It's common to think that everything should be chopped down to the ground in the fall, but some perennials actually need their foliage to protect new shoots through the winter. Other varieties offer up important habitat for local wildlife and some perennials provide height and interest through the winter months.
However, there are cultivated plants which are more susceptible to problems if the old foliage and dying stems are left to rot. Diseases can overwinter in dead foliage, as can slugs and other pests. Old stems can also get battered about by fall and winter winds, which will damage the plant's crown and roots.
Some perennials, like hostas, peonies and daylilies, need to be pruned in fall to avoid winter damage. Plants like these should be pruned after the first few frosts in late fall or early winter. Other perennials like mums and coneflowers are better off being pruned in spring just before new growth comes in.
Some perennials benefit largely from regular pruning during the summer growing season, but the most important cleanups are in the fall and the spring. A host of perennials respond best to a tidy spring cleaning and are seemingly rejuvenated from the practice.
Start the winterizing process by mulching around landscape plants. Mulch helps insulate soil and prevent frost heave, a condition that occurs when soil repeatedly freezes and thaws—and pushes plants out of soil. When frost heave occurs, plant crowns and roots are exposed to freezing air and drying winds.
Cutting back perennials in the fall is not only a great way to keep flowerbeds looking neat and tidy through winter, but it also aids greatly in keeping plants vibrant and blooming the following year. Removing spent foliage and blooms helps a plant focus on recharging it's roots and resources.
In the crunch of fall chores and yard cleanup, you'll have to carve out some time to tend to your garden perennials, too. It's important to cut back foliage in the fall to protect flowering plants from disease and give them a clean start for regrowth as winter starts to turn into spring.
Many gardeners cut back their perennials much too soon. There are nuances specific to certain perennials that dictate whether it is better to cut them back in fall or spring, but the general rule I like to follow is to only cut back perennials that start looking bad in fall.
After a few years in the garden, these perennials may start to produce smaller blooms, develop a 'bald spot' at the center of their crown, or require staking to prevent their stems from falling over. All of these are signs that it is time to divide.
The good news is that hostas, also known as plantain lilies, are tough and forgiving plants. Even if you forget to prune them at a certain time or you neglect to prune them at all, they'll still survive just fine, even if they don't look their best.
Daylilies are best cut back in autumn, once the leaves have had a full growing season on the plant. While there are some evergreen types of daylilies, most are herbaceous, meaning that the leaves die back in the wintertime and sprout anew in the early spring.
Q: When is the best time to cut back in the fall? A: “When they start to look too ratty for you and before the fresh new growth begins,” says Sarah. For plants that are frost-sensitive, wait until after the plants have gone through several hard frosts to ensure they're dormant before cutting back.
Although each plant's needs may vary and some will be more winter-hardy than others, in general about a month before the last fall frost is sufficient in giving the plant enough time to establish itself and take root.
Spring-blooming perennials, especially in the bare root form, are best planted early in the fall. Planting in the fall while the soil is still warm will give the roots enough time establish properly. This allows the plants to emerge from well established roots, with a stronger start, the following spring.
The spent flowers quickly turn to a mushy bloom and then dry over undeveloped buds which can prevent them from opening. Removing the dead blooms keeps this from happening. Also, daylilies which have not been deadheaded will form seed pods.
Overwintering Techniques
The general consensus seems to be that the best way to overwinter containerized perennials is to take the entire pot and bury it in the ground. This way, the roots are protected like they would be if the plants were actually planted in the garden.
Fabric coverings will prevent the freezing air from coming into direct contact with the moisture on the plant while also capturing the heat that is radiating from the ground. Bed sheets or comforters work best for covering large plants and shrubs.
If the soil is dry and the cold front is not preceded by rainfall, water the landscape before the freeze. Watering 24 to 48 hours before the freeze will elevate the night temperatures by 2 degrees. Don't overdo it. A soggy soil is not healthy for plant roots and will create root disease problems down the line.