When to trim perennials?

Pinching, Pruning and Cutting Back Perennials

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Do your perennials intimidate you when they have stopped flowering? Do you suffer from “fear of pruning”? Are you afraid to chop back your plants because you think you will hurt them? You are not alone!

Late summer and fall can be a difficult time in the perennial garden. Anyone can have a lush, beautiful flower border in June. Books and magazines humble the average gardener with their pictures showing perfect displays of plants, ablaze with color, perfectly proportioned, layered from tall to short. Yet, when the “high summer” plants fade away, the garden often falls apart. The flowers of Campanulas, Shasta daisies, Delphiniums, and many more June bloomers fade away by late July or early August. Once their flower stalks have been removed, the remaining plant is unsightly and a LOT shorter than when it was in bloom. Other mainstays of the early border such as poppies and bleeding hearts go dormant and disappear, leaving enormous ugly gaps in the garden. Some plants, such as cranesbill geraniums or `Crater Lake’ Veronica, stay around but you almost wish they wouldn’t because they begin to look so tired and ragged that they detract, rather than add, to the beauty of the garden picture.

The average perennial blooms for three to four weeks. There are many perennials, however, that have the capacity to bloom continuously for two to three months, but only if they are deadheaded, cut back and fed in midsummer. Plants are put on this earth for the purpose of reproducing themselves. When a plant finishes blooming, it immediately starts to set seed. If a perennial has the capacity to continue blooming, you must remove the dead flowers (deadheading) and prevent seed pods from forming. The plant then gets the signal to flower again! Regular deadheading encourages repeat blooms as well as making the garden look fresh and neat.

Some perennials bloom heavily for 4-6 weeks and then will rebloom again in the fall if the entire plant is cut back hard and fed. This renewal pruning is a dramatic, often scary step for a new gardener but well worth the effort as it provides a two season bloom period.

If a plant blooms continually for many months or repeat blooms, it uses up a lot of energy. These plants must be fed in midsummer in order to give the plans the energy to continue performing at peak levels.

If you are going to have an attractive late garden, you must learn exactly what to expect from your plants AFTER they have finished blooming. By being brutally honest about their good and bad points, you will be able to realistically assess what they will contribute design-wise to the overall garden picture.

Let’s go into detail about exactly how to deal with perennials in mid summer. I took all of the methods that I use regularly and organized them into 12 categories. All perennials fit into at least one of these categories, some into more than one.

1. Cut the flower stalks to the base, deep within the crown.

Examples: Daylilies, Iris, Primula, Pulmonaria

This is perhaps the easiest type of deadheading to do. These plants have flowers at the end of long flower stalks. When the last flower has finished, the stalk should be removed to the base, deep within the crown of foliage. Do not leave a stub. Usually, these plants do not rebloom, but in the case of some daylilies (`Stella D’Oro’ is an example) regular deadheading once a week will prevent seed pod formation and stimulate the plants to produce more flowers. For plants that do not rebloom, the removal of the flower stalks stops seed production, giving more energy to the plant. This makes the foliage healthier AND makes the garden look neater.

2. Two step cutting back process.

Examples: Achillea, Leucanthemum (Shasta daisies), Salvia, Echinops

The plants in category two have leaves all along the flower stalks with flowers at the top. After flowering has finished, the first step is to cut the flowers off to the next good set of flower stalk leaves. In about 2-3 weeks, the leaves on flower stalks will start to look sickly. At this point, cut the entire flower stalk down to the base. Growing at the bottom of these flower stalks will be lush, green basal foliage. By removing the flower stalks, you give energy to this growth and it will increase in size and vigor for the rest of the season. Many perennials in category 2 will rebloom in the fall. Examples would be perennial salvias (Salvia nemerosa) and fernleaf yarrows (Achillea millefolium).

The biggest problem with this method of deadheading is what it does to your garden visually. Let’s say that you have a large clump of 3-4′ tall ‘Thomas Killen’ Shasta daisies in the center of your garden. When the flowers are done, and the flower stalks are finally cut to the basal foliage, this spot in your garden has gone from a dense mass of foliage and flowers 3-4′ tall to a 6″ clump of green leaves on the ground. This destroys any carefully planned layering of heights in the garden. It is very important to KNOW that this is going to happen and plan for it by placing plants next to or behind this Shasta daisy that will either bloom later in the season and/or will remain tall and bushy, offsetting the visual gap left by cutting back the Shasta daisy. The other design technique to consider is to not put too many of the type 2 plants together in one spot or you will be left with such a large gap later that it will be impossible to hide it. Instead, intersperse them with late bloomers or plants that don’t get cut to the ground (see # 4).

