How & when to prune herbaceous perennials
Lee Burkhill: Award Winning Designer & BBC 1's Garden Rescue Presenters Official Blog
Pruning herbaceous perennials is essential to make sure that year after year, you get beautiful blooms in your garden. However, it can confuse many gardeners as to when to prune and how.
However, most people struggle to know when or how to prune this plant group. With annuals, it is easy; at the end of the summer, you lift them and compost them, but with herbaceous perennials, there can be that awkward moment in Autumn when you're not sure what to do.
This guide gives you all my top tips for when and how to prune herbaceous perennials.
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Herbaceous perennials can be easily identified as this plant type, which will come back year after year, dying back each winter and regenerating each spring. They put on fresh green vegetative growth each year and then die back underground. Herbaceous plants usually have a root, bulb, corm or underground storage system that survives throughout the winter.
Herbaceous perennials don't require the care and attention of annuals or bedding plants, as the majority of them are fully hardy (there are exceptions, as with anything). This means herbaceous perennial plants will happily survive underground during the harsh winter frosts and arise again in the spring to dazzle us with their offerings.
The key to spotting a herbaceous perennial vs a shrub is that herbaceous plants don't put on woody growth in their stems like shrubs.
They are easy to spot as the first frosts of winter will turn them brown and crispy. Quite often, beginner gardeners think they are dead, but they are not.
Brown or dried-up herbaceous perennial plants in late autumn and winter are simply dormant.
They keep their energy underground in the crown and root system of the plant. Allowing the vegetative matter to die back once the plant has set seed in summer.
Two examples of a herbaceous perennial would be a Helenium which is your typical daisy-like flower, but then also a Banana plant (Musa basjoo) which, believe it or not, isn't a tree but a herbaceous perennial. The largest herbaceous perennial in the world, growing upwards of 3m each year and dying back!
The best time to prune herbaceous perennials is late winter in January to February.
Most gardeners have a habit of pruning herbaceous perennials at the end of Autumn. This occurs during the great garden tidy-up at the end of the season when gardeners are frantically trying to tidy up it seems. I'm not sure what it is with us Brits, but we do tend to love a good clean up and tidy.
What I find is that you may remove the dried-up stems of herbaceous plants to make the borders look tidier, but you're left with bare earth and spaces in your garden.
I advocate a different approach of pruning or tidying back herbaceous plants, like those in the Exploding Atom Garden, after winter around late February here in the UK.
Pruning in late Winter is far more beneficial, both visually and for wildlife. The reason for this is that herbaceous plants such as Salvia, Miscanthus, Geums and Foxgloves act as a really good food source for wildlife during the barren winter months.
Seed heads provide easy snacks, and other insects that take refuge around these plants help keep our wildlife alive during winter when food sources are scarce.
Secondly, the dried-up stature of these plants can look incredibly beautiful during the winter. Grasses with their light brown stems frozen in time and seed heads of taller herbaceous plants like Acanthus can extend interest in the garden.
Who wants to look at bare soil when you could be looking at arrangements of ghostly sepia-toned herbaceous plants?
Look at how interesting this is in the dead of winter. If it were bare earth, it would look barren. The grasses against the Carpinus tree and crisped-up Heleniums look wonderful and are great for wildlife in the garden.
When it comes to pruning herbaceous plants, it's important to have tools that are sharp, clean and suitable for the job.
Two tools are essential when pruning these plants back in winter.
If your secateurs are looking old, rusty or blunt, then follow my secateurs sharpening guide here. It's worthwhile spending 10 mins cleaning and sharpening them. It will save much time in the garden and protect your plants from awkward rough cuts of being torn at the base.
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Pruning herbaceous perennials is super easy. It's a case of cutting them back down to between 2 and 6 inches from the ground, depending on the size of the plant. For really tall grasses or Banana plants, 6 inches is enough. For a tiny Geum or Geranium, then 2 inches is sufficient.
Take a look at the flower bed below before pruning. See the grasses and other herbaceous perennials that have turned brown over the winter.
With a sharp pair of secateurs or a Japanese scyth, snip back old the old growth and compost it. See below how much has been removed and to what height. All neat clean cuts and the clippings have been composted.
To make it easy for beginner gardeners, I split herbaceous perennials into three main groups to help gardeners in knowing what and when to do. Even if you don't know the exact name of the plant you're dealing with this guide should help you to identify the pruning method required.
You're going to need sharp clean secateurs, gloves and a bucket.
Ground cover plants are relatively easy when it comes to maintenance. They tend not to look too messy as they are closer to the ground, so as they die back, they are pretty low maintenance. Needing very little pruning back. But sharp secateurs make easy work of cutting off the brown bits.
I cut ground cover herbaceous perennials back to 2 inches above the ground of 5-6cm. You can usually see a crown of green growth just above the soil level. So cut above this.
The issue you may find with ground cover plants is if there's a hard frost, the leaves can turn mushy and sometimes grow fungus. This is not good for plant health, so if this is the case, remove them in early winter. Stachys is an excellent example of a plant that needs an earlier prune.
If not, I always leave them and tidy them up at the end of winter just before spring.
Even plants seemingly surviving the winter need to be cut back to the ground. This is because the old growth will be weak, and you want the plant to send out vigorous new growth. So don't be tempted to try and salvage this group; be brutal, and you will be rewarded!
