Does Climate Change Mean I Can Start My Seedlings Now?

14 hours ago

Becky Sideman, in the MacFarlane greenhouse at the University of New Hampshire.
Credit Emily Corwin / NHPR

Those early hints of spring can call to a gardener like a siren song. Yet the urge to get one’s seeds into dirt can be dangerous: most seedlings won’t survive a single frost. To help with that, gardeners use 30-year averages that predict when the last frost will probably occur. The thing is, in New England, climate change has temperatures rising relatively quickly.

That’s left me – a reporter and occasionally impatient gardener – with a question: Does climate change mean I can start my indoor seedlings any earlier than the traditional 30-year frost averages recommend?

It’s getting pretty warm out after all, and I want to get my sprouted plants outside as soon as the soil’s warm enough. So, I took my question into a greenhouse at the University of New Hampshire. Here, Becky Sideman was at a lab bench. I breathed in that damp, quintessential greenhouse smell, and she began.

“The last frost is getting earlier, the first frost is getting later, but at the same time, my advice to a gardener would be –“

What I haven’t told Sideman is, I’ve already put my seeds into soil and watered them. It was barely March, and seventy degrees outside at the time. My heart sank when she finished her sentence.

“Don’t jump the gun.”

Sideman knows as well as anyone that New England now has 10 fewer days below freezing than it did 20 years ago, and average temperatures have risen 2 degrees here in 30 years. Still, she explained, climate averages are just that: averages. Weather, on the other hand, is unpredictable. Furthermore, seedlings are very sensitive.

Sideman said you might be able to start your seedlings a couple days earlier than the 30-year frost averages suggest, but nothing more.  “Obviously a frost is a death knell for crops,” she said. Many crops are also easily damaged by what she calls “chilling injury.”  

When it comes to that dreaded climate change, there is still a silver lining for gardeners in New England. The dates for the first fall frost have gotten later, meaning the growing season has gotten longer.

By the time I confessed to Sideman, she’d already guessed it: “you already started seeds.” Luckily, she went easy on me. And, she offered this advice: don’t let your plants get root-bound and leggy, waiting for late May to arrive. Get them in the soil, and if the temperature drops, cover them in row cover, and blankets.

Along with some crossed fingers, I’ll be giving that technique a try.