3. Continuously cut back the dead flowers to the next set of flower buds on the flower stalk or shrub; feed in midsummer to stimulate continued bloom.

Examples: Scabiosa `Butterfly Blue’, Knautia macedonica, Buddleia davidii (Butterfly Bush)

The plants in this category are long bloomers. The only thing stopping flower bud formation is seed formation. Therefore, week after week, the individual flowers are tediously cut back to the next flower buds. When there are no more flower buds, the branch is cut back to the next set of leaves.

When using type 3 plants in design, it is useful to know that they generally retain their bulk throughout the growing season. They can be counted on to fill the space allotted to them and not leave any enormous visual gaps.

4. Cut the flower heads off to a good set of leaves. Plants remain up and are bushy all season long, offering substance to the garden even after blooming.

Examples: Phlox paniculata, Eupatorium maculatum `Gateway’

This is a very easy category to take care of. These plants have flowers at the top of the plant. When they are finished blooming, you simply remove the flower down to the next good set of leaves (never leave a stub). The plant doesn’t die back, but instead remains bushy for the rest of the growing season.

Visually, this category of plants is very useful in garden design as it stays at just about the height that it was when blooming. You do not have to come up with any design tricks to fill in gaps. These plants are a steady and constant visual presence.

5. Wait until there are more seed pods than new flower buds & shear the plant back with hedge clippers.

Examples: Coreopsis verticillata `Moonbeam’, Linum perenne

These plants tend to produce lots and lots of small flowers. Deadheading them individually would be a tedious chore. Instead, wait until they are just about done blooming, when there are lots of seed pods and few flower buds. Using hedge clippers, sheer the plant back, removing 1/4 of the top growth. You may have to then do a little hand pruning to clean up any ugly stubs that remain.

These plants respond well to feeding after shearing. For example, Coreopsis `Moonbeam’ will often rebloom within 2-3 weeks after shearing if fed right away. Do this no later than early August.

6. Drastic Regenerative Pruning: Severely cut the plant back by 50% or more; feed; the plant will regrow a new crown of foliage and may rebloom within 2-3 weeks.

Examples: Cut back and won’t rebloom: Veronica teucrium ‘Crater Lake’, Artemesia `Silver Mound’

Cut back and will rebloom: Nepeta mussini (Catmint), Lamium maculatum

Shear back a plant after its initial heavy bloom period to encourage new growth and repeat blooms. Many perennials are long and repeat bloomers. After blooming heavily for 4-6-8 weeks, the plants become leggy, some of the older foliage may become unsightly or spotted, and there are many dead seed pods mixed in with the new buds and flowers. This technique takes courage. I often nickname it “cutting off the ponytail” as it seems as if you are removing a tremendous amount of the plant. I usually start by using a hedge clipper and shear the plant back by 1/3, ½ or even 2/3. I then clean up any stubs left by the shearing with my hand clippers. I foliar feed the plant and within 2-3 weeks, it will regrow a new head of foliage and begin blooming again.

7. Plants are summer dormant. Deadhead by any of the methods described above; foliage gradually goes dormant; cut to the ground when the leaves are yellow; some plants regrow new foliage later in the season.

Examples: Plants that go dormant and do not reappear: Mertensia virginica, Dicentra spectabilis, spring blooming bulbs,

plants that go dormant / foliage reappears in the fall (they do not rebloom), Papaver orientalis, Doronicum pardalianches

These plants create what I call “booby traps” in garden design. Because they eventually disappear, they leave big gaps in the garden. It is important to KNOW that this will happen, and arrange to have something else surrounding that empty spot that will bloom and/or have good leaves later in the summer and fall.

8. Self Cleaning Plants: Flowers fall off on their own and deadheading isn’t needed.

Examples: Dicentra eximea, Corydalis lutea, Campanula carpatica, Galium odoratum

What could be easier? These plant have flowers that are small and prolific. When they are finished, they fall off. The only drawback to these plants are that some of them self sow (Dicentra, Corydalis) because you are actually leaving the seed pods on, you just don’t notice them and they don’t sap energy from the plant by ripening.

9. Cleaning out the old, tired foliage

Examples: Large leaf Cranesbill Geraniums, Alchemilla mollis, Brunnera macrophylla

Tracy DiSabato-Aust, author of The Well-Tended Perennial Garden, calls this deadleafing.