Group 2, the taller herbaceous perennials, is probably the most interesting, in my humble opinion, especially in winter. This group will keep the drama alive in your garden even during those dark miserable winter days. They are also more likely to have seed heads that provide sustenance for wildlife.
This is the group that most people seem eager to cut down at the end of Autumn. I call this group affectionately the 'Brown and Crispy Crew'.
However, I really do advocate that you leave the 'Brown & Crispy Crew' and see just how effective they are at keeping interest in your borders through the winter. You may even see small birds using them as perches or some insects working away on them throughout the winter.
Pruning this group is super easy, and I tend to prune these towards the end of February to ensure that any new early growth has a free run. With a clean, sharp pair of secateurs, you will cut down the 'brown and crispy crew' to just above ground level around 3 inches to 6 inches, 6cm to 12cm.
Some plants, like Penstemons, have delicate crowns, so you may want to leave these for another month or so. In the majority of the cases, though, a late February chop is fine.
Plants are tougher than you think, and it also allows you to plan the border for that year by seeing it without distraction. It also means you are able to look at your flower beds and identify any potential issues before the spring starts.
With sharp secateurs, cut this group back down to the ground - you can compost the cuttings.
This tall Salvia 'Blue Enigma' gets cut right back down to the ground.
This group is probably the easiest to deal with as all you're doing is a light tidy-up of any dead or damaged matter. Most of this category falls under ground cover, so any carpet-like plants that keep their colour through the winter or a large portion of the Ferns family fall into this group or anything with a glossy green leaf.
All you need to do is selectively remove any leaves or fronds in the case of ferns. Berginia only needs a light clear-up. Take out any old crispy leaves as they flower early in the season, so don't be too heavy-handed.
With evergreen grasses, like Stipa gigantea, lightly pull out any old spent flowers and use secateurs (with gloves as the leaves are sharp) to cut out any damaged leaves.
With Carex or Helictotrichon grasses, you can simply run your fingers through the grass and pull out any dead matter.
Evergreen herbaceous perennials only need a light tidy-up in later winter. Pruning should be light touch. Just nipping off with secateurs anything that is:
If you're a bit late in pruning your herbaceous plants, then my advice would be to still prune out all the dead material; however, don't go so far to the ground.
You want to avoid severing any new growth if you're pruning later in March or April. However, late pruning is always better than no pruning in my experience with herbaceous plants.
Yes, you can! All herbaceous clippings can be composted and should be reused and recycled in the garden. They make excellent woody material for compost bins, especially if you've got lots of green matter, such as grass clippings.
I've even used a shredder in wildlife gardens to cut down the herbaceous clippings and then use them as a mulch on the borders. Meaning nothing goes to waste or landfill.
If you haven't already considered creating a compost bin, I would urge you to read my speedy guide here. All gardens, no matter what size, can fit a small compost bin in to close the loop
The quick answer is not very often. Herbaceous perennials are tough plants, and whilst dormant, their roots, crowns and bulbs will be well protected from sub-zero weather. These plants are adept at surviving long winters and knowing the optimal time to pop back up in Spring.
If you're wondering if to hold off from pruning as there's going to be a frost again, my answer is not to worry too much. Pruning back old growth can't harm herbaceous plants. That's because the brown and crispy stuff is already dead.
Yes, it will give some protection from sinking frosts, but for the most part, you'll be fine pruning late winter, even if a March or April frost appears. These plants are tough.
If you're concerned about Penstemons and other more tender perennials, then why not layer your clippings on top of the crown until springtime? That way, you get the best of both worlds!
It's never too late to prune plants, but there is a best time vs the most difficult time. The best time to prune herbaceous perennials is late winter before the new growth. If, however, you're in April or May and you've still got last year's dead plant material still stuck to them, you can still prune this away.
The biggest problem with late pruning is you can't simply hack the plant back to the ground, as you'll cut off all the new growth in the process. You'll need to carefully remove the dead parts bit by bit with secateurs, not the Japanese scythe.
Absolutely you should! Leaving your herbaceous plants to crisp up during the winter is a vital food source for wildlife and offers protection. Beneficial insects will be overwintering in the leaf folds, seed heads and debris on the bottom of these plants.
Lacewings, ladybirds and other insects will be hibernating or overwintering, so cutting back herbaceous plants in Autumn makes it harder for them to survive.
Leaving herbaceous plants over winter also protects the soil. Acting as a protective fleece layer from extreme frost and also heavy rainfall. It stops the wind from scraping the soil's surface and is an all-around great protective layer.
By leaving the herbaceous plants through the winter, you also save yourself time at the end of a busy growing season. Putting off that work of pruning until the end of winter gives you, the gardener, much-needed time to relax!
Pruning herbaceous perennials late in the winter is the sensible option for you, the gardener and wildlife. By following this guide, you can easily prune back all plants, even if you don't know the exact name of them!
Do you have your own preferred pruning time or method for pruning herbaceous perennials? If so, I'd love to hear from you.
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Happy Gardening!
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Hi garden ninja I have a question on a few herbaceous perennials
The plants I have currently in the border (I intend hopefully to add some more)are coreopsis,osteospernums,salvias,lavandula, antirrhinum s, digitalis,calynopsis,campanula, dianthus,and senetti,I only planted these in the garden early last summer,so I avoided cutting them back in autumn is it alright now to go ahead and cut them back now late February?many thanks
Kind regards mark
Hi Mark,
Thanks for your comment. Yes, if you cut them back now that’s ideal before the new growth. Then they will be good to bloom this year! Happy pruning. Lee!