Fall is a glorious time of year to work in the garden. It is the ideal time to take stock of your perennial gardens, correct mistakes and problem areas, dig up, rearrange and divide existing plants, add new perennials and shrubs, and plant spring blooming bulbs. Fall is also the ideal time to start new gardens, especially if you want to use Passive Bed Preparation
and take advantage of all of the autumn leaves. As fall winds down and this work is completed, you will turn to the task of putting your garden to bed. Don't rush it! So many people start thinking about doing this in September when they should be thinking about fall gardening. Putting the garden to bed is a gradual process that begins somewhere around the end of October and continues right up until the ground freezes which in our part of Connecticut is usually around the end of December.
WHEN DO YOU CUT PLANTS BACK?
The rule of thumb is: "If it's yellow or brown, cut it down, if it's green, leave it alone." The life force of a plant is in its leaves during the growing season. As the weather gets colder, this life force is translocated to the root systems of the plants. When this happens, the leaves change color. Then and only then do you cut them down. If you cut off perfectly good green leaves, you will weaken the plant and possibly affect its vigor and blooming the following year. Consequently, you can't just simply say "today is the day I'm going to put my garden to bed...." Wouldn't you know that it's not that simple! Because plants die back slowly, at different rates, cutting back your plants is a GRADUAL PROCESS. Once you have a hard killing frost (somewhere between the middle and end of October), the tender annuals are history. The cold hardy annuals such as Calendulas and snapdragons are still gorgeous. The hostas, perennial hibiscus, balloon flowers (Platycodon), and many other herbaceous perennials have already changed color and can be cut down. So, every few days, I go through the borders, garden sickle and pruning shears in holsters on my belt, and cut back whatever has turned brown or yellow. The rest, I admire, enjoy, and leave alone. Perennials can take an amazing amount of frost! There are even quite a few late blooming asters, Aconitums, Helianthus, and Korean mums that begin blooming in late October- this is their season to shine! Some plants are also reblooming beautifully. Catmint (Nepeta) and roses are usually in bloom and very happy in November. So are the repeat blooming bearded and dwarf bearded irises. So don't rush the process. Enjoy your fall garden to the very end. Cut back only what is brown or yellow. Don't obsess about it! The plants will clearly tell you what to do!
EXACTLY WHAT DO I CUT BACK AND HOW DO I DO IT?
Plants in the perennial garden can be broken down into a few categories, all being treated differently in late fall...
1. Herbaceous Perennials
These are plants that truly die down to ground level at some point in late fall. Decades ago, the dominant paradigm was to cut every herbaceous perennial back to ground level and haul the debris to the compost pile. Now, we suggest that you leave some plant stems standing, especially those that have a pithy or hollow interior, as they are home to our native tunnel nesting bees. 15” is the recommended height to support these important native pollinators. You can also practice “chop and drop”, where you chop up your plant debris and drop them back on the ground as mulch. This returns a lot of nutrients to the soil and adds organic matter. This link explains the how and why of this important process:
Plants with wiry stems or those that turn to mush after a hard frost, your best bet is to cut them right to ground level. Use a garden sickle- you will find it is much faster, more efficient, and easier on your hands. You cut them back all the way to the ground, and nothing is left but stubs. Before you cut anything down, ask yourself “Will I know where and what this plant is next spring?” NOW is the time to label your plants with permanent metal markers using a waterproof, oil-based marker.
2. Herbaceous Perennials that maintain Basal Foliage
Many perennials lose all of their top growth, but when you go to cut the brown or yellow stalks down, you will find green, lush, healthy growth at the base of the plant. Following the rule above, you would obviously leave these alone! What that means is that you will still have the ground hugging leaves of the perennials left in the garden. They will be easy to spot in late fall and even the following spring. (I still think it's a great idea to label them properly with metal labels). Examples of these types of perennials are Oenothera, Salvia, Penstemon, and Scabiosa.
3. Plants that Remain UP into the Winter
Many of perennials just don't turn brown or yellow despite hard killing frosts. These plants remain up during the winter.
a. Some simply are very cold tolerant and their tops don't succumb to cold until they have been exposed to a few months of winter. Nepeta (Catmint) is a good example of this. You never get a chance to cut it back before the snow flies because it still looks good. Come the spring, it is a matted tangle and gets cut to the ground to make way for a new crown to grow. It will be clear to you if a plant is in this category. It will still look good when you are "done" with your garden. No problem. Deal with it next spring!
German or Bearded Iris fall into this category but they require special treatment. Even though their leaves are growing actively and look green and lush until Christmas, you must not leave them up all winter long as the foliage harbors the larvae of the Iris borer. So go right to your December calendar and write on it "cut down German Iris" somewhere around the middle of the month. Bag the leaves and discard them. This is the easiest and most efficient way to control their enemy, the iris borer. Trust me, they will be fine and will still bloom next year.
