Q: I heard you on your radio show discussing a product called Messenger to make tomato plants stronger. As novice growers, we have many questions about how to use it and how it works.

A: Messenger(tm) contains a special protein that causes a plant to believe it’s being attacked. As a result, the plant, be it tomato, petunia or turfgrass, thickens its leaves and puts insect- and disease-resisting chemicals in its cells. This is much the same effect as when humans receive a vaccine to guard against disease. Other chemicals, even aspirin, trigger this “systemic acquired response” when applied to plants. You can buy Messenger locally at Hastings Garden Center. Online, Gardens Alive (www.gardensalive.com) sells the same product, renamed Green Guard.