The city gardener

Tips as you clean up the garden

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The days are getting shorter, the nights are getting cooler, and it’s just about time for fall garden cleanup. But is it better to rake leaves or mulch them? Clean up garden beds now or in the spring? Wrap shrubs tightly or let them breathe? Read on for some research-based tips for commonly-asked questions.
Our South Minneapolis neighborhoods have lots of beautiful mature trees, so fall means dealing with leaves. But whether you should rake or mulch (i.e. shred leaves and keep them on your lawn) depends on several factors. First, it’s overall preferred to mulch when possible. Tree leaves have a good amount of nitrogen, which is a very important nutrient for grass. So leaving shredded tree leaves on your lawn to decompose over the winter is essentially a free fertilizer application! Keeping leaves in place can also provide helpful winter habitat for pollinators, including some butterflies.
The problem with leaving leaves where they are is that if the layer is too thick, they can shade the lawn, reduce air flow, and reduce soil temperatures, slowing growth in the spring. So, if your lawn is more than 50% covered with leaves, it’s better to rake and bag them. If it looks like less than 50%, try shredding them with your lawn mower. After that, if the lawn is more than 20% covered with shredded leaves, rake some up and remove them.
Another thing you can do with shredded leaves is spread them on your garden beds (or you can purchase straw or other mulch for this purpose). Mulching beds over the winter suppresses weeds in the spring and reduces erosion from fall and spring rains.
Also, go a bit past your boulevard and remove leaves from storm drains near your house. Storm drains often become clogged with leaves, which can cause localized flooding during fall and spring rains. And if leaves flow down a storm drain and end up in the river, they can overload the water with nutrients, promoting excess algae growth and disrupting the ecosystem.
When cleaning up garden beds, it’s good to leave some healthy plant stalks, seed heads, and ornamental grasses in place over the winter. Pollinators and other wildlife will appreciate this food and shelter, and it adds winter interest to your yard. But make sure to check carefully for plant diseases and remove any spotted, rotted, or wilted plant parts so the problem doesn’t spread. Diseased plant material can be included with your yard waste pickup, since the temperatures reached at a municipal compost facility will kill the majority of plant pathogens.
When you mow your lawn for the last time in the fall, set the mower height a bit lower than usual, at about two inches. This will help air circulate around the grass blades, discouraging the growth of snow mold. Snow mold is a fungal disease that looks like patches of matted greyish or pinkish grass. If you see this in the spring, lightly rake the area to fluff up the matted leaves. But don’t worry – although snow mold does damage grass blades, the grass will generally recover as temperatures rise.
To avoid winter damage, consider protecting trees and shrubs. Deciduous trees (which lose their leaves in the fall) are susceptible to sunscald, which happens when the sun heats up the tree bark during the day, stimulating growth, but cold temperatures rapidly return at night, damaging the active tissue. To prevent this, wrap the trunk of new or sensitive trees with white plastic tree guards.
Evergreen trees and shrubs can be damaged by dry winter winds. Consider propping pine boughs or branches against evergreens, or constructing a barrier of burlap or other similar material. However, do not wrap evergreens too tightly – they need airflow and light to survive. Also, consider protecting small trees and shrubs with hardware cloth so rabbits and mice can’t eat them. Make sure the hardware cloth is high enough that when snow piles up, animals won’t be able to climb over the top.
Finally, fall is a great time to sit back and think about how your gardening season went. Did you plant any annual flowers or vegetables that you particularly liked (or didn’t like)? Gardening involves a lot of trial and error, so take notes on anything you want to remember for next season.
For more information, check out the University of Minnesota Extension Yard and Garden website. Extension resources are written by experts and contain the latest and most reliable research-based information. Happy gardening!

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