Hardening Off Seedlings

Photo of trays of seedings
Four trays of seedlings waiting for their time in the sun!
With a month to go until Boulder County’s average last frost date, it’s time to start thinking about hardening off cool-season crops! If you have season extenders like cold frames, row covers, or Wall-o-Waters, you can even harden off a few tomatoes and peppers too.

Why Harden Off?

Plants are wildly adaptable, which is part of the reason they grow all over the planet, inside and out. But that means that the structure of the plant itself (from the thickness of its stem to how open its pores are) is different based on whether it was started outside in the sometimes harsh and variable conditions of early spring or indoors where light, moisture, food, and wind are constant. You can replicate some outdoor conditions for your seedlings by directing a fan at the seedlings as they grow and by putting them somewhere where the temperature is a bit variable, but they’re still in for a shock when they move to your garden bed. Read more