It's official -- fall has arrived! There's a wonderful, cool edge to the air these days that tells me it's time to prepare the garden (and myself) for a rest. My friend Cayce lives in San Jose, California, land of eternal gardening. It's a beautiful place, but I don't envy her. In my cold winter climate I look forward to the respite that comes with the change of seasons, and I'm excited at the prospect of getting ready for it. Call me crazy, but I like having a concrete goal to reach for.
I start by taking a walk around the garden, making notes (real notes, not mental notes) about what should be divided and transplanted. I like to divide many of my perennials in fall for several reasons. First, the plants will come up next spring looking whole, rather than like pie wedges. Second, in fall I can clearly see how big things have gotten and where I have holes to fill. Believe me when I tell you that by late April I will not remember this. Third, cooler temperatures make it easier for the plant to recuperate from the trauma of root surgery. And fourth, recent transplants need extra water as they settle in, which fall rains happily deliver. Try to get your transplanting done at least six weeks before a hard freeze so roots will be able to establish themselves for next season.
Clean Up Annuals
After the first frost, pull up any annuals that have turned to mush. And don't forget to thank them for their service as you toss them on the compost pile. They bloomed long and hard for you, but their time in your garden is done. I suppose if you have one or two you're sentimental about you could dig them up and bring them inside to grow as house plants, but not all annuals are suited to indoor growing. Tender perennials like coleus, rex begonias, and mandevilla vine that are often grown as annuals in cold winter climates are the best candidates for overwintering indoors.
Cut Back Perennials
The tops of some of your perennials will die back after a frost or two; others will last until a hard freeze. Either way, cut back most of your herbaceous plants before snow comes. A good general rule is to cut back perennials to two or three inches above the ground, leaving only little stubs. But there are exceptions. Some perennials, like Shasta daisies, Jacob's ladder, salvias, and Oriental poppies, put out a new clump of leaves at their base when they finish blooming. Leave this basal foliage clump untouched for the winter. Woody or semi-woody perennials, like Russian sage (Perovskia atriplicifolia), butterfly bush (Buddleia sp.), lavender (Lavendula angustifolia), and bluebeard (Caryopteris x clandonensis) can be pruned back a little to neaten them, but don't cut them back to the ground. Other perennials that shouldn't be cut back in fall include those with evergreen or semi-evergreen foliage that persists through the winter, such as heuchera, bergenia, sea thrift (Armeria), hellebore, pinks (Dianthus), and rock cress (Arabis).
You may also want to leave some perennials standing in the garden to add interest to the winter landscape. Ornamental grasses look lovely with a dusting of snow, waving in a winter wind. The wide, flat blooms of Sedum 'Autumn Joy' turn a rich, rusty brown as they age and look like a dried flower arrangement in the garden. Globe thistles (Echinops ritro) not only look strikingly sculptural as their bristles catch the snow, but their seeds feed the birds. If you decide to leave black-eyed Susans (Rudbeckia fulgida) standing, do so only in moderation. While their seedheads look pretty against the snow and birds relish their seeds, they self-sow with alarming success.
Protect Container Plantings
If you're growing perennials in containers, you might need to give their rootballs some extra protection over the winter. Remember, plants in the ground have a great volume of soil insulating their roots. In a container, there's much less soil protecting the root ball, and your plants' roots may get too cold. Try wrapping a few layers of bubble wrap around a pot or taping sheets of Styrofoam insulation board to the walls of a rectangular container. And then, because that doesn't look so pretty, wrap the whole container in burlap.
Once everything is cut back and wrapped up, it's time to add mulch. Unlike with mulch applied in spring, go ahead and cover the crowns of all your plants with 3 - 4 inches of the good stuff. By ″the good stuff″ I mean either commercial, naturally colored mulch (I can't stand the dyed stuff) or leaf mold from the pile you've been cultivating since this time last year. You did read my piece on leaf composting last month, didn't you?
Once your flower garden is fully winterized, it's a perfect time to plan a winter getaway. Your plants won't need you until spring.
Ellen Zachos is the owner of Acme Plant Stuff (www.acmeplant.com), a garden design, installation, and maintenance company in NYC specializing in rooftop gardens and indoor plants. She is the author of numerous magazine articles and six books and also blogs at www.downanddirtygardening.com. Ellen is a Harvard graduate and an instructor at the New York Botanical Garden; she lectures at garden shows and events across the country.