What to do with alliums after they finish flowering

Are the impressive pom-pom blooms of your ornamental allium plants past their best? Before you reach for the secateurs at the first sight of frazzled petals, it’s useful to know what to do with alliums after they finish flowering.

When daffodils finish flowering, for example, it’s better to leave them be for a while so that the bulb below ground can get enough nutrients to survive the winter and return triumphant next year. But not all bulbs are the same.

Alliums are a hero plant for beginner and expert gardeners alike. They’re one of the best low-maintenance garden flowers for your patch – rewarding minimal effort with generous plumage. In fact, alliums are so easy-going that it’s really up to you if you want to cut the flowers back or not.

We spoke to gardening experts to explain what to do with alliums after they finish flowering, so you can make the best decision based on your garden’s needs.

You can cut alliums after they finish flowering

Alliums aren’t like most bulbs, according to Monty Don

Some people can’t bear the sight of crispy, withering leaves and petals. Those keen to clear any raised beds of spent flowers, including alliums, will be pleased to hear that they can wield their scissors in confidence.

“Unlike most bulbs, the foliage of alliums can be cut back immediately after flowering,” writes Monty Don. “In a border this will create space for planting tender annuals such as cosmos, zinnias, tithonia or sunflowers.”

Small garden owners may want to switch up flower displays as much as possible – in which case you can cut alliums back. Though it’s best to give the bulb some time to absorb nutrients through its faltering leaves.

Wait for foliage to turn yellow

“If you’re keen to tidy alliums up more immediately, wait for the foliage to shrivel and turn yellow, then snip the stem at the base with clean, sharp secateurs,” says Sarah Veniard, garden designer and founder of Discovering Gardens.

“It’s important to be patient and wait for the foliage to die back as, even after flowering, the leaves are still photosynthesising and sending valuable energy into the bulb. This will allow the bulb to over-winter successfully and provide you with a magnificent display again the following year.”

Leave alliums alone when they finish flowering

“Just let them do their thing”

Even though alliums are tremendously hardy perennials, not touching them after flowering is the best way to ensure they return in the best health.

“Just let spent alliums do their thing, Guy Barter, chief horticulturist at the Royal Horticultural Society, tells us. “The leaves die back to nourish the bulb and the seedheads dry out gradually to look very architectural, particularly when frosted.”

Veniard agrees that alliums can be valuable in the bleaker winter months. “If left in the garden, the spent flower heads will continue to provide their gorgeous sculptural form to your borders into winter, providing interest when your other plants may be going dormant,” she says.

“Don’t water spent plants and leave potted ones to get a good bake but not become totally desiccated,” Barter adds. He notes that autumn rain and winds will cause some alliums to collapse. “Consign them to the compost bin," is his advice.

Other uses for alliums after they finish flowering

Feed the birds and fill your vases

Calling all flower arrangers: dried alliums are a wonderful addition to a vase. “You can cut the seedheads and dry them inside,” says Veniard. “They make a fantastic decoration in a vase; particularly beautiful when accompanied by the soft, wispy stems of dried grasses.”

Barter agrees that the dried seedheads look good as indoor arrangements. “You can cut the flowers in bloom and dry them indoors,” he adds. “Some colour is often retained, but it seems a waste."

Leaving the seedheads to dry on the flower in the garden has another use. Birds will enjoy snacking on the dried seeds. You can also collect the seeds yourself to grow more alliums from scratch yourself.

“But given the low price of bulbs and the time and space needed to raise plants to flowering size [often a couple of years], few gardeners bother,” explains Barter.