The next part of our hardening off series is about how we decide “when is the right time” to start hardening off our plants.
Truth be told, most of this decision depends on your intentions and also your general gardening capabilities. For example, if you’re aiming to just transplant into the ground around last frost, most people would want to start hardening off one to three weeks prior to last frost. Then again, you might also find yourself with an overflowing grow room, getting some of your plants outside sooner might bring some much needed sanity!
There’s a point in northern spring when the daytime weather clearly shifts. There’s a change from sub freezing and 30 degree temperatures to where “typical days” reach into the 40’s, typically when breakup begins. That’s what we’re looking for, when temperatures are more consistently in the 40’s than in the 30’s. We’ve found that generally starts to occur 4 to 6 weeks prior to last frost, most seasons anyway. We are always prepared for it to go later, though, gardening at 65 north always likes to throw surprises our way.
For us, we’re looking to transition our plants into a temperature controlled greenhouse where we can ensure there are no dangers of frost. That means, we’re looking for the earliest possible point where we can start to harden off our plants to begin that transition. Our general goal is to start taking advantage of the free sun energy as soon as is reasonably possible, while also minimizing the heating costs involved with our greenhouse.
It’s important to remember that the “shoulder season” isn’t safe for your plants to be outside, all the time. These conditions will often bring lows into the 20’s, which are plant killing temperatures! If you only have outdoors or an unheated greenhouse, it will still be essential for you to bring your plants inside overnight. It’s not until low temperatures are consistently in the very high 30’s to low 40’s that we’d consider leaving our plants outside overnight. This is the main advantage of the heated greenhouse, it offers the gardener a “safe place” to stash their garden starts in the very early season. This is super helpful as we’ll soon be having large plants coming in, like squash, cucumber and all of our late sown veggies and flowers.
Also, we heavily integrate plant temperature tolerance into our hardening off processes. The most capable, cold tolerant plants are first to be hardened off, followed by those that are less so. If you want to “ride the wave” into our last frost with your plants, understanding that plant temperature tolerance is absolutely essential. If you’re still struggling to understand things like cold hardy, frost tolerant and what all that means, please check out our plant temperature tolerance guide linked below!
Oh, and surprise! We’re finally uploading to our YouTube channel we started ages ago. It would be huge if you gave us a subscribe over there. The channel will be heavy on the cold climate growing information & education and will hopefully provide our readers with a bit more context. We plan to do some “fun stuff” from time to time, along with walkthroughs, VLOG’s and our livestreams. Maybe more as we find our stride. As always, we appreciate your support!
Demystifying Cold Hardy, Frost Tolerant, Frost Sensitive and Warm Loving Garden Plants