Holding Cold

Our average last frost date is April 20th, with the normal outside date May 15th.

This year, we look like we'll be receiving regular frosts and even a few light freezes through May 8th at the minimum, although the forecast that far out is unreliable at best.  This could change at a moment's notice.

Still, I have plants downstairs that are starting to grow into the rafters (literally, the top shelf's lights are hung from the rafters, and the plants are now past the lights.  The cleome and red salvia are particularly large, and so pot-bound in their little cells that they're starting to crawl out of them.

When this happens to you--and it probably will at some point--cease feeding and supply only water.  You can also start the hardening off process under the lights at home.

First, put a fan on the plants to make the leaves and stems move.  Shift the fan regularly to put it full strength on different flats.  This will thicken the cuticles and stems, and train them to withstand winds.  Although you can only get a ten to fifteen mile an hour equivalent wind on them, this will be sufficient to begin hardening them for outside life.

Second, run your hands over the top of the plants lightly once per day.  Similarly, this will strengthen stems and leaves to withstand wind and other mechanical forces.  It will also slow growth slightly as energy goes to thickening the skin and stem of the plant.

Third, let the plants wilt a bit before watering.  This also strengthens the skin of the plant.

There's no substitute for sunlight and the plants will still need hardening off to the full light of the sun and the ultraviolet they haven't seen before.  However, at the very least you can accomplish some of the hardening before you put the plants outside.