Step away from the secateurs!
Just itching to cut back fading perennials? Well here’s why you’re making a mistake
DIG deep into old gardening books and you’ll sometimes come across a nugget of wisdom that still has a place in today’s gardens. Yet a lot of the musty information sandwiched between faded covers is so hopelessly outdated that following it would do more harm than good.
One such piece of moth-eaten advice that deserves to be confined to history is tidying up herbaceous borders by chopping everything back hard in autumn. In fact, in an hour or so browsing the shelves of the gardening section of a local second-hand bookstore, I didn’t find a single encyclopaedia, monthly guide or almanac published during the 20th Century that wavered from suggesting this as the best course of action.
Not one mentioned leaving perennials with robust stems and sound seed heads. Old habits die hard, and some gardeners continue to trim everything in beds and borders with enthusiasm. In my opinion, it’s much better to take itchy fingers off the secateurs by adopting a more measured approach to border maintenance, and only pruning back perennials if necessary.
There are many reasons why it’s a good idea to leave seed heads for as long as possible. The most obvious one is that seed heads look fabulous, in a shabby chic sort of way. And a multitude of dried stems in different shapes and sizes will help to provide some sculptural interest in gardens when there’s very little else going on.
The golden remains of Phlomis russeliana, achillea, fennel, sedum, cardoon, angelica and a host of other perennials will give your garden a lift when backlit by low sun late in the season. After a cold snap, they really dazzle when coated in a sugary hoar frost.
Deciduous grasses are of special value as their foliage, stems and feathery seed heads add structure, texture and colour to the winter scene. Apart from providing visual interest, they add movement and a rustling sound as they sway in the breeze. Among the best ornamental grasses for late interest are Panicum virgatum ‘Heavy Metal’, Calamagrostis x acutiflora ‘Karl Foerster’ and Pennisetum alopecuroides ‘Hameln’, along with a host of different miscanthus.
It’s not all about aesthetics. Penstemon, gaura and other perennials with a woody branch structure are only borderline hardy in parts of the country. The top growth is best left in place to protect the crown when temperatures drop. Damaged shoots can be pruned back to healthy buds in spring.
Some perennials and grasses are best left standing for winter wildlife. A wide range of birds will eat seeds from the old flower heads, while insects will hibernate in hollow stems, under leaves and inside seed heads. I’ve even seen ladybirds hunkering down in the fluffy plumes of miscanthus grasses. Of course, not all dead stems are worth keeping. I’ve al r e a dy r e moved t hose from astilbes and Crocosmia ‘George Davison’ as they really aren’t that ornate, and I have just cut back some massive agapanthus st ems because they were flopping horribly across a bed following a stormy spell earlier in the month.
Lady’s mantle, hostas, hardy Frost adds beauty to a faded cardoon seed head geraniums and astrantia and similar clumpforming perennials don’t possess any ornamental value once the weather takes a turn for the worse, so take the opportunity to tidy them up before winter. Prune other perennials as required to keep borders in good shape. Eryngium, sedum, Achillea fillipendula and a host of others are robust enough to make it to the end of winter intact. All deciduous grasses are best left untouched until early spring.