This maintenance technique has to do with the appearance of the overall plant, rather that with the flowers or seed pods. On these plants, the older leaves become tired and ragged. Once during the summer, remove 1/4-1/3 of the oldest, yellowest leaves to the base, opening up the crown of the plant and encouraging fresh new foliage to grow. This will keep the plant looking fresh for the rest of the growing season.

10. Don’t deadhead! Plant either self sows or has attractive seed pods that can be harvested and used for dried flower arrangements.

Examples: Biennial foxgloves, Aquilegia (Columbine), Belamcanda (Blackberry Lily)

Biennials reproduce themselves by setting and spreading seed. If you deadhead them, you will terminate their reproductive cycle and will have to replant them. Other perennials, such as columbines, are short lived plants. By allowing them to go to seed, you will encourage new stands of plants when the mother plant dies. Many perennials are grown for their decorative seed pods. An example is Belamcanda chinensis, the Blackberry Lily. This plant blooms in July and August with orange flowers. After blooming, the seed pods ripen and split open, revealing dark black berries which are attractive as dried flowers.

11. Liveheading: This is when you remove perfectly good flowers because you don’t like them or don’t want them!

Examples: Stachys lanata (Lamb’s Ears)

Not all flowers are attractive, and many plants are grown for their leaves instead of their flowers. Never feel guilty if you want to remove a plant’s flowers and just enjoy its leaves.

12. Don’t do anything until the following spring.

Example: Ornamental Grasses

Ornamental grasses bloom in the late summer and fall. They are left alone to provide winter interest in the garden and are cut to the ground in late winter or early spring.

These twelve categories give you a battle plan for taking care of your garden. Remember that some plants may demand more than one method. If you are not sure which category a specific perennial fits into, observe it for one entire growing season. Experiment with it and record your results. Eventually, you will become comfortable with your plants and it will become second nature to cut them back and groom them on a regular basis. If you use these methods, your gardens will look fresh and attractive from spring until fall.

CUTTING BACK PLANTS

1. Cutting back to manipulate the bloom time.

When you cut back a plant, you set back its bloom time by about 2-3 weeks. Cutting back early in the season has a mild effect. Cutting back in July has a much stronger effect.

a. Vacation cutting back – If you know that a plant will bloom when you will be away on vacation, you can manipulate its bloom time by cutting the entire plant back. An example is perennial hibiscus, which normally blooms in August. If you cut this plant back by 1/3 – ½ in early July, you will create a shorter, branched plant that will not begin flowering until two to three weeks later than its normal bloom time. i.e. the very end of August or the beginning of September. Thus, when you return from vacation after Labor Day, your plant will just be starting its peak bloom time.

b. Cutting back to achieve peak bloom for a party, wedding or garden tour. Use the same concept described above to time blooming of perennials for special events. For example, if you are planning a September wedding in your garden, you can purposely cut back your late July and August bloomers hard in late June or early July. Then, these will bloom in tandem with your regular September bloomers.

c. Pinching or cutting back in stages to prolong the bloom time (double or triple it) and to hide the unsightly part of the plant after blooming. This is one of the most exciting advanced maintenance techniques a gardener can learn. The concept is to create a layered effect. The back ½ of the plant is left alone to grow to its normal height and bloom at its normal time. The front half of the plant is cut back by 1/3-1/2 in late May or June, at the latest early July. The exact time of cutting back depends upon how quickly the plant grows and what time during the summer or fall a plant blooms. Early bloomers such as Leucanthemum (Shasta daisies) are cut back in Southern Connecticut in late May or very early June as the growth is elongating but before the buds are setting. Late bloomers such as Chelone lyonii ‘Hot Lips’ (Turtlehead) can have the front half of the plant cut back as late as early July. The result is that the back of the plant blooms first at its normal time. The front (pinched or cut back) half of the plant then begins to bloom 2-3 weeks later. As the back half is finished, it can be deadheaded, it will be hidden by the blooming front half. This doubles the bloom time and serves to detract the eye from the dying flowers and declining foliage of the back half of the plant.

