Fall is a great time to work on perennial beds. The rains have started, so you can get your spade down into the soil that seemed brick-hard all summer. Also, the cool, moist weather lets plants adjust to disruption without stress, so it’s easy on you and the plants both. Here’s a list of what perennials would really like you to do for them in the fall so they’ll be comfy through the winter and happy next spring.
Plant them
Fall is a good time to plant perennials so that they’ll get established during the rainy season and be ready to grow and bloom next spring and summer. Fall is also a good time to find really big, nice plants in nurseries.
If you have any plants you bought earlier this year still unplanted, get them in the ground now. Don’t leave them exposed to harsh winter weather with their roots above ground in a pot.
Move them
Have you been bothered by a plant that got too tall at the front of a bed, or too short at the back? Or the flower color is too much like the colors around it (we often buy our favorite colors over and over without thinking) or it clashes? Want to move a spring bloomer from here to a group of summer bloomers over there? This is the time to do it.
Prepare the replanting hole in the new area first. Then put a small tarp, or a sturdy rag, or a low garden cart close to the plant you’re moving. Dig all the way around the root ball and lift out onto tarp. If the plant is tall and will be in your face while you dig, cut it down some, leaving a foot or so of stems to grab onto for lifting and moving. Replant the whole plant if it’s young – in other words, a newly-made mistake. If it’s been there several years, consider dividing it now.
Divide them
Many perennials start to overcrowd themselves and choke out in the center after growing in the same spot several years. Dividing helps to reinvigorate the plant. Cut back the tops of the plant until you can see the growing sections of its “crown”, the area where roots and tops come together at the soil surface. Be sure to leave enough tops to use as handles for lifting the plant. Dig the entire plant up and set it onto a tarp or cart as mentioned above. Drive a knife or spade blade between the sections of the plant. The newer growth on the edges of the clump will be the most vigorous and healthy, and will be what you’ll want to replant. The old center core should be thrown away/composted. Replant only as much as you want, keeping in mind the speed the plant grew and how much room you have to give it. Give away or throw away as much as you need to. Remember that you’re in control, it’s your garden and the plant is there by your invitation. Don’t let a pushy plant convince you to let it take over your garden.
Remove Dead Foliage
It seems there is much confusion on when it’s time to cut the tops off perennials. Most herbaceous (i.e. non-woody) perennials die off above ground in the winter and sprout back up from the roots the next spring. Some of these have colorful fall foliage like trees and shrubs do, and are fun to watch as their colors change. Others turn ratty, slimy brown-black with the first rain. The rule on when to cut is “When it isn’t pretty anymore.” If the foliage is still green in late November and you like that better than seeing bare earth, leave it alone. (Think Penstemons and Fuchsias) If the foliage is pretty orange and red, why cut it yet? (Think Peonies and Geraniums) If the dried flower stalks appeal to you, leave them as long as you want. (Think tall Sedums) If you look at it and think “Yuck!”, cut it off. If you had recurring foliage disease problems, like mildew on Phlox and Monarda, cut it off, and put it in the garbage, not the compost.
Some perennials keep their leaves through winter, like spring-blooming groundcovers, Heucheras, Hellebores, ferns. These are trickier. Spring groundcovers, like Candytuft and Basket of Gold should be sheared after blooming. Ferns and Heucheras should be cut back in late winter before new growth starts. Hellebores need to have the old leaves pulled off individually as the new leaves come up to take their place.
Finally, there are the plants that have branches above ground all winter, and could almost be treated like woody shrubs. Lavatera, Caryopteris, Phygelius, and many Fuchsias will regrow from above-ground branches after mild winters, or freeze to the ground and regrow from the roots after hard winters. My personal preference is to cut these plants down in late winter to force regrowth from the base every year. The new growth is more attractive and graceful in shape than the old branches.
Kill Slugs
Slugs are going to be looking hard for food as the supply of fresh foliage becomes scarcer. Be merciless. Get them in their time of need, before some of them go dormant. Put bait down all around the crowns of cut-off plants, especially their favorites, like Hostas. They will actually burrow underground to eat out the crowns below the soil if you let them get away with it. Slugs will want to hide in any mulch you use so put down slug bait just before mulching.
Mulching
Mulching is gardening jargon for insulation. It means piling some organic matter over the root areas and up around the crowns of plants to help protect them from severe freezing weather, and to prevent soil compaction and erosion from pounding rains. If you use a mulch with good nutrient value, like leaves and compost, you can really help your soil quality and plant health as well. I’m not a fan of bark as a mulch; softer, faster-decomposing mulches are better for the soil and the plants. Adding more organic stuff to the soil surface is good any time of year, not just in fall.
Don’t Procrastinate
You may have the urge to put off moving, planting and dividing until spring. Fight that urge. The weather won’t be any better in early spring than it is now, maybe even worse. The plants will be much, much nicer next spring if you do the work now rather than then. If you don’t get the work done in early spring, then it’s too late and you’ve missed your opportunity for another year. Fall is a great time for gardening, so take advantage of it.