Garden Primer: Last Frost Date, First Frost Date and Length of Growing Season

Remember a week or so back when I taught you all about How to Read a Seed Packet?  There was a lot of information, wasn’t there?  Two of the things we talked about were “Days to Maturity” and “Propagation”.  Here’s a quick refresher.

Days to Maturity:  How long it takes the vegetable to be at the point where you can harvest it.

note: Days to maturity is very important!   If your growing season in between frosts is 90 days and you plant tomatoes that take 120 days to mature in the ground after the last frost of the spring, you will NEVER see a ripe tomato.

Propagation:  How to start the plant.  It will tell you if you can start it ahead of time in pots (some plants DO NOT like to be transplanted) and how long before it can be planted outside you can do that.  It will tell you when the plant can be planted outside.

Typical phrases are:

“As soon as the ground can be worked” –When it stops being frozen and sopping wet
“Early spring”–When it starts feeling consistently spring like but still has cold nights
“After last frost” or “X weeks after last frost”–After your last average frost date (just google “last frost date” and the name of your county).
“Directly in garden”–Don’t try to transplant this, it doesn’t like it.
“When ground has warmed to”–A specific temperature might be given.
“Harden off”–this is a process where you slowly get transplants used to being outside by bringing them out a few  hours at a time over the course of a few days-I’ll be writing a post specifically on this process.

note:  Sometimes there will also be directions for when to plant a second crop for harvest in the fall.

Great.  Fabulous. . . except. . .

How do you know if you have enough days in your growing season to let that plant reach maturity?  And right along with that-what’s all this about “Last Frost”?  Don’t worry, figuring out the growing season for your area is actually much easier than you might think.

The first thing you need to do is figure out for your area:

“Average Last Frost”-the last date in the spring that you typically still get a frost
“Average First Frost” -the first date in the fall that you typically get a frost.

Before you start worrying, the USDA here in the United States has done most of the hard work on that for you.  They’ve compiled data, done statistical analysis and all sorts of other technical stuff to come up with the information so you don’t have to.  And it’s all available either online or with the help of your friendly local Cooperative Extension Office.

Finding it is super easy.  Go to the search engine of your choice (I typically use Google) and type in the name of your town (or the closest larger town) and the term “First Frost” or “Last Frost”.  For example I’d put in “Binghamton NY First Frost” and “Binghamton NY Last Frost”.

Doing that I wind up at the Cornell University Gardening Resources site where they have a color coded map-and I can find that for my area the average last frost occurs between May 10th-20th the average first frost is between Sept 20th-30th.  Of course the weather doesn’t like to follow a schedule-so the frosts could happen before or after those dates. I like to look at the worst case scenario–so I would assume that have between May 20 and September 20 as frost free days which works out to 124 days.

Does that mean I can plant any plant that has 124 days or less listed for “Days to Maturity”?

Although it’s a good place to start, that’s not necessarily true.  You do need to remember to factor in some of the other information on that seed packet.  Some vegetables-especially warmth loving plants like peppers, squash, tomatoes and eggplants-might say “plant 2 weeks after the last frost date” or “plant after the soil has warmed to X degrees”.

So at my house if you plant Luffa Squash (yes, the things Luffa Sponges come from) which take 120 days to maturity and need to be planted out 2 weeks after your last frost it most likely will NOT mature before the last frost.  Of course that hasn’t stopped me from trying to grow Luffa for the last 3 years.  I’m stubborn like that-and hey, I’m not really out anything for trying!

What can you do if you have a short growing season?

Find special cultivars.  The seeds you are likely to see in your local garden center are going to be the run of the mill most popular types.  Don’t assume that they are the ONLY types.  Sign up for some seed catalogs and you will be amazed at the various varieties that exist with all sorts of different growing seasons.

tip:  If you have a very short season look for cultivars that have words like “Early” in the name.  Those cultivars are likely to have been bred to mature sooner than normal.  “Early Girl” tomatoes for example are 59 days to maturity, where your typical Big Boy tomato takes 75 days.

tip:  Look for a seed company based in the same kind of climate that you are trying to grow in.  I often order from Pinetree Garden in Maine or Territorial Seeds in OR–if things do well in their test gardens I can assume they have a good chance of doing well in Upstate NY.

Also know that there are ways to extend your growing season on either end.  Starting plants inside on a sunny windowsill or under lights is just a way to get things some of their growing time before you reach that last frost date.  Row covers, hoop houses, cold frames and green houses are all ways to start your plants earlier and keep them growing later.  We’ll cover all of that in a future “Garden Primer” post.





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