Washington Post Gardening columnist Adrian Higgins answered questions recently in an online chat. Here is an edited excerpt.
Q: What can the home gardener do about clover taking over a lawn? Last year, I fought crabgrass, and this year, it’s clover. Crabgrass was easier to pick out by hand. Any easier, earth-friendly remedies?
A: Clover isn’t so much a weed as a state of mind. If you come to regard it as a desirable component of the lawn, you won’t have to keep fighting it. Yes, there are herbicides that work against it, but it actually feeds nitrogen into the soil, is an important nectar source for pollinators and only gets expansive when the lawn is allowed to thin. Live with it, but push it back by overseeding the lawn.
Q: What is the best time to prune trees (suckers from plum trees and extraneous branches from a Japanese maple in a pot)? And must the cuts be treated with anything after pruning?
A: Most pruning of deciduous plants is best done during winter dormancy, not least because you can see the structure of the tree or shrub much better then. Other good times to prune are after the flush of spring growth and also right after flowering, so that you don’t affect bud set for the following season. One of the worst times for pruning is over the next few weeks, when cutting back could induce fresh new growth that will be susceptible to frost damage. Wound treatments are no longer recommended.
Q: I have about 40 Knock Out roses. Some have branches that look stressed: lighter green leaves and rust-colored spots. What can I do to address this? And on a related note, would this be a good time to fertilize the roses?
A: I have reached a point where I can’t look at another Knock Out rose. If you enjoy this overplanted magenta flowering shrub, more power to you. You might lay a modest top dressing of rose feed to keep its floral cycles going through the fall. This variety is prone to rose rosette disease, spread by mites. Remove infected plants to curtail its spread.
Q: This August, crabgrass has taken over my lawn. What steps can I take now to minimize the problem next year?
A: Crabgrass is a direct result of lawns that are too thin. Thick, lush lawns are your best bet against weed infiltration. Crabgrass is an annual, so you can either spot-treat or simply hoe them now, but you will have to renovate the lawn to address the problem. Count on using a pre-emergent herbicide in early spring with follow-up applications.
Q: I have a 25-by-25-foot community garden plot that I have divided into quarters, and I rotate my beds each year for a four-year rotation. But for a garden that small, is rotation actually beneficial?
A: Rotation is desirable but almost impossible in such a small garden. I would move varieties around as best you can, but if you see