Morton Arboretum
The 17-year cicadas are past their peak in the Chicago area and will conclude their life cycle by the end of June, according to The Morton Arboretum scientists. The next step, they say, is to take advantage of their carcases and exoskeletons to help trees and plants thrive.
Dead cicadas make great fertilizer
Instead of discarding cicada carcases and exoskeletons in the garbage or landscape waste, Arboretum Plant Health Care Leader Stephanie Adams suggests scattering them on lawns or garden beds as fertilizer.
“They serve as great fertilizer as they decompose,” she said. “This pulse of nutrients from the cicadas will cause a burst of tree and plant growth the next year.”
Cicadas can also be added to a compost pile, but not alone. Mix them with green plant material, such as weeds or lawn clippings, as well as dried leaves or other brown material, Adams said.
“Keep the pile moist and turn it often to aerate it so the insects break down more quickly,” she said. “An unturned pile of dead cicadas will stink more.”
Remove protective netting from trees once cicadas are gone
When the female cicadas cut slits on thin twigs to lay their eggs, this process can damage young, small or unhealthy trees and shrubs. Tulle fabric or other fine-mesh netting used to deter egg-laying should be removed when cicada activity ceases.
“Once the cicadas are gone, remove the netting promptly,” Adams said. “Even though it’s mesh, it’s still blocking some sunlight from reaching the trees.”
New tree branches that were bent by the insect netting will later reorient to their normal growth habit, she added.
Post-cicada tree care
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, Adams said.
Water trees and shrubs regularly 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, avoiding piling it against the trunk. The mulch will insulate against extremes in temperature, prevent soil moisture from evaporating and protect the tree’s roots and trunk.
Adams recommends monitoring trees for signs of dying branches, also known as “flagging,” or other problems caused by cicada damage, including small spots of brown leaves distributed around a tree’s canopy. Damage is likely to appear this year and into next year due to affected trees having fewer stored resources by then, she said.
“Because the egg-laying only affects small, easily replaced twigs, the damage is rarely serious except on some very small trees or shrubs,” Adams said. “For appearance, you may want to prune dieback from small trees or shrubs. On large trees, the dead twigs and leaves will break off and fall by themselves in time.”
For more expert tips about trees and cicadas, visit mortonarb.org/cicadas2024.