Yarrow is a very hardy, native perennial that grows in a wide range of hardiness zones. In the colder zones, the plant behaves like an herbaceous perennial, meaning that it dies back to the ground completely during dormancy. In the warmer zones, Yarrow acts more like a semi-evergreen perennial.
During winter dormancy, the foliage and stems do not fully die back and remain all winter and then die back as the new growth emerges in the spring. The main enemy of Yarrow in the winter is bad drainage. If the soil is waterlogged during cold weather, the root ball will be starved of oxygen and rot.
Protecting Yarrow in Winter
Yarrow doesn't need much extra protection from the cold and snow of winter. Mulching around the plant will insulate the root zone and help drainage a bit. Since most of the plant will be gone in the winter, the only concern will be making sure that Yarrow doesn't accidentally get dug out or trampled in the spring as the new growth starts. Leaving the previous season's growth on the plant through the winter will help to insulate the crown a bit and indicate where it is in the garden. Marking with a stake or garden art is also an option if you clean Yarrow up in the fall. Completely covering the plant is unnecessary.
Cutting Back Yarrow for Winter
Yarrow is an herbaceous perennial in most of the hardiness zones it grows. The whole plant dies back as it goes dormant in the fall. Fall or spring pruning is entirely the gardener’s choice. Leaving the seed heads is appreciated by the birds over the winter. In fact, much of the old foliage and stems of Yarrow will help to insulate the plant crown and will mostly decompose by the next growing season. In the spring, a quick clean up of any plant material remaining is all that Yarrow needs to help regrow.
Yarrow Winter Care in Pots
Yarrow growing in containers needs a bit more attention to its position and watering during the winter months. Plants in containers do not have the added benefit of insulation that a garden bed provides. Extremes of heat and cold are felt more harshly by the plant's roots. Using containers that have more insulating qualities such as plastic or resin will help protect the plant during extreme temperatures. Since Yarrow is very hardy, wrapping the pot in burlap or horticultural fabric is not usually necessary. Make sure that yarrow experiences excellent drainage all winter long and the pot does not become waterlogged.
Watering Yarrow in Winter
Yarrow will rarely need extra watering during the winter months. Overwatering because of non-draining soil is the most concerning issue. Clay soils can hold onto water longer in the winter when they are cold. Also, run off from driveways, houses, garages, etc can be greater in heavy winter rains and may cause seasonal ponding in low spots of a garden. If this is happening, Yarrow can be dug out and temporarily potted for the winter.
Place the pots in an unheated greenhouse or sheltered area of the garden that is out of any prevailing storm paths or wind. Once the drainage issue is fixed, Yarrow can be planted back out in the garden. Treat these plants like they are newly planted for at least the rest of the growing season.
Growing Yarrow Indoors
Yarrow needs a period of dormancy in the winter to remain a vigorous and strong bloomer. Bringing these plants indoors will not keep them from going dormant. In fact the warm, low-light, dry conditions of the indoors will reduce Yarrow's vigor.
Steps to Care For Yarrow in Winter
Step 1 - Make sure Yarrow has excellent drainage all through the winter.
Step 2 - Cleanup the previous year’s growth in fall or early spring.
Step 3 - Make sure to mark where Yarrow is in the ground while it is dormant.