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Tidy up your garden after cicada invasion

As the great cicada emergence of 2024 nears its end, it’s time to tidy up and give thanks. “Overall, a cicada emergence is probably a good thing for gardens,” said Stephanie Adams, plant health care leader
at The Morton Arboretum near Lisle.

When the cicada nymphs tunneled out of their home down near tree roots in May, “they aerated the soil,” Adams said. That made it easier for air to reach plant roots and beneficial organisms in the soil. The discarded exoskeletons from the nymphs and the bodies of adult cicadas will add nitrogen and other important plant nutrients to the soil as they decay.

It’s true that the female cicadas have been making slits in small twigs of trees and shrubs to lay their eggs. But mature trees can shrug off such injuries and grow new twigs. Even small young trees and shrubs are unlikely to die, although their growth may be set back if they were heavily damaged.

The cicadas will almost certainly be gone by the end of June. As their song grows softer, here are some tips for dealing with the aftermath.

Sweep them where they will do some good. If exoskeletons or dead cicadas accumulate on steps or sidewalks, clean them up to avoid a slipping hazard. “A broom and dustpan or even a snow shovel will do the job,” Adams said. Instead of discarding the cicadas in the garbage or the landscape waste, scatter them on lawns or garden beds where they will decay to enrich the soil and feed plants’ roots. The chitin that makes up their shells consists of protein that breaks down into nitrogen. The odor of decay will only last a couple of weeks.

Turn compost often. “Cicadas are a fine addition to the compost pile,” she said, but not alone. You will need to mix them with green plant material, such as weeds or lawn clippings, and brown material, such as dried leaves. Keep the pile moist and turn it often to aerate it so the insects break down more quickly. “An unturned pile of dead cicadas will stink more,” she said.

Remove netting from trees promptly. Ghostly trees swathed in fine netting to deter egg-laying cicadas have been a common sight in leafy parts of the Chicago area for the last few weeks. Once the cicadas are gone, remove the netting promptly. “Even though it’s mesh, it’s still blocking some sunlight from reaching the trees,” Adams said.

Use the netting for crafts. Both insect netting and tulle fabric are made of synthetics and are not recyclable. However, they are washable (cold wash and cool dry). If you don’t want to save the netting to protect plants against future pests, you can use it for crafts. Adams suggests hats, dolls or ballet tutus.

Keep trees healthy. Plants are better able to handle any kind of stress — including slits in their twigs — if their general health is good because they have the resources they need. Water trees and shrubs especially if they were planted within the last two to three years. In dry spells, water large, mature trees too. Spread an even, wide layer of mulch 3 to 4 inches deep around a tree, without piling it against the trunk. The mulch will insulate the soil against extremes in temperature, prevent soil moisture from evaporating, and protect the tree’s roots and trunk.

Watch for rabbit damage. All kinds of predatory animals, including birds, squirrels, raccoons, skunks, foxes, and coyotes, have been enjoying a feast of cicadas. It may keep them too full to bother with their
usual prey, such as rabbits, leaving more rabbits to feed on garden plants. The best way to exclude rabbits from a part of your garden, such as the vegetable patch, is with a chicken-wire fence 2 feet high.

Monitor trees for dieback. Twigs that were slit for eggs may die back, showing as small spots of brown leaves in a tree’s canopy. Some of these small branches may break off. “The damage is less likely to
appear this year, because the trees have stored resources,” she said. “You’re more likely to see it next year.” Because the egg-laying only affects small, easily replaced twigs, the damage is rarely serious
except on some very small trees or shrubs.

For tree and plant advice, contact the Plant Clinic at The Morton Arboretum (630-719-2424, mortonarb.org/plant-clinic, or plantclinic@mortonarb.org). Beth Botts is a staff writer at the Arboretum.