Note: All other irises are cut back when they naturally turn yellow. Do not leave Siberian or Japanese iris leaves standing all winter as mice or voles love to nest in their crowns and eat the rhizomes. Shave them down to ground level with your sickle.
b. Some plants maintain a woody trunk and should not be cut back hard in the late fall. Instead, they should remain up all winter long. For these plants I simply cut back the tops approximately 1/4-1/3 to keep the plants from rocking in the wind and to shape them. Many perennial herbs such as lavender, rue, germander, sage, as well as the flowering perennials Russian sage (Perovskia) and Montauk daisy (Nipponanthemum nipponicum) fall into this category.
c. Candytuft (Iberis) and Hellebores are early spring bloomers that are evergreen all winter long. I DO NOT CUT THEM BACK IN THE FALL. Candytuft goes into the winter with flower buds set on the plant. Cut it back after blooming, in mid spring. Hellebores have semi-evergreen foliage. They look good going into the winter. By late winter, the leaves look tattered and cutting them down is one of the first garden chores of the year, as soon as the snow melts. If you suspect that a plant is evergreen in your garden and its leaves look terrific in December, leave it alone. It can add winter interest to otherwise barren borders!
d. Most ornamental grasses are left up all winter long because they look stunning covered with snow and ice and add winter interest to the garden. Cut them back to within 12" of the ground in late March. Exceptions are ornamental grasses that may self-sow and become problematic.
e. Kniphofias (Red Hot Pokers) require a special treatment. DO NOT cut back their leaves in the fall. Instead, in late November, gather up and tie the leaves together with twist ties or twine. This keeps water out of the crown. In the spring, cut the foliage back to the base.
The decision to remove or leave seed pods standing for the winter is based on many factors. If the seed pods of a plant feed winter birds (Echinacea, Helianthus, Rudbeckia), you may decide to leave them standing. If a plant has self-sown in your garden and you don’t want any more in that location, you should remove the seed pods as they ripen. You can drop the seeds in a new location if you want to add more to a different garden bed. Some seed pods are ornamental (Belamcanda, Rudbeckia maxima) and are often left up for winter interest.
Flowering shrubs fall into two basic categories:
1. Shrubs that bloom on previous year's wood. These are spring bloomers whose buds are set the year before. NEVER prune these in the fall as you will prune off next year's flower buds. Examples are azaleas, lilacs, rhododendrons, and Fothergilla.
2. Shrubs that bloom on current year's wood. These are summer and fall bloomers. Even though it may not hurt them to be cut back in the fall, I usually wait to do so until spring so as to leave some more winter structure in the garden. Examples include butterfly bushes, St. Johnswort (Hypericum), Abelia, and rose of Sharon.
Hydrangeas are a complex category. The blue and pink snowball types (Hydrangea macrophylla) should be left alone and possibly even wrapped if they are in an exposed spot. The older varieties bloom off of last year's wood. Newer repeat blooming varieties bloom on old wood and new wood. Wait to prune them until mid-spring. Even though they look pretty dead by November, leave them alone! Smooth hydrangeas (H. arborescens) and panicle hydrangeas (the tree hydrangeas) bloom off of current year's wood. They are left up all winter and pruned in the spring. Oakleaf hydrangeas (H. quercifolia) set up their buds on the tips of this year’s wood. Do not prune them in the fall.
I treat roses like flowering shrubs and leave them alone, cutting off only the wildest shoots, saving the heavy pruning and shaping until spring. In late fall, just before the ground freezes, HILL UP SOIL OR COMPOST AROUND THE BASE OF THE ROSES to about 12-18". This protective measure assures that even if the tops of the roses die down in an extremely cold winter, the plant beneath the hill will still be alive in the spring. This is not necessary for any roses that you have had in your garden and have proven winter hardy. It is especially recommended for newly installed roses until you see how they perform for you.
If your roses or broadleaf evergreens are in an exposed spot, or if you have recently transplanted them, it is wise to spray them in late fall with Wilt Pruf, an anti-desiccant spray made from pine sap. This will keep the plants from losing valuable moisture in the cold drying winter winds. Be sure your broadleaf evergreens go into the winter well-watered as an added extra protective measure.
It is not necessary to remove all of the leaves from your garden beds in the fall. In fact, unless your leaves are thickly covering the crowns of your plants, LEAVE THEM! Leaves not only add nutrients and organic matter to the soil, they also support all sorts of life in your yard. Many creatures such as bees and wasps, wooly bear caterpillars, non-migrating butterflies and moths, spiders, snails, worms, frogs, lizards, and turtles overwinter in leaf litter.
Read this article by the Xerxes Society about this topic:
Consider your leaves as a valuable resource in your happy habitat. After raking thick layers of fallen leaves from your lawn, save them in a pile to use as mulch or allow them to decompose and form compost to enrich your garden beds. As leaf drop slows down and comes to an end, mulch the remaining leaves with your lawn mower. This will increase the organic matter and feed the soil, promoting a healthier lawn.
There are two different mulching chores in the fall.
1. If you have recently planted or transplanted your perennials or shrubs, mulch the soil around them immediately with leaves, shredded bark, or other organic mulch. This will keep the soil warm for a longer time and promote rooting well into late November. The longer plants root in, the happier they will be in the winter and the bigger they will be next spring!
2. AFTER THE GROUND HAS FROZEN (usually not until mid to late December in Connecticut) lay cut evergreen boughs over the entire garden, crowns and all. Apply this loosely, no more than an inch thick. The purpose of the winter mulch is to KEEP THE GROUND FROZEN!!!! This will then prevent the alternate freezing and thawing of the soil which causes the plants to heave up out of the ground, exposing their roots to the cold. Snow will also provide this protective blanket, but snow cover is not guaranteed in Connecticut! This is most important to do with newly installed gardens.
If you have had issues with diseases such as rust on hollyhocks or botrytis on peonies, do not compost or chop and drop this debris. Instead, bag it and discard it.
In an effort to provide horticultural information, these educational documents are written by Nancy DuBrule-Clemente and are the property of Natureworks Horticultural Services, LLC. You are granted permission to print/photocopy this educational information free of charge as long as you clearly show that these are Natureworks documents.