Let the garden go to seed in style

There comes a time in every gardener’s life when you learn to embrace the unexpected. A shining example is the ability of certain plants to gently self-seed into the most unlikely and yet most appropriate of locations. Tiny, dark crevices in walls, narrow gaps between paving stones, niches in crumbling stone structures, neglected shady corners, even rotting tree stumps . . . in other words, the kinds of challenging planting spots within the matrix of a garden that can confound the most skilful of gardeners, yet which prove no obstacle to tiny seeds determined to germinate and grow.

It’s not, I should add, that I’m advocating complete horticultural anarchy. But the very best kinds of self-seeders – the kinds that gardeners happily welcome rather than mournfully regret the day they were ever allowed entry – will populate a garden in a way that’s artful yet discreet so that they somehow always look right at home.

These are the kinds of plants that can magically soften the hard lines of a patio or a flight of steps, add a pretty frill of foliage and flowers to the edges of a border. When it comes to pebble paths (one of their all-time favourite spots) they will gently colonise these in a way they rarely would with a conventional border.

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Borage, with small, star-shaped, periwinkle-blue edible flowers

A classic example is the dainty Mexican fleabane (Erigeron karvinskianus), a low-growing, long flowering, clump-forming perennial whose pink-and-white, pollinator-friendly daisy-like blooms appear from May until October. Happy in sun or light shade and tolerant of coastal conditions, it will sprinkle itself about the garden in a way that never feels obtrusive. A sharply-drained soil is all that this garden stalwart asks for, which is why it favours pebbled areas, paving cracks and gaps in old stone walls.

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Foxgloves (Digitalis) have a similarly uncanny ability to self-seed into all kinds of seemingly inhospitable spots in the garden, as do Welsh poppies (Papaver cambrica), lady's mantle (Alchemilla mollis), spring-flowering columbines (Aquilegia), valerian (Centranthus), some perennial geraniums (for example Geranium "Bill Wallis"), the tall, lilac-flowered Verbena bonariensis, the ornamental grass known as Stipa tenuissima and the graceful perennial toadflax (Linaria purpurea).

Generous self-seeders

Other examples of generous self-seeders include the annual herb known as borage, whose small, star-shaped, periwinkle-blue edible flowers are a very pretty addition to a salad or summer cocktail. Grow it just once in your vegetable patch and you should have it forever, with young self-sown seedlings typically appearing in profusion in late spring.

The same goes for the pot marigold (Calendula), a well-known annual and a prolific self-seeder whose jolly orange, daisy-shaped flowers are a staple of many summer kitchen gardens. An added boon is that some self-sown marigold seedlings inevitably turn out to be quite unlike their parent plant in terms of flower colour, producing blooms in charming shades of rusty cream, buff and pale yellow as well as gold. Grow them alongside a few nasturtiums (yet another prolifically self-seeding annual with edible flowers in fiery shades of orange, crimson and yellow) and your allotment or kitchen garden will never want for colourful, edible summer blooms.

Other ornamental self-seeders appear in the garden as if by magic, uninvited yet nonetheless welcome for it. A classic example is the annual opium poppy (Papaver somniferum) whose tiny seeds are often carried into a garden as secret stowaways, invisibly hitching a lift on the compost of a freshly purchased plant or perhaps dropped by a passing bird or carried on the boot of a visiting gardener friend. Fast-growing, this poppy's short-lived yet flamboyantly beautiful flowers open overnight like tropical butterflies blown off course by a summer hurricane. Scarlet, plum, flamingo pink, and in both single and double forms, these are followed by long-lasting seedheads so ornamental that you can't help wishing you could draw, sculpt or cast them in bronze.

Late summer is, of course, the time when most of the plants I’ve mentioned start to set seed, making it a great time to introduce a few of them to your garden.

The trick to helping them to establish lies in firstly, allowing the parent plant to set seed (don’t deadhead flowers as they fade, instead allow the seed to ripen and spill); secondly, positioning that same parent plant (container-grown specimens are easiest to position) in a spot where at least some of its ripe seed is likely to end up spilling down into those aforementioned cracks, crevices, pebble paths etc; and thirdly, avoiding the use of weedkillers, ruthless handweeding or overly vigorous hoeing so that once they’ve germinated (which might not be until next spring), the tiny seedlings can grow on undisturbed.

In other words, adapt a slightly laissez-faire, nature-friendly attitude to your garden that will allow plant colonies to naturally establish over time. Once those young colonies have established, then it’s a simple matter of weeding out any unwanted plants or transplanting them as young seedlings into other parts of the garden. Or you could always pot a few up and give them to gardening friends as gifts.

Just tell them to expect the unexpected.

This Week in the Garden

Many kinds of vegetable plants including tomatoes, French beans, runner beans, courgettes and cucumbers are now at their most productive. So regular picking is really important in order to encourage as long a harvesting period as possible. Manage gluts by turning all that delicious homegrown produce into sauces or soups that can be bunged into the freezer. Most vegetables (including tomatoes) can also be frozen whole; see bbcgoodfood.com for tips on blanching and open-freezing freshly-harvested produce from the garden.

Order seeds of hardy annuals to sow later this month/early September. These autumn-sown plants will be much sturdier, more prolific and earlier to flower next summer than their spring-sown counterparts.

Suitable kinds include varieties of cornflower (Centaurea cyanus), the purple-flowering ornamental carrot (Daucus carota), love-in-a-mist (Nigella), Orlaya and Scabious (Scabiosa atropurpurea). Seed is available from most good garden centres or to order from online specialist suppliers including Mayo-based Seedaholc (seedaholic.com) and UK-based Sarah Raven (sarahraven.com)

Once the scented, purple flower spikes of lavender (Lavandula) have faded, shear away the dead flowerheads along with roughly an inch of this year's growth, making sure that some young, green growth remains (the plant doesn't re-grow easily from old wood) to encourage a bushy vigorous plant that will flower well again next year. Badly neglected, woody specimens are best replaced with new plants.

Dates For Your Diary

Tomorrow (Sunday, August 6th, 10am-5pm), Farmleigh Plant Fair, Farmleigh House, Phoenix Park, Dublin. farmleigh.ie