The window box could be considered the last bastion of the bedding plant. Public parks are at last relinquishing their impermanent blocks of double marigold and begonia in favour of perennial informality, yet the window box has seemingly escaped reform, hunkered on inaccessible ledges clutching armfuls of petunia.
Of course, there is good reason for this. With their shallow soil depth and exposed positions, window boxes require robust, low-maintenance plants, and traditional summer bedding has long fitted the bill. But these planters, however compact, are an opportunity for dynamic planting. They are rewarding spaces to garden in, particularly if you don’t have any outdoor space, and can provide a vital resource for wildlife.
Even in a modest-sized window box, there is room for successional blooms, evergreen structure and ephemeral sparkle, and there is a surprising number of attractive, hardworking plants that will contend just as well with it spacial and environmental constraints as a pelargonium. If that sounds like hard work, bear in mind that perennial plantings can remain in situ for many years, rather than being laboriously replenished each spring.
But the other incentive is an important one. Many traditional bedding plants – double-flowering begonias, marigolds and busy lizzies, for example – are much-hybridised annuals bred for vibrant colour but which offer little or no accessible nectar for insects. Amid an increasing biodiversity crisis, window boxes can prove genuinely invaluable, impactful resources when planted with pollinators in mind, bringing forage to new and very often nectar-depleted arenas, particularly those that are street-facing. Even the rural village where I live has a deceptively barren high street – it’s too narrow for street trees – and in places the pavements are entirely lacking greenery.
This was the motivation for installing my first window box last year, and the subsequent arrival of a bumblebee at the window was sheer joy: unexpected life inhabiting the roadside.
Which planter?
Window boxes come in almost every material – plastic, wood, metal, terracotta. Tastes will vary, but it’s best to choose something that will last, withstand frosts and provide at least 25cm of soil depth. Plastic can tick these boxes, and tends to be readily available from second-hand sources, while “fibrestone” planters retain the earthenware feel of stone or terracotta yet weigh a good deal less, which can be handy. Most important is to secure the box firmly in place, with brackets, hooks or a retaining bar or cage along the window ledge.
Prep and planting
A common mistake with window boxes is to opt for drought-tolerant species and then neglect the requisite drainage. Though a container might be shallow, if it has no drainage holes and no layer of grit at the bottom, plants can end up sitting in soggy soil, which is fatal for dry-climate species. Add an inch of gravel or horticultural grit to the planter bottom before filling the remainder with a peat-free compost, leaving room at the top for another layer of grit, which will act as a water-retaining, weed-suppressing mulch. Raising a planter on rubber or terracotta “feet” will also increase drainage.
Unusual plants to try in your window planter
For anyone looking to bring environment-minded dynamism to their sunward sills, what follows is a list of particularly robust and ever-giving plants suited to such conditions. They are divided into evergreens for year-round structural form and statement flowers for a long blooming season. Mixing the two can provide interest throughout the seasons. An 80-100cm planter of adequate depth will happily accommodate five or six plants of a one-litre pot size.
As the plants develop, snip foliage that is crowding adjacent plants, and cut back finished herbaceous flowers to encourage new blooms. During the growing season, feeding at intervals with an organic seaweed feed, diluted in a watering can, will restore nutrients to the limited soil. Increase watering in hot, dry weather.
Trailing rosemary (Rosmarinus officinalis ‘Prostratus’)
Blooms April-June
Rosemary remains one of the very best structural plants for small containers. Durable, fragrant and attractively floriferous in spring, the cultivar ‘Prostratus’ has the beneficial trait of trailing foliage. burncoose.co.uk
Myrtle spurge (Euphorbia myrsinites)
Blooms April-June
Evergreen euphorbias make fantastic container plants, given their drought tolerance and insect-luring flowers. The acid-yellow colours of compact E. myrsinites will enliven a perennial scheme. bethchatto.co.uk
Hedge germander (Teucrium x lucidrys)
Blooms May-July
This hybrid teucrium is surprisingly tough and woody for its height, with aromatic foliage and nectar-rich, pinky-mauve late summer flowers. ballyrobertgardens.com
Santolina ‘Edward Bowles’
Blooms June-July
A cotton lavender cultivar with pale pincushion blooms in midsummer, ‘Edward Bowles’ brings fine, glaucous year-round foliage. hardysplants.co.uk
Sicilian chamomile (Anthemis punctata cupaniana)
Blooms May-July
Chamomiles are hard-wearing herbs with universally adored daisy-like flowers: cupaniana brings silvery foliage and a compact habit ideal for the window box. hardysplants.co.uk
Calamint (Calamintha nepeta ‘Alba’)
Blooms July-September
A mint-fresh aromatic herb boasting an astonishing abundance of long-lasting nepeta-like summer flowers. jekkas.com
Cupid’s dart (Catananche caerulea)
Blooms July-August
This is an excellent cornflower-type perennial bearing narrow leaves and lavender-blue daisies on graceful, airy stems. shireplants.co.uk
Festuca mairei
Blooms August
This robust, low-growing tussocky grass provides excellent shelter for overwintering insects and turns golden in autumn. Trim back in mid-spring for fresh growth. barrettsbridge.co.uk
Keeled garlic (Allium carinatum ssp pulchellum)
Blooms July-August
Unlike many alliums, the narrow leaves of keeled garlic make it a fantastic container plant, with pink flowers clustered on sturdy stems. baileybordersplants.co.uk
Salvia nemorosa ‘Caradonna’
Blooms June-October
As appealing to pollinators as it is to people, the Caradonna is a great salvia, offering long-lasting blooms in vivid violet colours. crocus.co.uk
Hylotelephium telephium ‘Purple Emperor’
Blooms August-September
Purple leaves can add visual contrast to a scheme and the seductively maroon ‘Purple Emperor’ is great for attracting butterflies and moths. Hylotelephium ‘Vera Jameson’ offers a low-growing alternative for tighter conditions. claireaustin-hardyplants.co.uk
Artemisia stelleriana
Blooms June-July
This velvet-leafed member of the wormwood clan has proved a winner in my own window box, where I use it for underplanting the taller perennials with draping silvery foliage. macplants.co.uk
Spring bulbs
Bloom February-April
Planted in autumn, spring bulbs help lengthen the flowering window of a perennial scheme. Iris reticulata offers bold early colour, while the wild-looking Tulipa sylvestris and T. turkestanica (pictured) are among the tulip varieties that are most appealing to pollinators. farmergracy.co.uk
Coreopsis verticillata ‘Moonbeam’
Blooms June-September
Words cannot express how much I love this long-flowering, endlessly elegant perennial. Beloved of bees, it has light, finely cut foliage that doesn’t smother other plants. bethchatto.co.uk
Origanum vulgare ‘Thumble’s Variety’
Blooms June-August
Talking of insects, oregano is an exceptional source of nectar for a range of butterflies. The yellow-green leaves of ‘Thumble’s Variety’ also break up a predominantly green palette. bethchatto.co.uk
