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Garden Help Desk: Best practices for keeping a safe winter garden

By USU Extension - | Oct 23, 2021

Frost-killed perennial foliage and stems can be left over the winter to shelter beneficial insects, etc. but should be cut back before new growth begins in the spring. (Courtesy Meredith Seaver)

I have been reading several articles about how best to clean up your garden for the winter. In years past I have pulled up the plants, roots and all. However, I read a few articles that say it is better to leave the roots so they can break down naturally in the soil and you don’t lose the helpful microbes that live on and around the roots. Some also say you should leave the plants and not clean them up until spring so there are places for beneficial insects to over winter.

It depends. What do you want your flower beds and gardens to look like over the winter? How busy are you? Were your plants healthy? How late is it in the season and how quickly is the weather changing? Each practice has its pros and cons.

You can cut off your annuals and leave the roots in the soil. That certainly can help to loosen up soil over time by adding organic matter, and decaying roots will release some nutrients back into the soil.

On the other hand, you could be leaving plant material in the ground that might be diseased, especially if you’ve been growing the same kind of plants in the same places for a few years. Or tougher roots might not completely break down before you want to plant in the spring. It’s not a huge inconvenience to work around those roots, though.

There may be some microbes that are on the roots, but there are also usually at least some in the soil as well. Adding a plant-based compost to the soil is another way to add beneficial microorganisms to the soil if you’re worried about that.

Frost-killed tops of perennial plants can be cut back to the ground for a cleaner look, deadheaded to leave stems and leaf litter for beneficial insects to use, or even left "as is" for beneficial insects and resident birds in the winter. (Courtesy Meredith Seaver)

Leaving entire plants in place is less work now. Seed heads from spent flowers will provide food for local birds that spend the winter here and any plants with hollow or pity stems provide places for solitary bees to nest. Other insects, mostly harmless or beneficial, will lay their eggs to overwinter on the dead stems of annuals and perennials, and the stems and autumn leaf litter provide places for other insects and invertebrates to shelter for the winter. Most insects, mites and small garden critters are either harmless or beneficial but leaving the plants in place means you might also be sheltering pests and diseases, so you should never leave the tops or roots of any plants that were diseased.

There are some down sides to leaving plants in your flower beds. You may have to delay early spring planting, as bees and other insects may not have emerged yet. It can also be unsightly, so gardeners who want to leave things in place for beneficial insects, mites and small vertebrates sometimes choose to tidy up their front yards at least a bit and leave things in place as a haven for beneficials in the back yard. And leaving entire plants in your flowerbeds also means you’ve put off your cleanup and soil prep until spring when you also have other things, like pruning, that need your attention.

For two garden situations it’s always best to remove frost-killed plants, vegetable gardens and large container gardens where you want to reuse the soil. In vegetable gardens we’re usually growing the same small assortment of plants every year, so rotating crops plus cutting off and removing dead plants reduces the chances of many common pest and disease problems in vegetable gardens.

In large container gardens where you want to reuse the container and soil, remove annual plants, roots and all if the plants were healthy. In small and medium sized container gardens the soil may be so crowded with roots that you won’t be able to reuse the soil. You’ll save yourself time and frustration if you dispose of the plants and soil, clean the container, and start over with fresh soil.

I’m ready to do fall fertilizer for my lawn. Should I put extra fertilizer around the trees in the lawn so that they get fall fertilizer, too?

If the plants in large container gardens have been healthy, the plants can be left until spring and then pulled "roots and all" to reuse the container and soil for a new planting. (Courtesy Meredith Seaver)

A late fall application of nitrogen helps a lawn get a good start in the spring, but fall is not the time to fertilize trees.

Newly planted shade trees should not be fertilized their first year. Younger shade trees that were planted just a few years ago may need a light application of slow-release nitrogen each spring for a few years. Well-established or mature shade trees actually need little, if any, additional fertilizer and when they do, slow-release nitrogen in the early spring is the best way to provide that. Applying fertilizer to trees in the fall can stimulate new growth and also interfere with dormancy and winter hardiness.

Save your money and don’t apply extra fertilizer around your trees this fall.

Soil in small container gardens is usually too root bound to be reused in the container. The stems and dead flowers can be left for beneficial insects to use over the winter but the soil and plants should be removed in the spring. Soil from healthy small container gardens can be broken up and added to flower beds and vegetable gardens so that it doesn't go to waste. (Courtesy Meredith Seaver)

If container gardens haven't been healthy, the plants and soil should be removed at the end of the season and the soil shouldn't be reused out in the landscape. (Courtesy Meredith Seaver)

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