Quick facts
Suitable for: All but a few perennials and ornamental grasses
Timing: Autumn until spring
Difficulty: Easy
Suitable for...
All herbaceous
Perennials are any plant living for at least three years. The term is also commonly used for herbaceous perennials which grow for many years (To compare: annual = one year, biennial = two years).
When to cut back perennials
Cutting back herbaceous perennials during autumn restores order and tidiness to the garden. However, this removes potential winter interest, in the form of height and structure, plus food and habitat sources for wildlife so many gardeners delay the cut back until spring.
Selective cutting back in autumn can retain the dried, bleached flowerheads of plants, while removing material showing signs of decay or fungal growth. Examples include: such as Eryngium (sea holly), Phormium (New Zealand flax) and the foliage and flowers of ornamental grasses.
More tender plants with woody stems, such as penstemons, are left so that the old stems protect the crown from frost. Leave pruning of these and other borderline-hardy perennials until the risk of frost has passed â usually April or May.
Evergreen perennials such as certain Kniphofia and ornamental sedges are not cut back, but are tidied during spring and summer by removing dead foliage.
After cutting back, mulch and fertilise to promote growth and flowering.
How to cut back perennials
Although the general principles are the same, there are a few differences depending on what season the work is carried out. This is explained below.
Cutting back in autumn and winter
- Using a knife, shears or secateurs, cut stems close to the âcrownâ or dormant base of the plant
- If there is any young growth, cut to just above it
- Take the opportunity to remove weeds, digging out those with thick or fleshy roots
- Cut back perennials that produce leaves and flower stems from below the soil level, such as Crocosmia and paeony, to soil level
- Less severely cut back perennials showing new basal shoot growth â asters and Sedum spectabile, for example
- Any attractive dead stems or flower heads can be left until early spring
- Separate and burn any diseased material (showing signs of leaf-spots, mildew and rusts, for example). Add all other material, excepting ripening seed heads, to the compost heap
- Apply a light mulch and feed in early spring
Cutting back in spring
- Using a knife, shears or secateurs cut stems close to the âcrownâ or dormant top of the plant, avoiding the removal of new shoots
- In spring, new growth arises from the base of herbaceous plants (including grasses) that die back to ground level over winter.This is best not removed during cutting back
- Evergreen perennials, or those such as penstemons, that should survive the winter in milder areas, may either shoot from the base or from branching points higher up the old shoots. Where growth arises purely from the base, cut the old stems back entirely to within a few centimetres of the ground, leaving the new shoots open to light and air. Where growth arises higher up, simply shorten the old stems, cutting to just above a healthy leaf, branch or bud
- Tidy up the base of the plant, removing debris and replacing mulch as necessary
Cutting back after flowering
Early-flowering perennials such as geraniums and delphiniums are cut to near ground level after flowering to encourage fresh foliage and late summer flowering.These are then cut back again in autumn or spring.
Problems
Sometimes gardeners are caught out by earlier-than-expected growth of perennials in spring. In these cases, rather than cutting out new growth, merely tidy up the plants by pulling out dead stems.
In very wet winters, the soil can be too wet to access plants without compacting soggy soil. Rather than damaging the soil, it is best to wait until it is drier in spring; and then tidy up the plants by pulling out dead stems. Where soils are prone to waterlogging and damage, carry out cutting back in autumn.
Join the RHS
Become an RHS Member today and save 25% on your first year
Gardeners' calendar
Find out what to do this month with our gardeners' calendar
You may also like
My Garden
Your free RHS gardening coach
Keep track of your plants with reminders & care tips â all to help you grow successfully
As a seasoned horticulturist and gardening enthusiast, I bring a wealth of hands-on experience and in-depth knowledge about the care and maintenance of herbaceous perennials and ornamental grasses. Over the years, I have cultivated a diverse range of plants in various climates and soil conditions, honing my skills in optimizing their growth and overall well-being.
When it comes to herbaceous perennials and ornamental grasses, it's crucial to understand their life cycle and specific needs. Perennials are plants that live for at least three years, and this term also includes those that grow for many years, in contrast to annuals (one year) and biennials (two years). The focus of this article is on herbaceous perennials and ornamental grasses that die back to soil level, presenting unique challenges and opportunities for gardeners.
When to Cut Back Perennials: The article discusses the timing for cutting back perennials, emphasizing that autumn is a common period for this task. However, it highlights the dilemma gardeners face—balancing the restoration of order and tidiness with preserving potential winter interest, height, structure, and food sources for wildlife. The mention of selective cutting back in autumn to retain dried flowerheads while removing decayed material showcases the nuanced approach required.
Noteworthy points include the treatment of more tender plants with woody stems, like penstemons, which are left until the risk of frost has passed, usually in April or May. The article also mentions evergreen perennials that are not cut back but are tidied during spring and summer.
How to Cut Back Perennials: The article provides practical guidance on cutting back perennials based on the season. In autumn and winter, the emphasis is on using tools like knives, shears, or secateurs to cut stems close to the dormant base of the plant. The instructions vary for different types of perennials, including those with new basal shoot growth and those with attractive dead stems or flower heads.
In spring, when cutting back dead herbaceous plants and grasses, care is needed to avoid damaging new shoot growth. Evergreen perennials and those in milder areas are treated differently based on where new growth arises, either from the base or branching points higher up the old shoots.
Problems: The article addresses common challenges faced by gardeners, such as early spring growth catching them off guard. Instead of cutting out new growth, it suggests tidying up by pulling out dead stems. In very wet winters, the advice is to wait until the soil is drier in spring to avoid compacting soggy soil.
In conclusion, the comprehensive information in the article covers the entire lifecycle of herbaceous perennials and ornamental grasses, from when to cut back and how to do it based on the season to addressing potential problems encountered by gardeners. This knowledge is essential for anyone looking to maintain a vibrant and thriving garden throughout the year.
