My favorite season is autumn. The weather is cooler, the sun shines abundantly, and I love the autumn colors of red, yellow and orange… and blue, purple and pink. Yes, that’s right, blue, purple and pink, and you can add to that magenta, rose, red-purple, royal blue, lavender and sky blue. These are all the true colors of autumn here in the United States due to one of our most glorious and prolific wildflowers, the aster.
What to do, what to do. Will I hurt anything if I cut it back? Should I leave seeds for the birds? Some of fall clean-up depends on how much of a neat-freak you are, how much credence you place in the winter-interest of dead perennial foliage and seed heads, and when you have time. As always, it’s a balancing act.
Removing the Dead
First, perennials that die to the ground are busy removing whatever they can of value from leaves and stems that are going to die at first frost or over the course of the fall. These sugars and starches are moved to the surviving underground parts of the plant to power up the new growth in spring. If you wait until the leaves and stems have yellowed or browned, then the plant will have scrounged what it can, and it’s fine to remove the dead stuff.
This removal is best done with a good, sharp pruner. With ornamental grasses, a string weeder or hedge shears will do the trick. If you wait long enough with some plants (after a hard frost–hostas and daylilies come to mind), the dead growth will easily pull off without your having to cut it.
Look at the foliage you are removing. If it’s full of spots (purple, brown, black), it probably has one or more fungal leaf spot diseases, which are common this time of year. I would set these out for trash pickup. With many fungi, the dead plant parts are where the fungus overwinters for re-infection next year, so sending these to the landfill reduces the chances of re-infection in the spring.
The main reasons to clean up in the fall are to remove these overwintering disease organisms; to reduce tramping around in the (usually) wetter spring garden; to get rid of unwanted seed heads; and because there always seems to be too much to do in spring and suddenly, the new growth is mixed with the old and the work is harder.
Note that many perennials overwinter with the start of next year’s growth above ground. Anything tight to the ground and looking new and healthy should be left alone. Sedums have little heads at ground level that look like very tiny cabbages, for example.
If you cut your grasses back this fall, cut them to about a foot tall. Too short reduces overwintering survival.
Plants that form a sort of a woody base or are evergreen should not be cut back in fall at all: many of the herbs: sage; lavender; rosemary; thyme. Also Iberis (candytuft), Gaura, Helianthemum (rock rose), and lavender cotton (Santolina).
I have been told that not cutting back the stems of Echinacea helps with overwintering survival as it tends to direct water away from the crown in winter. Heed this especially if you have planted some of the new orange/red/yellow cultivars.
Seed Heads for the Birds
On native plants, seeds can be left for the birds or for aesthetics. If you have a problem with reseeding (Chasmanthium grass, River Oats, Panicum grass – although it may be too late for Panicum – asters; goldenrods) then take off the seed heads now.
Although most people leave them on for winter interest, I recommend removing seed heads on Miscanthus grasses because they may seed out and become Invasive. This is a big problem south of here, and certainly occurs here with early-blooming cultivars.
What about the Leaves?
My own garden is under tall oak, hickory, and tulip poplar trees. I allow the leaves to remain where they fall and to decompose over the winter, spring and summer, except for the pathways. I pile up leaves from paths, groundcovers and lawns in the back of the yard, and eventually they break down to compost– even without kitchen scraps, turning, fertilizing and all the other trappings of the dedicated composter.
For further information
One of the best ways to learn about gardening is to join a garden club and meet other gardeners. In our area for example, the Beltsville Garden Club is quite active, and clubs are always looking for new members. If you are among the newbies that are learning that vegetable gardening isn’t as easy as it seemed it would be, then checking out a garden club may be the way to go. You might also investigate participating in the Master Gardener program if you want to really develop your own gardening expertise.
by Larry Hurley