan

About the Author

Kathy Purdy is a colchicum evangelist, converting unsuspecting gardeners into colchicophiles. She would be delighted to speak to your group about colchicums or other gardening topics. Kathy’s been writing since 4th grade, gardening since high school, and blogging since 2002.

In its own way, frost may be one of the most beautiful things to happen in your garden all year . . . Don’t miss it. Like all true beauty, it is fleeting. It will grace your garden for but a short while this morning. . . . For this moment, embrace frost as the beautiful gift that it is.

~Philip Harnden in A Gardener’s Guide to Frost: Outwit the Weather and Extend the Spring and Fall Seasons

11 Comments… add one

GARY SHELESKY May 18, 2009, 6:39 pm

KATHY ; DO YOU KNOW WHAT IS THE POINT THAT APPLE TREES AREN’T HURT BY FROST ?? I GATHER BY YOUR ARTICLE IT’S AFTER POLLINATION. I HOPE IT IS THE HONEY BEES HAVE BEEN VERY BUSY THIS YEAR AND ABOUT HALF THE TREES HAVE POLLINATED.
THANKS GARY

Kathy Purdy May 18, 2009, 6:52 pm

Gary, it’s actually more complicated than I’ve made it seem. Take a look at this site about Assessing Frost and Freeze Damage to Apple Trees. Apparently even after the flower has been pollinated, the fruit can be damaged, which I did not know before. I don’t want to cut open flower buds to check, but I guess a commercial grower would do that to assess the damage.

GARY SHELESKY May 18, 2009, 7:41 pm

THANKS KATHY, I’LL JUST HAVE TO TALK TO THE APPLE GROWERS UPSTAIRS FOR HELP. (NO FROST ) THANKS AGAIN ;GARY

GartenGrl at Cool Garden Things May 14, 2009, 2:14 pm

Hey Kathy, This is a nice blog and an interesting topic. I’m here in Michigan and I have always gone by the “after mother’s day” rule of thumb.
It had not occured to me that it might change…I just planted 4 flats of Marigolds and 5 flats of begonias…I’m a little worried now…
http://www.gartengrl.blogspot.com

Craig @ Ellis Hollow May 10, 2009, 8:33 pm

File this under: Do as I say, not as I do. Success with many tender plants depends as much on soil temps as air temp. Even if we don’t have any more frosts (I moved a lot of stuff back in or on to the porch this evening), the soil temps are still too cold for them to thrive. If we don’t get any more frost this year, but the temps keep bouncing between 60s in the day and 40 (or lower) at night, heat-loving plants you put in the ground won’t die, but they won’t be happy, either. Keep them in the cold frame.

Craig @ Ellis Hollow’s last blog post..Flower bulb labyrinth at Cornell

Donalyn May 9, 2009, 10:22 pm

It’s hard to restrain yourself when it has been warm for so long. I’ve fallen prey to lots of annuals, but they are all still on the porch – where I can cover them easily. My husband completely lost his mind and planted beans – they are several inches tall! He is eyeing the guest room sheets I think – they would be enough to cover those bean babies. :)

Donalyn’s last blog post..Too nice to stay inside

Kathy Purdy May 10, 2009, 9:18 am

Well, Donalyn, the dahlia is the only madness I indulged in myself. But all the plants that were seduced into emerging ahead of schedule, I don’t know if I can protect them all. Triage may be the order of the day. And it’s official now: frost advisory in effect for tonight.

Carol, May Dreams Gardens May 9, 2009, 10:07 pm

I’m wondering if we’ve had the last frost here in Indiana. I’m thinking of planting my tomatoes out tomorrow or Monday. We’ll see. I hope it doesn’t frost for you on Monday!

Carol, May Dreams Gardens’s last blog post..Mother’s Day Blooms In My Garden

Kathy Purdy May 9, 2009, 10:23 pm

Thanks, Carol. But really, what was I thinking?

Annie in Austin May 9, 2009, 10:06 pm

Hi Kathy,

Michelle and Elizabeth from Garden Rant tried the Eleanor Perenyi method and planted early~planted Deep, which worked for them. http://www.gardenrant.com/my_weblog/2009/04/dishing-on-dahlias.html?cid=6a00d83451bd5e69e201156f2c65bd970c

We lost Eleanor Perenyi earlier this week – planting a dahlia seems like the perfect thing to do.

Annie at the Transplantable Rose

Annie in Austin’s last blog post..Thought Pops, Edition 6: Roofs, Roots, Retrospection and Lavender

Kathy Purdy May 9, 2009, 10:23 pm

Annie, thanks for the link. I had missed that particular post. I think I’ll pile a little more dirt on the dahlia tomorrow. No way is it six inches under. Do you think it will hurt the sprout to be buried?

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