Right now, some of our flower gardens are driving the Martha types a bit up the wall. They see flowered out perennials, plats with downy mildew, leaves going brown and the garden full of windblown leaves. They can hardly wait for a hard frost to cut the whole mess down. Then there is the laid back gardener who just walks away and leaves it for another day. There is a happy medium.
As long as there has not been a hard freeze, there are still plants with green leaves that are growing and making carbohydrates and sending them to the crown of the plant. Cutting these off reduces the energy reserves the plant has going into the winter. These reserves are needed for the plant to fuel new growth next spring.
Some perennials, if their tops are cut off while in the growing season, will attempt to regrow. Especially if we have a warm fall. In doing so, they deplete the energy they need to regrow in the spring and may not survive the winter. Or, at least, have a reduced growth/flower next summer.
Mums in particular don’t do well if cut down in the fall. Dr. Neil Anderson, a mum breeder from the University of Minnesota experimented. He cut some mums down after a hard freeze and left others alone. The plants left with all their top growth all winter were much more likely to survive.
These are plants that provide winter interest.
Many perennials have relatively strong stems that stay upright all winter. Some bees and other beneficial insects winter in those hollow plant stems. That means that in the spring you don’t burn those stems. Cut them off and leave them in an out of the way spot till July.
Plants in the daisy family, like coneflowers, provide winter feed for birds and other wildlife. Goldfinches especially like them. An aside — one of Bunkey’s neighbors complained that all he had in his coneflowers were LLBs (little brown birds difficult to identify), but no goldfinches. Bunkey explained that those were probably goldfinches “they all turn olive colored in the fall.”
“You mean the females. All the males go south you know,” declared Floyd.
It took some convincing and two bird books before he believed Bunkey that he had both sexes in his garden.
Heliopsis, some ornamental grasses, the fruit capsules of Siberian iris are also very pretty in the winter landscape. Some plants like bee balm, daylilies and peonies can have their foliage removed with no bad consequences. If there is no disease, leaving top growth on most herbaceous perennials is the easiest way to manage them throughout the winter. It is much easier to cut them off in the spring when they are quite brittle.
You will need to remove any diseased plants and leaves especially any that have downy mildew. Even for the marginal perennials, removal of sick leaves may help it next spring. Don’t put this material in the compost, bag or burn it.
The next step is mulching. Put a foot of leaves on the flower garden. The stems you left will help keep it in place and also hold snow keeping your plants from frost heave, sure death to the roots. Don’t pull the mulch off next spring. Plants will happily pop up through it. It keeps the roots cool, holds moisture and keeps weed seeds from sprouting. It also adds micronutrients as it rots. If you let annuals reseed, don’t mulch that area. Leaving plants standing in the garden is one less fall job. Yeah!
Bev Johnson is a Master Gardener with the University of Minnesota Extension. Her column appears in the Weekend Edition.