In our first year at this house I promised Dave we wouldn’t have a garden, but by the time Memorial Day rolled around we had unpacked the seed boxes and he said okay I’ll make a little garden by cutting out the grass, will 6’x6′ be big enough? I only had green bean and basil seeds so it was the perfect size.
The toddler and I planted the beans, me pointing to the ground where to place them in the trough I made and we covered them and watered them.
Summer got busy, the plants grew and we ate the beans and basil, but it took awhile to realize that healthy basil plants grow a LOT of basil.
Almost all summer I had been putting “figure out what to do with basil” on my mental check list.
By early September I had finally found a recipe for the basil and figured out how I wanted to try drying it… I made a plan to do it tomorrow.
I went out to harvest the basil and it was… black?
What?
I pulled up google and it said basil goes black when it’s exposed to cold weather.
Cold weather? Like a frost? It was 32*F last night?
I did more digging and basil doesn’t like sustained temperatures below 50*F.
Then I figured out there is a website that tells you the weather historically and it said that overnight Friday was 46F and by sunrise the temperature was 39F.
I left my sleuthing skills rest after that and wallowed at the loss… but that experience gave me something I didn’t expect – a framework I still use today.
Let me explain…
Micro Climate – Our backyard garden is cooler than our front yard garden – so they have different temperatures both during the day and at night. The pots on my front porch also have a different high and low temperature because the bricks on the house provides warmth through the night (late afternoon sun for my front porch). All of these areas have their own “micro climate”.
When you zoom out on a map we are 4 miles away from the airport that determined the 39*F. When I watch my big thermometer on the back porch I can see we are regularly cooler than the airport.
What does this mean for me?
It means I expect to be 5F cooler than the forecast. Sometimes it could be less, sometimes it’s been more, but in general I make my frost plans based on that 5F temperature difference.
Duration – a fancy word that in this case means length of time the basil was below 50F. Our basil was below 50F for at least 9pm to 7am (10 hours-ish).
If the lowest temperature was just below 50*F for maybe an hour before sunrise it might not have been a big black mess, so temperature and how LONG it was cold mattered.
How do I use this information? I check the hourly forecast to see if the lowest temperature will get there at midnight or just before sunrise and then plan accordingly.
Once you start to know which plants are most sensitive and keep an eye on the overnight lows, the end-of-season frosts don’t catch you by surprise (as often – even the best farmers and gardeners get surprised by the weather – whether they admit it or not.)
That black basil taught me more than any article ever did. And honestly? I’m still learning.
If you want help thinking through your own garden — what to plant, when to start, and how to make it actually fit your life — I made a free garden planner that walks you through the questions I ask myself every season.
🌻 Laura
P.S. If your late-season garden looks a little pathetic, those cooler nights might be the culprit. Cold temps don’t kill tomatoes and peppers outright — but they definitely slow them down.
My takeaway: You’re a good gardener. It’s the weather who’s moody.
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