Fall is the time to start getting your perennial garden ready for winter and next spring. If you’ve planned your garden well, there still should be some plants flowering such as sedums and fall asters. A garden that has been well-maintained all summer shouldn’t require much work in the fall. However, if your garden has become overgrown and weedy, now is the time to clean it up. I like weeding this time of year, as the weeds won’t grow back.
Fall in the Perennial Garden
Continue to keep up with dead-heading (cutting off spent flowers), de-leafing (removing dead or diseased leaves), and weeding. If possible, it is best to wait until spring to cut back perennial leaves and stems. Many have a nice fall and winter effect (many ornamental grasses and bee balm), may provide seeds (asters, Joe Pye weed) or habitats (grasses) for wildlife, and will recycle nutrients back into the soil. Since spring is usually very busy, you may want to cut back in late fall just to save time, which is what I often end up doing. Especially cut back any perennials, such as some daylilies, whose foliage has become unattractive.
You may have noticed that some of your spring and summer flowering plants have grown a clump of green leaves at their base (called rosettes) after they were done blooming. Plants of this type include asters, tickseed, perennial sage, and beardtongue. Don’t cut those small rosettes back for the winter as plants will grow from these next spring.
There are certain perennials which are considered evergreen and also should not be cut back in the fall. These include bugleweed, rock cress, sea thrift, wormwood, heart-leaf saxifrage, pinks, barrenwort, spurge, hellebore, coralbells, dead nettle, creeping phlox, some primrose, lungwort, saxifrage, creeping sedum, hens and chicks, and thyme.
In early fall, spring flowering (and maybe some summer flowering) plants can be divided and transplanted. Don’t wait too long, though, because plants need to become established and well-rooted before the winter. If you didn’t get to it in late summer, you can divide your Oriental poppies, bearded iris, and peonies now.
Now that the heat of summer is over, it is a good time to plant if you didn’t get it all done in spring, or if you bought more! Don’t forget to plant some spring flowering bulbs now too. Most hardy ones are perennial, except for most tulips. If you want tulips that will last several years, look for ones marked as perennial such as the Darwin hybrids. Daffodils are a good choice if you have deer nearby, as they won’t bother these bulbs or flowers.
Take a walk around your gardens and write down ideas for next year and plants that will need dividing in the spring. It also might be good to notice what plants worked and which ones didn’t do so well, and note what the environment was like for that plant (dry or moist soil, sun or shade, etc.). If a plant really didn’t do well and you know you want to get rid of it, throw it out now to allow room for something new in the spring.
If you want to create new beds next year, now is a good time to cut the sod. If the area is small you can probably dig the sod yourself. For larger areas, a sod-cutter might be helpful. Check rental shops for these. Add compost to this new bed and work it in to start preparing the soil for spring planting. Add lime if called for by a soil test.
It is probably best not to fertilize herbaceous plants in the fall as they don’t need to get any extra boost in growing (unless they were stressed during the summer), but adding compost may be a good idea. Compost adds organic matter to the soil, helping to create a healthy environment for your plants, as well as adding some nutrition. Perennials going into winter in good health and vigorous will have a better chance of surviving than those that are weak.
Sometimes stores will have left over mulches or bulk compost and sell it cheaper than they would in the spring. You can buy some and spread it now, or pile it up and save it for spring.
If you like to give your plants extra winter protection, that should be done later in the fall before the snow begins. In areas that get ample snow cover, winter covering probably is not necessary. Snow acts as a natural insulator and will keep the plants near freezing. If you’ve chosen the right plants for your climate, they should make it through the winter with little or no injury. If you have tender plants that you want to give a little added protection, you can cover with straw (not hay which usually has weed seeds), pine needles, leaves (shredded, or else they may compact), evergreen boughs, or wood chips.
Still have some time? Then you could even edge your beds now to be ready for spring. Finally, clean and store your tools and roll up your hoses (make sure to get all the water out). Sharpen hoes with special files you can find at hardware stores, complete garden stores, or online. Make sure you’ve cleaned and properly stored power equipment as well. The more you do in the garden in fall, the more ahead and less stressed you’ll be in spring.
By Dr. Leonard Perry, Horticulture Professor Emeritus
University of Vermont