As a gardener as well as a florist, I’ve learned to be wary of white. Flowers in this colour are what you might call ‘shouty’, sometimes at odds with their neighbours and difficult to position well, especially in the hard, harsh light of a hot summer’s day. Adding to the challenge is the fact that there’s not just one but many shades of white, from warm creamy white to grey-white and icy-white. They don’t always get along.

Put a cool white right next to a warm white, for example, and it will look instantly jarring. Using white flowers in any kind of vibrantly colourful planting plan has a similar visually disruptive effect, drawing the eye and creating a full stop when one often isn’t wanted. Even just one single small white flower in a sea of vivid colour packs a visual punch that’s well above its weight, the harsh contrast transforming it into an attention-hogger that demands to be noticed.

Instead, white flowers almost always look their best when combined with lots of interesting foliage plants in soft shades of green and grey, a lesson the noted English gardener Vita Sackville-West famously taught the world when she created her white garden at Sissinghurst.

An essay in restraint, Sackville-West used what she described as “a low sea of grey foliage” – species such as santolina, artemisia, stachys, Cineraria maritima, and Achillea ageratifolia – to anchor the planting and allow its more ephemeral blooms – white-flowering varieties of regal lilies, irises, peonies, foxgloves, delphiniums, the giant Arabian thistle Onopordum arabicum – to rise above it, so that they softly glowed rather than loudly shouted.

Skilfully used this way, white flowers can add magic and mystery to the tiniest of spaces, especially if you combine them with formal evergreen hedges and well-executed hard landscaping details such as elegant paths and paving. Unlike richer colours that tend to recede or even disappear in low light, they’ll bring a shady garden to vivid life in the similar way that they’ll add a luminous quality to the garden at twilight. For the very same reasons, white flowers come into their own at this time of year as the days shorten and natural light levels begin to fall.

In my own country garden, for example, an intentionally late sowing of white cosmos has produced plants that are only now getting into their stride. Planted in soft drifts into gaps in a sunny border, this hard-working, easy-to-grow annual will continue to bloom until the first harsh frosts so long as I keep it regularly deadheaded. With tall stems of pure white daisy-shaped flowers and feathery foliage, it also makes an excellent cut flower to bring indoors. Of the many varieties available, my favourite is the reliably abundant Cosmos ‘Fizzy White’.

Another white-flowering, autumn-blooming plant I wouldn’t be without is Gaura lindheimeri. Easily grown from seed, this ultra-resilient, drought-tolerant, sun-loving, exceptionally long-flowering perennial produces clouds of delicate white flowers flushed through with just a hint of blush for months on end and combines excellently with ornamental grasses and other modern-style perennial species such as sanguisorba and echinacea.

I grow a creamy-white flowering form of the latter in the same sunny border, propagated from seed sourced from Jelitto, the German seed company that carries a huge range of seeds of garden-worthy perennials. Slow to emerge in spring, echinacea can be a martyr to slugs and snails, but if you nurse it past this stage then its large, elegant, daisy-like flowers with their central boss of dark golden disc florets are both highly ornamental and very long lasting.

Another white flowering perennial that’s providing a great display in my garden despite this summer’s punishing drought is the white-flowering form of goat’s rue, Galega officinalis ‘Alba’. This plant’s dainty pea-like, clean white flowers and graceful foliage belie the fact that it’s as tough as old boots, as well as exceptionally easy to raise from seed. Shade tolerant, white goat’s rue also makes a great cut flower – yet another reason to love it. A tall perennial, it forms a large spreading clump, so make sure to give it space towards the back of a border to accommodate it.

Should I weed my garden in a heatwave?

That’s not the case for the dainty Mexican fleabane, Erigeron karvinskianus, an invaluable, semi-evergreen, drought-tolerant perennial which forms low clouds of its long-lasting miniature daisy-shaped flowers for many months. Different named varieties are available, including some with a slightly mawkish hint of blue or mauve. But the species itself is lovely as it is, with a multitude of white to very pale pink flowers and an ability to seed itself gracefully about the place without ever being unwelcome.

As for white-flowering shrubby species for the early autumn garden, you can’t go wrong with Hydrangea paniculata ‘Limelight’. Much more drought tolerant than its thirsty, mop-headed cousin Hydrangea macrophylla, this deciduous shrub’s large cone-shaped flowers emerge in a shade of pale lime green and then gradually change to a warm shade of creamy-white. Impressively long-lasting, these have a near-magical ability to partner well with almost anything – the reason why this hardy shrub is the backbone of so many garden designers’ planting schemes.

This week:

  • Check overwintering kinds of brassicas for signs of damage from the cabbage white butterfly, whose caterpillars can quickly strip the leaves. Handpick these off plants and smudge out any butterfly eggs found on the backs of the leaves, before netting the plants.
  • Unlike many other kinds of spring-flowering bulbs, daffodil bulbs are ideally planted in early autumn rather than later in the year as they need a long time in the ground for their slow-growing root systems to get established. Order and plant them this month if possible.

Dates for your diary

Claregalway Castle Annual Autumn Plant Fair: Claregalway Castle, Claregalway, Co Galway; Sunday, September 6th (11am-6pm). A host of rare-plant growers and specialist nurseries will be in attendance, plus crafts and local food stalls. See claregalwaycastle.ie and galwaytourism.ie.

Irish Seed Savers Association practical one-day workshop, An Introduction to Seed Saving: Capparoe, Scariff, Co Clare; Saturday, September 12th (10am-4.30pm; €100). See irishseedsavers.ie for booking details.

Plant Person Course: Hunting Brook Gardens, Lamb Hill, Tinode, Blessington, Co Wicklow; starts Monday, September 14th. This highly rated 10-month course takes place one day a month with expert gardener, educator, author, designer and plantaholic Jimi Blake, owner and creator of the gardens. Places limited. See huntingbrookgardens.com.