  • This technique can be applied to a plant in three stages as well, which will triple your bloom time.
  • You can also take a large drift of one variety of perennials and cut back various sections at two week intervals, then manipulating and spreading out the bloom time for many more weeks wherever you desire.
  • If you discover that you have created jarring color combinations, this technique can be used to delay blooming of one of the two plants and thus prevent clashing colors!
  • This can be done with MANY perennials. Some of my favorites to use this technique on are: Monarda, Leucanthemum, taller Veronicas, Chelone, Hibiscus, Asters, Echinacea, Helenium, Heliopsis, Nepeta siberica, Nepeta subsessilis, Physostegia, Platycodon.

2. Cutting back the front of a plant to staggered heights to clothe the plant with attractive foliage all the way to the ground.

Some perennials, by the time they bloom, have “ugly legs”, i.e. they loose the lower leaves or the lower leaves become unsightly. Therefore, when you view them the flowers are pretty but the foliage detracts. By cutting the front of a plant in stages, you can create a stepped or layered effect to the front foliage of the plant, hiding the ugly legs. Try cutting the very front to 6”, the next level to 8-12”, the next level 15-20”, etc.

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.

To Cut Back or Not to Cut Back?

Generally, you do want to cut back your plants prior to the next spring — but there are some exceptions. Here are some dos and don’ts to ensure healthy, thriving plants next season.

DO cut them back if…

Image zoom When lilies start to die back, you can cut them.

You’ve just had a frost, and the plant is starting to die back: Wait until after the first frost to cut plants back. Cut them about 3 to 4 inches from the ground so you can easily see where your plant is next spring. Feel free to compost the cuttings.

Image zoom Peonies often get hit with disease. If they are showing brown spots, throw away the cuttings.

The plant is diseased: Cut it back the same way as you would other perennials, but throw out the cuttings. Mixing diseased leaves into compost can infect other plants!

DON’T cut them back if…

Image zoom Grasses (like the zebra grass shown here) are insulated when snow falls.

The plant is a grass variety: Grasses add visual interest throughout fall and winter. They also collect snow around their bases, which provides insulation for the plant.

Image zoom Aster seeds attract finches during the winter.

You want to attract wildlife: You can also leave plants alone to attract birds and other creatures to your yard throughout winter.

We gardeners tend to be creatures of habit. For years I headed out in fall to prepare my garden beds for winter. Pruners in hand, I attacked almost all my perennials, cutting them nearly to the ground as gardening books at the time said to do. Then along came Tracy DiSabato-Aust, with her book The Well-Tended Perennial Garden – Planting & Pruning Techniques. Her wealth of knowledge jumps at you from every page. This acknowledged “Queen of Pruning” shares her observations, giving us all the benefit of her own experience.

I had no idea just how many plants would benefit from being left alone in fall and tidied up only after they put in their appearance when winter was over. In this book we learn not only when or when not to prune individual perennial species and cultivars but also why or why not.

The author reminds us that some foliage left unpruned in fall may provide winter shelter to some bird species. In addition she explains that ornamental value and winter interest can come, not only from the conifers and shrubs that are always left standing, but also from perennial seedheads (many provide food for different bird species), stem colour, evergreen foliage and even the basic structure and form of the perennials left upright in a garden over the winter months.

* Watch for the animated hummingbird and butterfly with the plants that attract them. *
The deer icon indicates plants that deer are not usually attracted to.The best time and method to propagate plants can be found on our image-intensive PROPAGATION page. To help your plants grow their best, check out our FERTILIZATION page. To create your own plant partnerships based on tried and true color theory, check out our GARDEN COLOR page. To see if a particular plant is on this page press Ctrl+F, type in the name, then click the Find button.
NO FALL PRUNING RECOMMENDED & WHY Break your old habits and leave the following plants unpruned or pruned back only to basal foliage for the winter. After all, who wouldn’t follow advice that reduces the fall work load in the garden, provides winter interest and shelters and feeds many different birds! If you’re afraid you’ll cut back plants that should be left alone just do as I do. Insert short garden stakes in front of these clumps to avoid pruning them back accidentally. Once everything else has been done the stakes can be removed and stored away. Acanthus: Bear’s Breeches

  • finished bloom spikes may be cut off at the base
  • cut off any old foliage that collapses to the outside of the plant by late summer
  • leave new basal foliage over winter
  • cut off damaged foliage in the spring

Aconitum: Monkshood

  • cut back to any new basal foliage after flowering has finished
  • leave this basal foliage over winter and cut off in spring

Ajuga: Bugleweed

  • plants are evergreen
  • do not prune foliage for winter
  • may need only dead-leafing in spring

