How to Overwinter Rosemary, Bay, and Tender Herbs

Know Which Herbs Need Help

Well-established rosemary survives winter lows down to about 18°F and bay laurel is generally hardy down to about 23°F, according to the Royal Horticultural Society. Where winters stay above those marks, protect the plants outdoors with mulch, fleece and wrapped pots. Where winters go lower, bring them indoors before the first frost and keep them cool, very bright and on the dry side until spring.

In USDA zone terms, University of Illinois Extension rates rosemary hardy to zone 7 and warns that single digit temperatures are often fatal. NC State Extension lists bay laurel for zones 8b to 10b and advises bringing it indoors for winter anywhere colder than 8b. Bay is the more tender of the two.

Planting position changes the picture. The Royal Horticultural Society notes that a bay planted in the ground is hardier than one in a container, and that bay may survive below 23°F in a sheltered spot. Roots in a pot are more exposed than roots in the ground, so a potted herb needs help sooner than the same plant in a bed.

Illinois names rosemary, sage and bay among the plants gardeners commonly carry through winter indoors. Many other kitchen herbs come back by themselves, and our guide to perennial and annual herbs sorts out which is which.

Decide: Protect in Place or Bring Indoors

Compare your usual winter low with the limits above. A zone 7 garden sits inside rosemary’s rated range. A zone 6 garden is borderline, and Illinois points to two rosemary varieties noted for zone 6 hardiness, ‘Arp’ and ‘Hills Hardy’. Colder than that, plan to move the plant.

For rosemary staying outdoors:

• Add a layer of heavy mulch at the first frost, as Illinois advises.
• During severe cold spells, cover the plant with burlap, an old bedsheet or frost fleece. The Royal Horticultural Society recommends this to prevent damage to the shoots from hard frost and cold wind.
• Group pots together, wrap them in blankets or bubble wrap, and move them against a building wall or into a greenhouse.

Wet is as dangerous as cold. The Royal Horticultural Society warns that cold, wet potting mix can cause rosemary roots to rot and die, and suggests moving containers out of heavy rain even in a mild winter. If a potted rosemary has struggled before, check the drainage fixes for rosemary before winter sets in.

For bay staying outdoors, the Royal Horticultural Society’s steps are similar. Cover the plant with fleece when the temperature drops below 23°F, wrap the pot in burlap or bubble wrap so the roots do not freeze, and raise the container on pot feet so it drains. Its alternative is to move a potted bay into a garage or cool room kept at no more than 50°F.

Moving Plants Indoors

Illinois sets the deadline: bring tender plants in before the threat of the first frost. Waiting for the plant to show cold damage is too late.

Start with an inspection. Look over each plant for signs of pests and disease, and rinse the leaves with water to wash off small insects. Illinois advises bringing only healthy plants inside, since anything on the leaves will spend the winter in the house with the rest of your plants.

Illinois suggests cutting tender perennials such as geraniums and coleus back by half before the move. Go more lightly with rosemary. The Royal Horticultural Society’s pruning advice for rosemary is to trim after the flowers fade and to avoid cutting into old wood.

A rosemary or bay growing in the ground has to be lifted and potted first. Illinois notes that if the plant is small enough, the entire plant can be dug up and planted in a container of fresh potting soil, and the same first-frost deadline applies.

Where to Keep Them Indoors

The target is a place that is cool and bright at the same time. Illinois recommends around 50 to 60°F with very bright sunlight for rosemary, and notes that most homes are too warm and too dry for it. University of New Hampshire Extension suggests a cooler range still, 45 to 55°F, and reports that it improves survival. An unheated sunroom, an enclosed porch that stays above freezing, or a bright window in a spare room with the heat turned down comes closest.

New Hampshire places rosemary in front of a south-facing window. If you have no window that bright, Illinois advises supplemental lighting, and our guide to grow lights for herbs in winter covers the options.

For a potted bay, the Royal Horticultural Society’s suggestion is a garage or cool room at no more than 50°F during the coldest weeks.

Watering and Feeding Through Winter

Water by the state of the pot. New Hampshire’s rule for rosemary is to wait until the potting mix is very dry, then water well enough that it drains from the bottom into the saucer. For tender plants in general, Illinois gives a similar test: water when the top inch of soil is dry, until water flows from the drainage holes. New Hampshire adds that plants kept at cooler temperatures need watering less often.

Hold the fertilizer. Illinois states that overwintering plants do not need feeding because they are not actively growing. For bay, the Royal Horticultural Society’s feeding season runs from mid-spring to late summer, which leaves winter out.

Pests and the Move Back Outside

Check the plants every week or two while they are indoors. Spider mites can turn up on rosemary indoors, and one option New Hampshire gives is to spray the foliage with a heavy stream of water every day or so to knock them off. The fuller routine is in our guide to getting rid of spider mites on houseplants. On bay, NC State lists scales and psyllids as occasional pests, and the Royal Horticultural Society names bay sucker and scale insects. Look along the stems and on the undersides of the leaves.

In spring, the whole plant can go back outdoors. Bay that has picked up frost-damaged leaf tips over winter can be tidied with a light pruning in late spring, per the Royal Horticultural Society. The same source recommends repotting a container bay every two years in spring, so the move outside is a good moment to do it.