Going Green in the Garden
The best non-toxic controls for 10 common garden pests and weeds
By Jodi Helmer
All gardeners have to deal with unwelcome intruders, from slugs snacking on hostas to chickweed choking out the marigolds. Instead of reaching for chemical-laden pest and weed controls, consider nontoxic alternatives.
Conventional pest and weed controls “often bring collateral damage in terms of harming beneficial insects and pollinators,” explains Jessica Walliser, horticulturist and author of Attracting Beneficial Bugs to Your Garden (Timber).
The good news: There are plenty of effective, nontoxic solutions to combat these top 10 unwanted insects and weeds.
Keeping Insects at Bay
Cabbageworms: These little green caterpillars with faint yellow stripes torment gardeners by chewing holes in the leaves of cabbage and other veggies including cauliflower, broccoli and kale, weakening—and often killing—the plant.
You can handpick cabbageworms off the leaves but Walliser suggests a less tedious alternative: Using a floating row cover, a fabric-and-wire tunnel that forms a protective half-dome over crops and keeps cabbageworms from accessing tender leaves.
Aphids: Colonies of aphids will attack plants ranging from geraniums and roses to tomatoes and peppers, killing foliage and stunting flower buds. You can squash the miniature insects or spray affected plants with non-toxic insecticidal soap.
“The best intervention is to clip off affected plant parts and compost them, because plant tissues never recover from heavy aphid feeding,” explains Barbara Pleasant, an award-winning garden writer and author of Starter Vegetable Gardens (Storey).
Slugs: Slugs are the most common garden pests, eating holes in leaves of flower and vegetable plants. Since slugs are nocturnal, it’s difficult to catch them in action; gaping holes in the leaves are a telltale sign that slugs are present.
Slugs like to hide in mulch; eliminating their habitat can help get rid of the pests. A shallow tin of beer near affected plants is also an effective control. Attracted to the scent, slugs crawl into the liquid and drown. (Be sure to keep pets from drinking the beer!)
When all else fails, Pleasant suggests using a slug bait made with iron phosphate to kill the pests.
Sawfly larvae: Adult sawflies are often mistaken for wasps but these insects are incapable of stinging. Instead, their larvae, which look like caterpillars, munch on the leaves and needles of ornamental plants such as roses, hibiscus and pine trees.
There are several different species of sawflies and larvae found throughout North America. “Many only [attack] one species of plant,” Walliser says.
You can pluck sawfly larvae off affected plants and squash the pests. Walliser also suggests using non-toxic insecticides such as horticultural oil, insecticidal soap or neem to kill them.
White flies: These pests often appear in colonies on the undersides of leaves. New growth is most susceptible to damage. Beneficial insects like lacewings often eat white flies, controlling their populations, says Melinda Myers, host of the television program “Melinda's Garden Moments.”
You can also get rid of white flies on flower and vegetable leaves with yellow sticky traps. The flies are attracted to the traps and stick to the surface.
Myers suggests avoiding over-fertilizing with high-nitrogen products that “encourage the lush succulent growth that most insects prefer.”
Chickweed: Chickens love chickweed. Without chickens to nosh on the small green leaves and white flowers, the fast-growing ground cover can take over the lawn and garden.
Chickweed robs the soil of nitrogen and attracts insects and viruses like thrips and tomato spotted wilt virus, doubling its destruction to plants and vegetables.
Attack young weeds with a garden hoe to keep chickweed in check. Pleasant also suggests using mulch to deprive chickweed seeds of light and prevents germination.
Crabgrass: Crabgrass is an annual weed that grows in clumps, choking out grass and plants and taking over the lawn and garden.
Myers suggests applying an organic pre-emergent crabgrass killer to the lawn—formulations that include corn gluten as the active ingredient are a good bet to prevent germination—but correct timing is critical. It needs to be applied in the spring, before crabgrass shows.
“If you miss the proper time you will be fertilizing the weeds,” Meyers says.
Raising the blade on the lawnmower creates more shade, making it harder for crabgrass seeds to germinate.
Creeping Charlie: The invasive groundcover is a perennial weed with petite green leaves and purple flowers. Known as ground ivy, the plant thrives in deep shade and damp soil and, if left unchecked, can form a dense mat that spreads across the lawn and garden.
A technique known as stale bed planting can control Creeping Charlie: Prepare the bed with organic fertilizer and compost, and leave it until the first Creeping Charlie seeds germinate. Once the weeds appear, kill them with a hoe or a vinegar-based herbicide. Then, plant the garden.
“With many of the weed seeds near the surface already germinated, you get better season-long weed control,” Pleasant explains.
Thistles: There are several varieties of thistles, including annual, biennial and perennial. The leaves often have sharp barbs on them, making it almost impossible to pull older plants by hand. And, since most varieties are drought-tolerant and fast-spreading, thistles can get out of control quickly.
Mulch can keep thistle seeds from sprouting. Aggressive weeding is effective, too. Myers suggests pulling thistles from the garden upon first appearance (before it seeds).
Quackgrass: A perennial weed with long, tapered blades, quackgrass grows in clumps and chokes out grass. Because quackgrass has an extensive root system, hand removal/weeding is almost impossible.
In fact, pulling quackgrass by hand can cause the underground rhizome, which looks like a root, to break off and germinate new plants. For this reason, applying herbicide is the recommended approach.
“Organic grass and weed killers labeled for controlling [quackgrass] only burns off the top [of the plant] but doesn’t kill the roots,” Myers explains. “You’ll need repeated applications.”