Originally Posted by want4rain
what does 'harden the seeds off' mean??
To gradually introduce plants to their future outdoor conditions. Typically, outside in sunlight during the day, in at night. Eventually you will be able to leave them out all night long. Once they take that well, they can be planted in their permanent spot.
Or, ideally, a cold frame. Anything from a cardboard box with a corrugated plastic or glass topper, to a fancy "greenhouse" setup with the cover. Cut off bottoms of 2 liter pop bottles and you have a nice mini greenhouse for individual plants.
Otherwise, take them outside when it's nice and bring them inside when it gets cold, yucky or too windy.