As we reach our way into early May many of us are just starting to consider planting out our vegetable gardens for the season. ‘Tis the season of warm days and cool nights, and occasionally sometimes dangerously cool nights for our summer crops. As your garden plants make themselves at home in your garden it is important to consider hardening off your plants before planting them in the ground. Think of hardening off as acclimating your plants to their new home. We make a point of hardening off all our plants before planting in our fields or selling to our customers but the idea is a helpful one for every home gardener to understand to ensure their garden’s success.
Most food crops are started in the stable protected climate of a greenhouse where they are sheltered from natural fluctuations that happen outdoors with temperature, wind, and light. When hardening off plants that have been kept exclusively in a greenhouse I like to place them outside in the early morning once temperatures have risen into at least the mid 50s. Ideally that first day out in the outdoor world is a bit overcast or maybe you have a space with some dappled shade so your plants can slowly get used to the brighter conditions. Even greenhouse glass or plastic filters a large percentage of light. Direct sunlight can be strong for those plants not acclimated to it so a nice slow adjustment period is helpful. Additionally, I try to avoid getting water on the foliage of plants when the sun is on them as this can act like a magnifying glass with the sun and potentially damage your foliage.
Being outside in the wind for the first time will jostle your plants around more than they have been in their cozy greenhouse environment. This movement will ultimately strengthen the stems of your plants making them sturdier for the season ahead.
Before dusk when temperatures tend to drop, bring your plants inside or somewhere with a bit more shelter. This can be accomplished by bringing your plants into a garage, shed, or other structure, or under a carefully placed piece of burlap that can act like a blanket for the night. A week is the recommended time for hardening off but a couple days is usually enough to do the trick and avoid any kind of stress to the plants that might set them back.
And lastly, before deciding the time is ripe for planting out your vegetable garden, forecasted nighttime lows are worth keeping your eye on. Many of our summer crops like tomatoes, basil, and peppers really do not like nighttime temperatures that go below the mid 50s. Usually we are in the clear in our region by mid-May, but extreme weather fluctuations do happen on occasion. A plant that has been properly hardened off is better able to ride through a cool night unscathed. If your plants are already planted in your garden, not to worry! A carefully placed piece of burlap with the help of some supporting garden stakes can be enough to keep your plants snug and warm through the cold night.