How to keep ornamental grasses looking smart in winter, by gardening expert Helen Yemm

Helen Yemm
·6-min read
A frosty winter's morning on the rock garden in John Massey's garden. Stipa tenuissima in the foreground. - Jonathan Buckley / gapphotos.com
A frosty winter's morning on the rock garden in John Massey's garden. Stipa tenuissima in the foreground. - Jonathan Buckley / gapphotos.com

Every week, Telegraph gardening expert Helen Yemm gives tips and advice on all your gardening problems whether at home or on the allotment. If you have a question, see below for how to contact her.

Gardeners of my acquaintance (and, dear readers, that includes many of you who tell me a lot about your gardening habits), seem in the main not to have gone mad for dramatic, wafty grasses.

However, we dabble, as often as not starting with strategically placed dramatic singletons as “punctuation marks” in traditional borders. Now, as the new year reveals, many such grasses are starting to look a little weather-weary and it may be a good time to air a few maintenance basics.

Botanists/gardeners have handily put ornamental grasses into two groups, governed, presumably, by their climatic origins.

Cool season grasses

This group includes the popular stipas, deschampsias and festucas. They start producing a subtle amount of new growth early in the year to flower in high summer, many of them remaining more or less evergreen.

  • To maintain their looks and lengthen their lives give them a thorough grooming session and trim in spring and perhaps an extra spruce-up in late summer if they start looking ratty.

  • This treatment suits them better than a radical early-season annual cut back (from which older plants in this group don’t recover easily).

  •  Use gloved hands or a small metal shrub rake, palms or tines facing upwards, to comb through clumps, teasing out the previous season’s beige remains.

  •  The best time to lift, divide or replace cool season grasses is shortly upon us: late winter or early spring. It is worth noting, at this point, that grasses do not need rich soil or fertiliser, and that many grow well in containers.

  •  Some members of this group self-seed generously if allowed to do so – notoriously the peroxide blond Stipa tenuissima and auburn pheasant tail grass, aka Stipa arundinacea now renamed Anemanthele lessoniana – I know, I know, annoying.

  •  The upside to the self-seeding is an easy supply of youthful replacements for exhausted parent plants.

Warm season grasses

Unlike the first group, warm season grasses (e.g. arundo, cortaderia, imperata, miscanthus, panicum, pennisetum and phalaris) start growing later and should not be divided or planted until late spring, when they are in active growth.

Their great annual cutting-down session (to a few centimetres from the ground) can take place once these grasses no longer make a pleasing autumn/winter “statement”, but (importantly) well before they start to produce their new base growth, which could easily get damaged in the fray. So check before you start carefully cutting them in early to mid-spring.

Tying clumps around their waists with twine before shearing them off at the ankles (for which one-handed Jakoti shears are the perfect gadget) ensures far less tidying up afterwards.

Design tips

Finally, where do you start with placing grasses – deciding what will be good where and with what, given that it is almost impossible to buy potted grass plants that give any clue as to their eventual stature, form, and allure?

Summer research on the hoof is essential And I can recommend Designing with Grasses by Neil Lucas (Timber Press) of Knoll Gardens nursery in Dorset. Also, Nancy J Ondra’s book, Grasses – Versatile Partners for Uncommon Garden Design (Storey Books), despite being written by an American for North American gardeners, describes and illustrates some inspiring combinations.

Tip for bulbs in late winter

Sprouted daffodils can still be moved - Diyana Dimitrova / Getty
Sprouted daffodils can still be moved - Diyana Dimitrova / Getty

It is still possible to make last-minute “adjustments” to spring bulbs. Daffodils are now putting their noses above the ground and some of them (those you forgot to move last year?) may be in the wrong place.

Now, as they have made their roots but before they start their big spring sprint, is the time to take action. Carefully trowel them up with a chunky protective clod of damp soil and transfer them, grouped together, perhaps, to a more suitable place. They may flower a week or so later than usual, but how much better is this than the fiddle of relocating them later when floppy-leafed and fading? Or forgetting to do so yet again.

Shrubs for sunny pots

My husband and I have recently moved to a retirement village, and now have a lovely, large south-facing patio on which to grow plants in containers (currently we have winter and spring-flowering sarcococca and rhododendrons). Can you suggest sizeable summer-flowering shrubs (that don’t mind being somewhat “cooked”) to grow in two additional, currently empty, square 50cm (HxWxD) containers?

– Margaret Culyer, via email

I presume that this patio is adjacent to your building and, as is very common even when ostensibly “south-facing”, is partly in shade, for which the rhododendron and sarcococca are well suited, with the other half in full sun. I think the overall harmony of the space would be maintained if you were to stick with “Mediterranean” evergreens for your two sunny containers, and I can recommend both a rosemary and one of the more compact and dense cistuses.

A tall, slim and shapely pale blue rosemary (e.g., ‘Miss Jessopp’s Upright’) would work, but more fun might be a bulkier variety with striking dark blue flowers such as ‘Tuscan Blue’, or semi-prostrate ‘Blue Lagoon’.

The smaller, lax-but-tidy cistuses include C. x corbariensis (pink buds that open to a mass of small white midsummer flowers). C. creticus (bright pink flowers) would also work well.

Use a loam-based compost with a little added grit. These shrubs flower best if kept on fairly lean rations.

Lichen on azaleas

I have a problem with a couple of azaleas that have developed lichen on their branches. This has meant that last May/June they produced very few flowers, and the foliage became sparse. Is there something that I can treat them with? We garden on acid greensand and the bed is north-facing.

– Gilly Crossley, via email

Azalea 'Nico' - Derek Croucher / Alamy
Azalea 'Nico' - Derek Croucher / Alamy

Lichens are complex life forms, part fungi, part algae, that colonise (mainly via airborne spores) anything suitably immobile: fences, rocks, and paving slabs, as well as the bark of trees and shrubs, homing in on those like your azaleas, that are by nature slow-growing shade-lovers.

“Treatment” of your shrubs is neither necessary nor in fact possible, so your best course of action is to improve their vigour by pepping up your soil.

In the next few weeks, in suitable weather, ensure that the soil surface in the bed is weed-free (beds of azaleas are too often overlooked, in my experience).

Follow this by forking it over lightly to de-compact it, before applying a granular feed suitable for ericaceous plants around the base of each shrub.

Then, give it a general mulch of moisture-retaining organic matter (avoid using animal manure or mushroom compost, which contains lime).

Aim to do this every year. The shrubs will hopefully spring into life and become leafier this coming year, and flower better the next.

GET IN CONTACT | Do you have a question for Helen Yemm?
GET IN CONTACT | Do you have a question for Helen Yemm?