Mechanical stimulation is an effective way to make plants grow tougher and preventing excessive stem elongation (stretching). Brushing is the simplest way of treating transplants in the greenhouse. Like everything with plug production, it needs to be done just right to be effective, but it can be a useful tool.
How to brush: Brush across the top of the canopy in long gentle strokes. The best tool depends somewhat on the width of the bench. An unpainted broomstick is good because the leaves don't stick to it. A piece of 3/4 conduit inside a piece of 2 plastic pipe should work for larger benches because the plastic pipe can roll to prevent plant damage. Run the tool about 1/2 to 1 inch below the top of the canopy to lean the plants over gently.
See longer video.
How much to brush: The amount needed varies with the season. In spring, 10 times back and forth, once a day, is about right. In mid-June it takes 20 strokes. More treatment than that can damage the leaves. If you see damage, it is too much!
With a long bench, it can take a while to go to one end and back. That seems not to matter. We had the same effect whether the stokes came continuously or up to 10 minutes apart. The plants remember, and add up, the stimulus over a rather long time.
When to start: Tomatoes: Begin treating when the plants are about 2-1/2 inches tall. We have found little benefit is starting earlier, and the chance of damaging the small plants is greater. Starting later is not only ineffective, but the leaves are so big that they tear. If the plants have been treated starting at 3 inches, the leaves are hardened to the treatment and handle it well even when the plants are larger.
Cucumbers: Begin as soon as the cotyledons open, and brush for the next 5 days. It keeps the hypocotyl about 25% shorter.
The first day or two, a lighter treatment is a good idea. You will notice that the plants wilt immediately the first time. They recover quickly and don't wilt when they are used to being brushed. In fact, brushing pioneer Dr. Joyce Latimer considers this treatment to condition plants for the field. She does not harden them outside before transplanting.
When to brush: Brush when the foliage is dry but the plants are not wilted. Mostly, this will be before watering in the morning. We have found similar effectiveness in the morning and afternoon.
Back to Thomas Björkman home
York State Agricultural Experiment Station, 635 West North Street,
Geneva, New York 14456
July 30, 2010