Cutting back perennials: balancing winter interest and plant care

Jump to: Winter interest · Spring cutting back and mulching · Gaura and Penstemon · Wind-rock · Diseased material · Kniphofia and Disporopsis · Tools · Learning through observation

As autumn progresses, it can be tempting to tidy the borders and cut everything neatly to the ground. But a perennial border does not need to be put to bed quite so thoroughly. For many plants, leaving the old growth in place until spring is the better approach.

Standing stems, seedheads and fading foliage give the garden structure through winter. They also provide shelter for insects and other wildlife, while the old growth can help protect the crown of the plant from the worst of the weather. 

Getting to know how your plants grow is one of the most useful ways to learn how to care for them. Watch what happens as the seasons change: which plants die back completely, which keep their leaves, and whether fresh shoots appear from below ground, at the crown or along existing stems. These observations will tell you a great deal about what to leave alone, what to remove and when.

The important thing is to look at the plant in front of you, rather than treating the whole border in the same way. Some perennials can be cut back as new growth begins in early spring. Others need their tops for longer, and some should never receive an all-over haircut.

Leave something for winter

A border still has plenty to offer after its flowers have faded. The tiered seedheads of Phlomis russeliana and Phlomoides tuberosa ‘Amazone’, the broad flowerheads of Hylotelephium, the dark seedpods of Baptisia and the seedheads of Actaea and Eryngium (sea holly) all bring interest beyond the flowering season. The upright stems of Chelone (turtlehead) and the changing colours and movement of ornamental grasses add to the winter picture. Frost picks out their outlines, and low winter sunlight brings a different quality to familiar plants.

Chelone seedheads provide winter interest and seed for the birds.

Where stems remain upright and healthy, there is often no need to remove them simply because they have turned brown. Leaving them also retains small sheltered spaces where insects can overwinter.

Leaving healthy old growth in place also more closely follows what happens in the wild. As the foliage dies back and falls to the ground, it forms a natural mulch around the plant. 

One observation we have made at the nursery is that Phlox paniculata performs much better when left with at least 20cm of top growth over winter. Allowing its old stems to stand is a positive part of caring for the plant, rather than simply a job postponed until spring.

There is a balance to strike. A stem that has collapsed across a path can be removed, and a heavy, sodden mass of foliage need not be left smothering neighbouring plants. Selective tidying is quite different from clearing the whole border.

Miscanthus seedheads glowing in the low sunlight.

When to cut back in spring

For many herbaceous perennials, the appearance of fresh shoots at the base is a useful signal that it is time to remove the previous year’s growth. Work around those new shoots carefully, cutting away the dead stems without damaging the emerging leaves.

The crown is the point where the shoots and roots meet, usually at or near soil level. Do not cut blindly through the centre of the clump: part the old growth first so that you can see what you are doing.

There is no single date that suits every garden. A sheltered border may be well ahead of an exposed one, and a cold spring can delay growth. Let the condition of the plants and the weather guide you, rather than the calendar alone.

Ornamental grasses need a little more thought. Deciduous grasses can have their dead growth removed before the new leaves become entangled in it. Evergreen grasses should not automatically be treated in the same way; many need only careful removal of dead material.

Once you have finished cutting back, it is a good opportunity to mulch around your plants while access is easy and you can see where the new shoots are emerging. Apply the mulch around the clumps, keeping it clear of the crowns rather than burying them. We’ll cover mulching in more detail in a future Grower’s Notebook.

Leave Oenothera (Gaura) and Penstemon until later

Oenothera lindheimeri, still widely known as Gaura, and Penstemon need a more patient approach.

Leave their tops in place over winter rather than cutting them hard back in autumn. The old growth helps shelter the lower parts of the plant, and cutting back too early removes that protection while frosts are still a risk.

At Hardy’s, we leave the main cut-back until April or May, once the risk of frost has passed. In a colder or more exposed garden, that may mean waiting longer than in a sheltered spot.

Cut Gaura’s previous season’s stems back to around 5cm above ground level, taking care not to damage fresh shoots at the base. With Penstemon, shorten the old stems to just above healthy new shoots, usually around 10–15cm above ground level. 

Oenothera (Gaura) should not be cut back until after the last spring frosts.

Wind-rock on exposed sites

Wind-rock is commonly associated with newly planted trees and shrubs, particularly roses, but some herbaceous perennials can also be affected on exposed sites. As the wind catches tall or excessive top growth, the plant can rock backwards and forwards, putting strain on its roots and loosening the soil around its base. This can leave a gap around the crown where water collects, increasing the risk of rot. Newly planted perennials are particularly vulnerable because their roots have not yet firmly anchored them in the soil.

Where plants such as Oenothera (Gaura) and Penstemon have excessive top growth, reduce their height by about a third to lessen wind-rock, while retaining enough growth to provide winter protection. This is a light autumn reduction, not the main spring cut-back.

The exception: diseased material

Leaving healthy growth through winter does not mean leaving everything.

Remove diseased stems and leaves when you find them rather than retaining them for winter interest or shelter. Keep this material separate from healthy garden waste and do not add it to your compost heap. Clean your tools before moving on to other plants.

Likewise, remove rotting material where it is sitting heavily over a crown. The aim is to retain useful protection, not a wet blanket that smothers the plant beneath it.

Not every perennial should be cut to the ground

Kniphofia, or red hot poker, is a good example of a plant that should not be given an all-over haircut. Keep its healthy leaves and remove dead foliage individually, easing it away where it comes free readily rather than pulling at firmly attached leaves. Spent flower stems can be cut out separately. This is selective maintenance, not an invitation to shorten the whole clump with shears.

Disporopsis pernyi also needs a considered approach. Its evergreen, arching stems are not simply dead herbaceous growth waiting to be cleared away. The previous season’s stems must be left in place until the fresh spring growth is almost fully established, rather than removed as soon as the first new shoots appear.

This is a lesson we learnt from our own mistakes. One autumn, we removed all the top growth to allow the new shoots to come through unhindered. The plants made almost no growth the following spring. What had seemed a helpful piece of tidying was anything but, and it gave us a much better understanding of how to care for this plant.

Kniphofia mustn't be cut down.

Tools for cutting back

At the nursery, we use our pointed fruit pruners for cutting back herbaceous material. They are lightweight and easy to use over a prolonged period, which makes a difference when working through a border. Most herbaceous material does not require anything more heavy-duty.

A little less tidying, a little more observation

Before reaching for the secateurs, ask whether the growth is dead or still living, whether it is providing winter structure or protection, and whether the plant needs a different approach.

The best guide is often the plant itself. Watching how it grows, dies back and starts into growth again will help you recognise the difference between dead material that can be removed and living growth that needs to stay. Over time, that understanding becomes far more useful than a fixed date in the diary.