AO Gardener Series: What is ‘Hardening Off’ Anyway?

The team here at AO is excited to share that we’ll be featuring some new contributors here on the GROW blog, all geared to get you inspired to grow. With the season right around the corner, we wanted to offer a resource for anyone out there who wants to go green, whether you’ve never handled a spade to being a well-versed professional, we want to share the experiences of voices from all levels of green-thumbery!

If like me you started plants inside, than whether you did so under lights, on a bright windowsill or in a greenhouse – your plants will need to ‘harden off’. This is a gradual transition stage between the seedlings cozy indoor life where their environment was constant - to a more fulfilling yet exposed living out-of-doors where there are exposed to stronger elements such as UV rays, wind, rains, pests and fluctuating temperatures.

This stage is called hardening off because what actually happens is a thickening of the cuticle on the leaves so the leaves lose less water. It toughens them up and helps reduce transplant shock first off.  

The question of when to do this is different for all plants. But the best time to harden off a tender seedling is one week before you plan to transplant it outside. Depending on weather can be a factor as to how long it takes also.  

Start by taking your trays of seedlings outside into a shady area for half a day, than bring them back in. Gradually you increase the length of time over the next week that they are outside. You also gradually start increasing the amount of direct sunshine they receive, starting with morning sun, as it is less strong. At night your seedlings will retreat indoors until the very end of the hardening off period where they finally camp out under the stars. Come transplant time, your seedling should now adjusted and able to handle a day of full sun, and the dip in temperatures that happens at night.


Keep a mindful eye on protecting your seedlings from any extra stresses during this time. You don’t want them to get to the point of wilting as they will dry out faster from the sun and wind exposure than they were doing indoors. Should you see the leaves turning a bit white this might be a bit of sunscald, so decrease the amount of direct sun they are getting. Most plants will recover well from sunscald but while there is no need to panic, be aware as it will add stress to your plant, and they just won’t look as healthy. 

At the end of your hardening off period, choose a cooler day to transplant and water in well. (If this cooler day is right before a stretch of sun, than even better.) Morning is the best time to transplant when as plants prefer not to be watered right before the temperature dips at night, which decreases the soil temperature even more.  

And that’s that.  When hardening off, trust me, it’s better to be safe than sorry. Stunting your plants can make you lose them, and sun scald looks like neglect after all your TLC thus far. The act of moving your babies outside should feel really great, but if you are feeling a bit of empty nest – don’t worry cause you could start some brussel sprouts or winter veggies inside now if you like. 





OH HI! I’M SONJA – AN OVER THE MOON INFATUATED FOOD GROWER IN BEAUTIFUL SQUAMISH BC WHICH LIES IN THE PACIFIC NORTHWEST. I LOVE TO GET DIRTY OUTSIDE WITH FUNKY TUNES AND JUST FALL INTO THE MOVING MEDITATION / AMAZING WORKOUT - ALSO KNOWN AS VEGETABLE GARDENING.




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