For more than 40 years,
But his new book, "Protect Your Garden," is aimed at gardeners of all persuasions. For this edited Q&A, we talked with Rosenthal about his latest endeavor, which provides a well-balanced overview of the most common garden problems: pests, disease, malnutrition and environmental stress.
You began studying horticulture by taking classes at the New York Botanical Garden. Do you still employ practices that you learned then?
The methods and technology have changed so much. It was a different time. One profound thing I learned was to be sensitive to the plant and actually look at the plant. Whatever is happening to it is reflected in the growth and what it looks like.
How relevant is your background in marijuana cultivation to the advice you give backyard gardeners?
The problems you face are problems that all green plants face. You use the same solutions with marijuana as you would with any other plant. The main things that damage marijuana indoors would be mites, white flies, aphids — the common pests you have with [other] plants indoors or outdoors. Mites are especially difficult to get rid of.
Do you plant defensively, using the type of euphorbia called spurge to deter gophers, for example?
I just haven't had many problems with pests. I had one plant that got attacked so badly that the aphids would literally drip off. We used my Zero Tolerance spray, and it would kill the aphids, and five days later they would be back. It was a nice plant, but it wasn't worth it. My solution was to cut it down. If a plant is constantly having a problem in a particular place, it might be you are just planting the wrong plant in that area. You just learn from that. Don't try to fight nature.
What other gardening secrets do you have?
Weed block material is not very effective. It's thin and tears. What I've done instead is get commercial carpet that's being thrown out. You lay it upside down, so that the carpeting faces down and the backing is on top. You put that right over the soil, just as it is. If you want to make it nicer, put gravel over it. You'll never have to weed again. Covered, it will last for 10 or 20 years.
Does marijuana have any uses as a companion plant?
Farmers used it for hedgerows between the fields because it grows tall very quickly. It slows down the wind, prevents erosion and creates a warmer place for the garden. It can over-tower other plants, but it seems to be a good community plant. It does create a healthy area. One thing that marijuana does: It gets the gardener out in the garden all the time.