In the ground: usually little to do
Established, hardy ornamental grasses planted in the ground generally need very little winter protection. In fact, the main thing most of them need is to be left alone. The standing foliage insulates the crown, traps snow, gives structure to the winter garden and shelters birds and insects.
A few points to keep in mind:
- Do not cut back for winter unless you have a reason such as fire risk. Cutting in late winter or early spring is the usual approach. See cutting back ornamental grasses for details.
- Stop feeding in fall. Late fertilizer can push soft growth that is damaged by cold, and some sources note it can reduce winter hardiness of warm-season grasses. More on this in whether to fertilize ornamental grasses.
- Check drainage. Wet, cold soil is harder on grasses than cold alone. Many grasses prefer soil that is not waterlogged in winter.
- Water if it has been dry. If fall has been dry and the ground is not yet frozen, a deep watering helps.
Mulch and newly planted grasses
Grasses planted this season have not yet built a strong root system. Missouri Extension suggests a light mulch applied after several hard freezes in the first winter for fall-planted grasses. A layer of shredded leaves or similar material is typical, though avoid piling it directly over the crown. Winter protection is generally not needed in later years.
If you planted late and are worried about the plants, our guide on planting ornamental grasses covers timing, and the fall checklist covers what else to do in autumn.
Tender grasses
Some popular grasses are not hardy in cold climates. Purple fountain grass (Pennisetum setaceum ‘Rubrum’) is a common example, hardy only in the warmer zones, and is usually grown as an annual elsewhere. Your options are to replace it each year, or to dig it up in fall, pot it, and keep it in a bright, cool indoor spot with occasional watering. Not every plant comes through the winter this way, so treat it as a bonus rather than a certainty.
True pampas grass (Cortaderia selloana) is also described as not reliably hardy in colder regions. Gardeners in cold areas sometimes choose hardier lookalikes such as plume grass (Erianthus ravennae, sometimes sold as hardy pampas grass), though check hardiness for your zone before buying. Cold-hardy grasses for zones 3 and 4 lists reliable options for the coldest gardens.
Grasses in pots: why they are at more risk
Plants in containers have less insulation than plants in the ground, because the roots are exposed to cold air on all sides. A common rule of thumb is that a potted plant is less hardy by roughly one to two zones than the same plant in the ground. Pots can also freeze solid, and clay or ceramic containers may crack. Wet soil in a pot that cannot drain is another hazard. For more on growing in containers, see do ornamental grasses do well in pots.
Options for potted grasses
- Leave outdoors in a sheltered spot. In milder climates, large pots against a wall can come through winter. Group pots together for mutual protection, and consider wrapping them. Move them out of heavy rain if possible.
- Sink the pot into the ground. Burying the whole pot in a garden bed insulates the roots. Mulch over the top.
- Move to an unheated garage, shed or cold frame. Hoffmann Nursery notes that many grasses overwinter well in a cold frame, which protects roots and keeps rain from over-soaking them. A cold, frost-free but unheated space works for many hardy grasses.
- Plant them out. If you will not use the pots again, you can plant the grass in the garden in fall (early enough to root) or spring.
Watering in winter
Dormant grasses need little water, and overwatering is a bigger danger than drought. Keep containers on the dry side, but do not let the root ball dry out completely. A light watering roughly once a month during dry spells is a common suggestion for stored pots. Never let a pot sit in standing water.
Spring wake-up
When growth resumes, move pots back out gradually, cut back old foliage, and refresh the top layer of potting mix. Container grasses that have outgrown their pots can be divided; see dividing and transplanting ornamental grasses.
Frequently asked questions
What fertilizer is good for pampas grass?
Pampas grass and its look-alikes generally need only a light spring feeding at most, using a balanced fertilizer or compost. Avoid late-season feeding. See our fertilizing guide.
What are some popular perennial tall grasses?
Miscanthus (maiden grass and relatives), feather reed grass, switchgrass, plume grass and Indian grass are all widely grown tall perennial grasses. Hardiness varies, so check your zone. See tall ornamental grasses for privacy screens for sizes and uses.