7 Fall Gardening Mistakes That Will Ruin Your Perennials—and What to Do Instead

Autumn is the perfect time to get spring bulbs in the ground and prepare your vegetable garden for winter. However, with so much to do, it’s easy to make a mistake or two that could harm your perennials. These errors could lead to disastrous outcomes, including damaged roots and weakened plant health.

Here, we share advice from gardening experts about which seasonal mistakes to avoid this fall—and what you should be doing instead.

Cutting Back Too Early

Pruning too early can cause problems. “Cutting foliage before it naturally dies back prevents plants from storing enough energy in their roots, leaving them weaker when spring arrives," says Wendy Overbeck Dunham, director of horticulture at Frederik Meijer Gardens and Sculpture Park.

“Pruning before a plant is fully dormant can stimulate tender new growth that cold weather will damage,” adds Corey Ashford, gardening expert and partner at EarthSpoke Farm. Perennial roses, like Knock Out roses, are a classic example. They should only be cut back once dormancy has set in, he says—which in most climates makes it a winter task, not a fall one.

Instead of pruning too early, wait until the perennial foliage naturally yellows and dies back before cutting. “This allows the plant to finish sending energy to its roots and sets it up for a stronger start next season,” says Dunham.

Removing Fallen Leaves

Fallen leaves, stems, twigs, and branches are autumn and winter abodes for beneficial insects like pollinators. “A total clean-up removes the natural mulch and overwintering habitat that many beneficial insects depend on,” says Dunham.

Instead, tuck some leaves into garden beds as natural mulch, and keep hollow stems for insects to shelter in. This protects plants and supports biodiversity.

Transplanting Too Early

Another common mistake is transplanting perennials just before or during bloom. “Moving plants while they’re preparing to flower or actively blooming puts them under stress,” says Dunham. This is because the plant’s energy is directed toward producing flowers, rather than establishing roots.

Instead, she recommends transplanting spring-flowering plants after they bloom in mid-late summer, and moving fall bloomers in the spring.

Forgetting to Mark Plants

Once foliage dies back, it’s surprisingly easy to forget what’s planted where, says Ashford. Marking plant locations can help keep perennials from becoming overcrowded, which can cause them to lose their vigor and become more susceptible to disease.

“Perennials need space to spread their roots, so cramming them together in the fall can cause them to compete for nutrients, oxygen, and water,” says Rebecca Sears, a gardening expert at Ferry-Morse.

Instead, place placards to remind you of where your plants are in the garden. That way, if you add any new plants in early spring, you'll know where the other returning perennials are located. You'll also be able to ensure proper spacing between perennials.

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Not Watering Enough

Remember to keep watering your perennials, even in fall. “Cooler temperatures don’t mean that your perennials no longer need proper hydration,” says Sears. Remember, perennials are still storing energy for winter until the ground freezes, and therefore need to be consistently watered until the first frost.

Consider using a drip irrigation system. This is an efficient way to ensure your perennials are being deeply watered every week until the ground is frozen.

Not Considering Winter Interest

Removing every dormant perennial plant stem and seed head strips the garden of its structure and beauty. They also gather snow and ice, creating a winter wonderland effect in your garden that would be missed if you trimmed back all dead or dormant plant matter.

Leave ornamental grasses, seed heads, and sculptural stems standing. “They catch snow and frost, adding texture and light to the landscape,” says Dunham. “A snow-dusted grass plume glowing in the winter sun is a beautiful thing to see.”

Dividing Too Late

There are some perennials that you should always divide to keep them flowering year after year. However, dividing them too close to the frost doesn’t give them enough time to establish roots.

With dahlias, for example, large clumps of tubers can encourage rot. “We recommend dividing dahlias every three years or so, which can be a fall or early-spring task," says Ashford.

Divide or transplant 6 to 8 weeks before the ground freezes so that the roots can take hold before the frost.