This is the lone forsythia bush in my yard. Of course, the bright yellow blooms are an awesome, welcome sight in spring for gardeners hungry to get their hands dirty. But I have it there for another reason: it’s a “phenological indicator”. That’s what the geeks say, instead of just calling it a biological clock. It’s long been understood that plants and animals react in predictable ways to warmth, and you can use that fact to help time various gardening activities. In this case, you can use forsythia to time your weed preventer applications for lawns. Crabgrass seeds germinate just about the time forsythia blooms drop from the plant. And you need the weed preventer on the ground before the seeds begin to grow. Many other garden pests can be timed this way too. Check with your local cooperative extension office or master gardener program. They often can tell you when pests typically are active. Just take a look around your garden at those times, and make note of what’s in bloom. Chances are, that will serve as a good guide to when you should apply a controls.
The real reason this is so helpful is that you rarely see pests until it’s too late to control them (or control them easily). Once a borer is inside your cucumber vine, it’s too late. Once weed seeds have germinated, weed preventers are ineffective. So timing is everything.
Late summer to early fall may not be the showiest time for dandelions, but it’s the best time to eliminate them from your lawn. I usually avoid using toxic lawn chemicals, so I was curious to try the new Ortho Elementals Lawn Weed Killer sample that I received at the recent Garden Writers Association Symposium in Indianapolis. This broadleaf weed killer is made with naturally occurring iron. The active ingredient is iron HEDTA–or hydroxyethylenediaminetriacetic acid, for those of you studying organic chemistry!
The product works by creating iron toxicity at the cellular level. Because the mechanism of iron uptake is different in broadleaf plants such as dandelion from that in monocots such as lawn grass, the weeds die while the grass is unaffected. This naturally occurring chemical is reported to be safe for humans and other animals. Sprayed areas are safe to reenter as soon as the product dries. And further background research shows that iron HEDTA is not persistent, so it is quite friendly to the environment. Additionally, rather than spraying the entire yard, you’re supposed to spray only the dandelions (or other broadleaf weeds you want to eliminate), so much less chemical is used than with conventional weed killers.
The initial results are impressive. I spot sprayed dandelions in my yard this last weekend. In just 72 hours, they looked like the dandelion in the “after” photo below. The true test will be how much regrowth happens. The label indicates that for best results, two applications three to four weeks apart may be necessary. So I expect that the dandelions will regrow from the roots and need another shot of weed killer to wipe them out entirely.