How should I prepare my perennial beds for winter?

FAQ
Question: 

How should I prepare my perennial beds for winter?

Answer: 

Perennial plants can be cut back in fall after the foliage has been destroyed by a hard freeze.  Compost the plant debris. While this work can be done, it is not necessary to clear cut the perennial garden after the first freeze of the season. Leaving the leaves, stems, dried flowers,and seed heads of many perennials provides more interest through the winter months. Leaving the plant materials also provides an extra layer of protection for the crown and root system of the perennial. Plus, the dead stems and leaves collect fallen leaves adding even more protection. Leaving the plant material in place and removing it in early spring instead of fall also helps provide food and protection to native pollinators, beneficial insects, and wildlife, like birds. While it is largely beneficial to leave foliage in place through winter, removal of plant material in the fall after it has naturally died back should be done for those perennials that had disease or insect pest issues during the summer. Additionally, those perennials that tend to be weedy or spread aggressively by seed benefit from late season deadheading and clean up to prevent them from being too weedy.

Leaving plant debris in place over the winter months can help those shallow rooted perennials that may frost heave. Frost heaving happens when the freeze-thaw cycle of the upper layer of soil works the crown and root system of the perennial plant out of the ground. If more protection is needed to prevent frostheaving, apply about four inches of mulch over the crown of the plant after the ground freezes, typically by late November in much of Iowa. Do not place the mulch on too early as it can slow plants from going dormant and make them more susceptible to damage from cold temperatures. Remove the excess mulch “blanket” in early spring as soon as the top layer thaws, typically around mid-March in much of Iowa.

Tender perennials and perennials planted in late summer/early fall should also be mulched to prevent injury.  These plants can also be protected with cages placed around the plants and filled with straw,  pine needles, or chopped cornstalks. As with extra mulch, place the protective layer late in the fall season and remove it in early spring. A 6- to 8-inch-layer should be adequate for most perennials. Do not use Styrofoam cones or domes as they can cause premature warming in the early spring bringing plants out of dormancy early and making them more susceptible to cold damage.Additionally, most plants will not fit under these cones without extensive pruning and it is better to prune in spring rather than fall.

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