Chapter 10

Winter Dormancy

Hostas need winter. The trick is getting them through winter without losing crowns to voles or to the freeze-thaw cycle.

What dormancy is

Dormancy is not death. The visible plant — leaves, petioles, scapes — does die back completely each fall, but the underground crown is alive and metabolically active at a low level. During winter the crown rests, then breaks dormancy in spring once it has accumulated enough chill hours below 40 °F. Hostas need roughly 6 weeks of chill to wake up properly the next year. Ohio gives them three months of it; they're delighted.

The fall cleanup

After the first hard frost (usually late October to early November in central Ohio), the leaves go from green to yellow to mush in about a week. This is the cue to clean up.

1. Wait for the first hard freeze. Don't cut leaves down while they're still green — the plant is still pulling energy back into the crown.
2. Cut all foliage to 1 inch above the crown. A sharp pruner or hand shears does it. Bag the trimmings and put them in the trash, not the compost — slug eggs and possibly virus tissue overwinter in old hosta leaves. This is one of the few places I'd discard rather than compost.
3. Remove all debris from the bed: fallen tree leaves smothering the crown, dead annuals, the litter that always accumulates. A clean bed under winter mulch is what you want.
4. Mark the plants. Once the foliage is gone the bed looks empty and is easy to forget where things are. A bamboo stake next to each crown saves a lot of spring-time guessing — especially useful if you plan to plant bulbs over the hostas.

Winter mulch

The reason for winter mulch is not to keep crowns warm — it's to keep them cold. The freeze-thaw cycle of an Ohio February (40 °F by day, 18 °F at night) heaves shallow-rooted plants out of the soil. A thick winter mulch keeps the ground frozen and the plant in place until proper spring.

• Apply 3–4 inches of shredded leaves, straw, or pine bark after the ground has frozen the first time (usually mid-November).
• Keep mulch 2 inches off the crown. Mulch volcanoes against crowns are an invitation to rot and vole damage.
• Remove the bulk of winter mulch in late March as you see noses pushing through. Leave 1–2 inches as a permanent summer mulch.

Voles in winter

The biggest threat to a hosta bed in February in Ohio is not the cold — it's voles tunneling under the snow and eating roots from below. The whole bed can look fine in March, and then half the plants come up looking sickly because their roots are gone.

Prevention:

• Keep mulch pulled back from the immediate crown area through winter.
• Set out a few mouse-style snap traps under inverted boxes or pieces of bent hardware cloth in known vole runs along the bed edges. Bait with peanut butter.
• For high-value plants, plant the rootball inside a hardware cloth basket (see Chapter 7).

Container-grown hostas in winter

Hostas in pots are in trouble. Above-ground containers freeze and thaw far more violently than in-ground soil — the roots experience the air temperature, not insulated soil. To overwinter potted hostas in Ohio:

• Sink the pot to its rim in a garden bed for the winter, then dig out in spring. Best option.
• Cluster pots against a north or east wall, surround with bags of leaves or straw to insulate, and cover the cluster with a tarp. Works.
• Move to an unheated garage. The cold protection is more than enough; the issue is light loss isn't a problem since the plants are dormant, but you must remember to check soil moisture once a month — desiccation is the failure mode here.

Spring wake-up

In Ohio, the first noses (pointed, pinkish-purple, asparagus-like shoots) emerge from late March to mid-April depending on weather. A late frost after noses are up can blacken those first leaves; the plant will replace them, but the second flush is smaller. To protect prized plants during a forecasted late freeze, throw an old bedsheet (not plastic) over the noses overnight and remove in the morning.