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Putting Perennials To Bed In The Fall

By: Teri Keith

Depending on where you live in the country, September, October, and November are the main months for putting garden beds to rest.  You may still have some warm days in these months, but once the nights and then days become chilly, it’s time to get to work. And, if you do it right, it is quite a bit of work, but more work now means less work later. Spring will be a breeze!

1. Weed

Pull as many weeds as you can in the fall to make spring gardening easier.

I have just started on the first step, which is getting all the weeds out, and it is going to take me quite a while.  Some seasons, I stay on top of weeding, and other times other priorities get in the way. This past summer was busy, so the weeds had a “field day.” It is especially important to clear weeds from right around the base of each garden plant. When weeding, it is wise to choose good tools for the job. Luckily, we have an excellent article written by my daughter, Jessie, that details the best weeding techniques, times, and tools for the job. Read it and weed! (Click here to learn how to week like a pro.)

2. Mulch

A moderate layer of mulch will protect against winter weeds, and protect perennials from the cold.

This brings us to step two, putting down fresh triple-shredded bark mulch, my preferred garden mulch, which I purchase in bulk by the yard or occasionally by the bag when only a small amount is needed. (Click here to learn about different mulch options.) Not only will mulch stop weeds, but it will also keep the soil moist, and protect your plants from big temperature swings. In addition, mulch breaks down over time, adding organic matter to the soil. Areas I have mulched for years have slowly turned into rich garden soil.  Put down around 3 inches of mulch, being careful not to cover the plant. (Not sure how much mulch to get? Click here for guidelines to calculate how much your garden will need.)

There are four rules to mulch application, particularly when it comes to mulching around plants: 1) leaf space around plants, 2) don’t mulch too thickly, 3) don’t apply mulch against the trunks of trees or shrubs, and 4) apply mulch when the soil is moist to make post-application irrigation easier. Leave a  3- to 4-inch gap between the base of the plant and the mulch, to avoid smothering the plant and causing crown rot. This is especially true of evergreen perennials and perennials with surface rhizomes, like bearded iris (Iris germanica hybrids). Peonies are also sensitive to excess mulch. One year, I mulched my peonies thoroughly in the fall and was so pleased with myself for getting it done early, but the following spring two of my prize peonies did not show up.  I had mulched too thickly and killed them. Also, do not mulch low, spreading, evergreen to semi-evergreen perennials, including Heuchera, Dianthus, ground cover sedums, such as ‘Angelina’. Mulching them commonly causes crown rot and death.

3. Cut Back Perennials

When frost takes your perennials, such as these hostas, it is time to cut them back. Semi-evergreen lamium (foreground) should be left alone until spring.

Wait until the frost has killed the leaves of herbaceous perennials before cutting them back and removing the old stalks and leaves.  This is especially important with hostas, one of my favorite perennials (I have hundreds!).  Unlike other perennials, if the leaves are removed while green, the plant will put up next year’s growth prematurely, and the following spring will have just a few scrawny leaves, so cut back hostas to 2-3 inches after the frost has taken them.

Evergreen perennials, such as Lenten rose (Helleborus spp.), myrtle euphorbia (Euphorbia myrsinites), and candytuft (Iberis sempervirens), can be left alone until spring, and semi-evergreen perennials, like coral bells (Heuchera spp.), dead nettle (Lamium maculatum), and certain daylilies, can also be left to trim back until the spring.

Some plants that add winter beauty to the garden should also be left alone.  Ornamental grasses, with pretty seed heads, gently wave in the wind, coneflowers (Echinacea spp.), black-eyed Susans (Rudbeckia spp.), and perennial sunflowers (Helianthus spp.) set seeds that songbirds like to eat in winter, so I leave them alone until the spring. Fall bloomers, such as chrysanthemums and asters, can also be trimmed in the spring. The protective stems of chrysanthemums sometimes help the tender perennials overwinter, which is nice if you like to keep them from year to year.

Another tip is to meticulously cut back perennials that are highly susceptible to leaf fungal diseases, particularly bee balm (Monarda spp.) and tall garden phlox (Phlox paniculata). Cut them back low, thoroughly, and be sure to completely remove the old leaves from the surrounding area. They should not enter the compost pile. Certain diseases can persist in the soil, even composted soil.

4. Divide and Plant

Divide large perennial clumps and spread them around in the garden to add more summer flower color where needed.

Mid-fall is the best time to divide and move hardy perennials, such as hostas, daylilies, monarda, rudbeckia, and coneflowers. If you live in USDA Hardiness Zones 3-5, or colder, divide and replant perennials earlier in the season, and only move those that are reliably hardy in your zone.  If you live in warmer zones, then you have a little more flexibility time-wise.

When dividing perennials, I typically use a sharp spade to neatly cut away a section of the plant. It is essential that each chunk has a nice portion of the crown with lots of buds on the top and roots beneath. Then I move and plant them in locations that have the right site conditions and need the color. Some falls are dry where I live in Indiana, so I am sure to irrigate my new divisions well when the weather does not bring rain. Adding Black Gold Garden Soil to the bottom of each hole adds needed fertility and a boost of fertilizer, which all plants appreciate.

So, I must get going to finish my fall garden cleanup, while the going is good (and so should you)! Then, I can spend the winter focusing on next year’s garden, worry-free.

About Teri Keith


Garden columnist, Teri Keith, has gardened for over 50 years in her home state of Indiana. She served as a longtime IGC nursery manager specializing in annuals and perennials in Bloomington, Indiana and still gardens with passion. Each year she plants and maintains over 50 flower containers, many gardens, and a large collection of lilacs.

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