Plants grown indoors, even under very good light conditions, tend to stretch and become a little tender, partly because they are not exposed to wind. It takes plants about a week outdoors to adjust to wind stress. But researchers have found that brushing your seedlings before they go out will speed up this hardening off process.
"I strongly recommend that gardeners brush their transplants," says Joyce Latimer, a plant physiologist at the Georgia Experiment Station in Griffin. "It's the safest kind of hardening you can do, and the nice thing is that you can see the plants respond in two days. A brushed plant is shorter, stronger and more resistant to wilting. The leaves will develop closer together, and be smaller and a darker green. We've measured the growth and brushed plants put on the same weight as unbrushed plants, but everything is more concentrated."
Latimer says you should start brushing as soon as the cotyledons are fully expanded, even before there are any true leaves. Use a sheet of typing paper, a cardboard tube or a wooden dowel -- something wet leaves won't stick to -- and quickly brush the tops of a flat of plants, roughly 40 strokes in a minute and a half. Be careful with plants like peppers that hold their growing point above the top leaves. Ideally, do this twice a day until the plants are ready to go outside. Thankfully, no need to floss afterward.