Fall is a glorious time of year to work in the garden. It is the ideal time to take stock of your perennial gardens and correct mistakes and problem areas, dig up, rearrange and divide existing plants, add new perennials and shrubs, and plant spring blooming bulbs. 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 middle of October and continues right up until the ground freezes which in Southern Connecticut usually between Thanksgiving and Christmas.
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. For example, as I write this (in mid-October) we have already had three severe freezes. The tender annuals are history. The cold hardy annuals such as Calendulas are still gorgeous. The perennial Begonias, Hostas, and Hibiscus have already changed color and are being cut down this week. Some plants, such as the Filipendula rubra venusta `Magnifica’ was cut back two weeks ago as it had turned brown. It was done for the season. The Buddleias are still green, gorgeous and blooming their heads off! At least 75% of the remaining perennials in our gardens still have good foliage and I wouldn’t even dream of cutting them down yet. So, every few days, I go through the borders, shears in my pocket, 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 haven’t started blooming yet!!!!Some plants are also reblooming beautifully. You should see the Nepeta mussini in the rock garden, as well as the roses. They think it’s spring again! 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!
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. You cut them back all the way to the ground, and nothing is left but stubs. For instance, with Hibiscus you can cut it back to 6 inches above ground so you can tell where it is planted. Sprinkle seeds from pod around. These plants should be marked very well with permanent metal markers! Plastic labels will simply disappear or break over the winter. Examples are Peonies, Hostas, and perennial Hibiscus.
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 this 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, Salvias, Penstemons, and Scabiosas.
3. Plants that Remain UP into the Winter
A lot 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 mussini (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 falls into this category but they require special treatment. Even though their leaves 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. Despite THE RULE, cut these down at that late date even if they are green! 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. All other Irises are cut back when they naturally turn yellow.
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, and Perovskia as well as the flowering perennials Helianthemum (Sun Rose) and Chrysanthemum nipponicum (Montauk Daisy) fall into this category. Because they are above ground and exposed to cold drying winds all winter long, if these plants are planted in an open windy spot I will protect them with a cage of evergreen boughs. Just before the ground freezes, I jam cut evergreen branches into the ground around the plants. This keeps the wind off of them. In the spring, I cut these plants back to about 12″ and shape them. If you cut them back hard in the fall, and then they die back, you may end up with no plant at all! That is why I wait and leave them up.
C. Iberis (Candytuft) and Hellebores are early spring bloomers that are evergreen all winter long. I DO NOT CUT THEM BACK IN THE FALL AND I DO NOT CUT BACK in the early spring! Instead, I cut them back after blooming in late spring and early summer. They are evergreen and their flower buds are set on the plants in the fall. To protect them, I loosely lay evergreen boughs or salt marsh hay over the entire plants. In late winter, I chip away the snow and ice and expose the Hellebores as they can bloom as early as late February or March. I remove the protective covering from the Candytuft in late March as it is an April bloomer.
D. Bergenia and Liriope are also evergreens. Their leaves remain up all winter long. Their buds, however, are not set the fall before. In the spring, I sheer the Liriope to the ground and I clean off the unsightly leaves of the Bergenias to the base.
If you suspect that a plant is evergreen in your garden and it’s
leaves look terrific in December, leave it alone. It can add
winter interest to otherwise barren borders!
E. 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.
F. 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 twistems or twine. This keeps water out of the crown. In the spring, cut the foliage back to the base.
Flowering shrubs fall into two basic categories:
A. 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 and Lilacs.
B. 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.
*Caryopteris and Buddleias (Butterfly Bushes) should be left alone in the fall. The only thing I do is cut the long, wild shoots of the Buddleias so they don’t rock in the wind. I shape the Caryopteris slightly, cutting off the seedpods so they won’t self-sow. They add some structure to the winter garden. In the spring, I cut them back hard.
C. Hydrangea is 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. They bloom off of last year’s wood and are only hardy to zone 6. Even though they look pretty dead by November, leave them alone! ‘Annabelle’ Hydrangeas (H. arborescens) and P.G. Hydrangeas (the tree Hydrangeas) are hardy to zone 3 and bloom off of current year’s wood. They are left up all winter and cut back hard in the spring.
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 THE SOIL 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 of soil will still be alive in the spring. This is not necessary for Rugosa roses and their hybrids as they are very hardy.
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 Wiltpruf, 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.
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 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!), apply a winter mulch of salt marsh hay (which does not contain weed seeds) or 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 you and I both know that snow cover is not guaranteed in Connecticut!
Why bother with all this work, just when you are getting sick and tired of working in the garden at all? Garden sanitation is the answer. If you leave all the plant debris in the garden all winter long, you are also leaving lots of insect egg cases and disease spores. If you compost them, a hot compost pile will kill off the pathogens and convert the garden debris to a usable fertilizer. Layer your garden clippings with your fall leaves. Add manure if possible to heat it up. Create mega-compost piles that will pay you back generously in years to come. Don’t throw this vegetation away! RECYCLE IT!!!
Besides, it just looks so much better to stare out at a neat, properly cut back, tidy garden in the winter. Come the spring, when you have so much work to do, you will be glad that your garden is clean and ready for a new season.
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.