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 soil-borne diseases, I would stop planting afflicted families there and pick something else. Prompt removal of diseased leaves and other good sanitation goes a long way, as does regular soil amending.
Q: Over the past several years, my lawn has been invaded by Japanese stiltgrass. Traditional lawn weed sprays have no effect, and the area is far too large for me to pull out individual plants. How do I fight back?
A: Stiltgrass, like crabgrass, is an annual, so the key is to provide a lush lawn to squeeze it out and break the annual cycle of weed seeding. It’s probably too late this year, so if you want to get rid of stiltgrass now in advance of grass seeding, you will need to apply a nonselective herbicide. Next March or so, you should apply a pre-emergent, though the timing for stiltgrass is a little earlier than crabgrass. You will need to find out the soil temperature at which seeds germinate, and you might buy yourself a compost thermometer, so you can track that next spring.
Q: We’re renovating our small backyard space and are hoping to have some climbing vines along our fences. Ideally, they’d be evergreen for some year-round color, but we’re also trying to plant mostly native plants. Some could be planted in the ground, but others might need to be in planters. The area is mostly partial shade. Any recommendations for your favorite climbing vines that would grow in these conditions? Relatedly, do you think any variety of lilac could grow in partial shade?
A: I am a big fan of the small-flowering but vigorous clematis (though sweet autumn clematis, now getting ready to flower, is an invasive weed best avoided). Carolina jessamine will take a little shade, as will the crossvine, both natives.
Q: My family moved into a house with a large, empty, fenced-in backyard. I love flowers, herb and veggie gardens, and lush landscaping, but I don’t know where or how to start building an oasis. We discovered a patio made from pavers under our grass, but other than that, I’m just struck by the gardener’s version of writer’s block. Do you have any tips, tools or books you can recommend for getting started?
A: My cardinal rule is to tackle one area at a time so that you don’t get overwhelmed. It makes sense to establish a patio area close to the house and attend to its environs. Another key bit of advice would be to devise on paper a master plan for the whole lot, so there is linkage and coherence to the overall scheme. Look for the books of two garden designers: Gordon Hayward here in the United States and the late John Brookes from England.
Q: Mowing our lawn is exhausting. We’re not even mowing any grass, just fields of weeds and weird greens that sprout up and grow with alarming speed. I’d love to turn our yards into areas that don’t require mowing at all, maybe wildflower patches or gravel gardens spotlighting low-maintenance plants. We have no idea where or how to start. Any advice?
A: Lawn mowing, on a square-foot basis, is the least burdensome form of gardening. Compare that with weeding or cultivating a patch of soil and tending to ornamental plants. Maybe you need a better, more powerful lawn mower. They make lawn tractors for the ultimate low-impact grass-cutting experience.
If you have a large lot, you can let the fringes go unmown to create a hayfield effect (assuming you live in a community that permits that). But letting a weedy yard grow tall is not a wildflower meadow. Meadows require careful installation and maintenance, especially when young. They are usually established with seed and plant plugs. It’s laborious and expensive. You can get expert advice in the books of two masters of meadow planting: Roy Diblik and Larry Weaner.
Q: We have drainage issues in our lawn, and I think the original French drain has had tree roots grow into it. It seems nearly impossible to get an excavator to come in and dig a new trench. I’m considering doing it myself. I think I should just put in a new drain rather than replace the old one. Any suggestions on how to approach this project?
A: If it’s 20 feet long or less and you’re fit, you could dig it manually. Tools I would use: thick garden gloves, a sturdy shovel and garden fork, a sharp ax (for roots), a wheelbarrow and, most of all, a mattock. The trench must slope a little and should be laid with a perforated pipe surrounded in gravel and wrapped in filter fabric. You can backfill a layer of soil on top, then seed or sod it. Pace yourself; don’t try to do it all in one go.
Q: I started gardening this year, like everyone else it seems, and it really is addictive. I’ve had success with tomatoes, jalapeños, chives, oregano, parsley and lemongrass, but some critter in my neighborhood seems to really like the taste of poblano peppers and mint. Right now, I have just a patch of dirt right outside my back door next to the house, but I’m thinking of putting a patio there, which would mean I would have to expand into my good-size, flat backyard. How would I start that? Should I get someone out with a tiller? Are those fenced kits with raised beds that I see online worth it? How would I water everything? I’ve got deer, squirrels, skunks, possums, raccoons, rabbits and who knows what else out there, and I don’t want to plant a field if everything will get eaten up by wildlife.
A: These animals can be physically excluded (with effort): skunks, rabbits, deer, possums and groundhogs. It is harder to exclude raccoons and foxes and impossible to fence out squirrels, in my experience. Chipmunks can be a real problem in large numbers. If deer and rabbits are a problem, you should fence them out before building a garden, and repellents do work. But most of all, don’t get fixated on all these animals in the garden. Gardening is a mode of living and is very enriching. Don’t fret too much about pests.