Anaphalis: Pearly Everlasting

  • do not prune in fall for the winter
  • cut plant back only in the spring

Anthemis: Golden Marguerite

  • plants should be cut back to new evergreen basal foliage after flowering by late summer
  • leave this basal growth for the winter
  • prune off only damaged growth in spring

Arabis: Rockcress

  • plants should be cut back and shaped immediately after flowering
  • do no more pruning prior to winter
  • clean up any dead foliage in spring

Armeria: Thrift

  • remove deadheads and stalks after bloom to basal foliage
  • this plant is evergreen so no fall pruning should be done
  • remove winter damage in spring

Artemisia: Artemisia, Mugwort

  • do not cut back into old woody sections at any time
  • plants can be shaped and cut back early in the season
  • do no pruning after August

Arum: Arum

  • this plant is evergreen so should not be cut down in autumn
  • simply dead-leafing in spring will remove untidy foliage

Asarum europaeum: European Wild Ginger

  • plant is evergreen to semi-evergreen and requires no fall pruning

Asclepias: Butterfly Weed

  • do not cut back in autumn

Astilbe: Astilbe

  • performs best if not pruned back in fall

Astrantia: Masterwort

  • cut stems to basal foliage after flowering is finished
  • leave basal foliage intact until spring

Aubrieta: False Rockcress

  • this plant is evergreen
  • pruning may be done at stages during summer
  • do no pruning after mid-summer

Aurinia saxatilis: Basket-of-Gold

  • evergreen or semi-evergreen
  • leave intact over winter

Bergenia: Bergenia, Pigsqueak

Buddleia: Butterfly Bush

  • this is a shrub that should not be cut back until spring

Digitalis: Foxglove

  • new basal foliage may appear during summer
  • after blooming is finished, cut plants back only to this basal foliage
  • dead foliage can be removed in spring

Echinops: Globe Thistle

  • cut back to basal foliage after bloom
  • if rebloom occurs cut back stems to basal foliage
  • leave over winter and tidy up in spring

Epimedium: Barrenwort

  • this plant is semi-evergreen
  • leave foliage for winter interest
  • cut back unsightly old foliage in very early spring

Eryngium: Sea Holly

  • deadhead back to basal foliage which remains evergreen
  • leave for winter and prune in spring

Euphorbia: Spurge

  • shear back and shape plants immediately after flowering, to prevent excessive seeding
  • clean up foliage in spring

Gaillardia: Blanket Flower

  • cut flowering stems to basal foliage in late August-early September
  • preventing further blooming helps the plant’s survival chances
  • any new basal foliage that appears should be left until spring

Geum: Avens, Geum

  • this plant is semi-evergreen
  • cut stems to ground after flowering finishes
  • cut foliage back only to new basal growth
  • reserve full cut back until spring

Helianthemum: Sun Rose, Rock Rose

  • an evergreen sub-shrub
  • do not prune after late August
  • plants may need only a very light trim in early spring

Heuchera: Coral Bells

  • older top growth can be cut off in late summer
  • this may reveal better foliage underneath
  • do not prune further for winter
  • remove winter-damaged foliage in spring

Hypericum calycinum: St. Johnswort

  • plants are evergreen to semi-evergreen (depending on climate)
  • shear in early spring to remove winter damage

Iberis: Evergreen Candytuft

  • this plant’s foliage is evergreen
  • cut back only immediately after flowering
  • any winter damage can be removed in spring

Kniphofia: Red-Hot Poker

  • cut old flower spikes to the ground after bloom
  • cut foliage back at the same time by no more than half
  • in fall tie foliage over the top of the clump for winter protection

Lamium: Dead Nettle

  • cut back to basal foliage in mid-summer
  • winter damage should be minimal

Lavandula: Lavender

  • remove old flowering stems after bloom
  • do not prune after late August
  • remove tips that sustain winter damage after new growth has appeared in spring

Limonium: Sea Lavender

  • foliage is evergreen to semi-evergreen
  • do not prune for winter

Liriope: Creeping Lilyturf

  • foliage remains evergreen into early winter
  • shear to ground in spring to encourage new growth

Lupinus: Lupine

  • cut back to new basal foliage in July
  • do no further cutting back until spring

Lychnis:

  • this plant is a biennial
  • cut stems to basal foliage after bloom
  • silvery-grey foliage stays nice into winter
  • cut off winter-damaged foliage in spring

Nepeta x faassenii: Catmint

  • prune only immediately after flowering
  • you may cut back after several killing frosts or leave foliage until spring

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