8 Plants You Shouldn’t Deadhead Until After Summer Ends

Coneflowers

All coneflowers are best left alone until after summer has officially passed. In addition to providing some texture and structure in your garden in the fall, their seed heads are an essential source of food for native sparrows, finches and the American Goldfinch, notes Andrew Bunting, vice president of horticulture at the Pennsylvania Horticultural Society. 

“After feeding occurs and the seeds are removed by the birds, the seed stalks can be cut to the ground,” Bunting says. “You can also leave up the stems for the winter. Insects will use the chambers of the stems for overwintering.”

Sunflowers

Sunflowers also produce seeds that are high in protein and provide birds with food far into the winter. “If you cut them back too quickly, your garden will lose its place in the ecology,” Porwol explains. “They can be deadheaded once the seed heads are picked clean by wildlife, which, depending on your local climate, is usually by January.”

Poppies

Once they’ve bloomed, poppy blooms last anywhere from a few days to about two weeks. You might be tempted to prune them back after their heads have wilted, but it’s better to wait.

“Poppies are important to leave with their blooms intact as they wilt, so they re-seed in the fall and spring forth in the spring and summer for you,” explains Cindy Ollig, gardening expert and owner of The Perfect Petal.

Hardy Begonias

This hardy perennial actually blooms in early fall, so a snip in summer is premature. “The flowers are followed by attractive seed heads, and leaving them will result in plants dropping seeds and resulting in new seedlings serendipitously appearing the next spring,” Bunting explains. “The seed heads can ultimately be removed [in late fall] by pruning the stem that supports the seeds to the ground.”

Hydrangeas

Hydrangeas are another plant you should avoid deadheading. “Most hydrangeas have decorative seed heads, and I would actually encourage leaving them on versus removing them,” Bunting says.

Also, many hydrangeas set their flower buds for next year in late summer or early fall. Heavy pruning could accidentally remove next year’s flowers. 

Ornamental Grasses

Ornamental grasses—like miscanthus and pennisetum—offer a plush, verdant look to your yard in the summer months, but don’t write off their beauty once that green hue fades. “Their seed heads catch the low autumn light beautifully and also provide frost interest,” Porwol says. (In other words, they look gorgeous even in the winter). 

He adds, “According to a recent report by the Royal Horticultural Society, leaving seed heads in place enhances biodiversity because dead flowers provide cover for insects that hibernate.” He says to leave ornamental grasses alone until early spring, just before new growth starts.

Lavender

This part-herb, part ornamental grass smells heavenly from late spring to early summer, but don’t clip it back just because the scent has faded. “Lavender provides late-season bees with a second rush of perfume and nectar if it is not pruned too soon,” Porwol says. “You should deadhead it right after its first bloom in summer, which is usually July, to encourage a second flush. But come late summer, let the second bloom fade naturally and trim it back only in spring, once frost risks pass.”

Sedum

Sedum is another plant you shouldn’t deadhead before fall due to its beauty and ability to provide wildlife with food and shelter, Porwol says. Sedum blooms late in the growing season, often from August to October, offering one of the last reliable nectar sources for flying pollinators like bees and butterflies. 

Even after flowering, sedum seed heads can attract birds, and the dense growth and dried flower stalks can offer shelter for overwintering. “For sedum, especially varieties like ‘Autumn Joy’, cut back once the heads start collapsing under snow, which is typically late February,” Porwol says.