Herbs hardy enough to survive winter

Their leaves are rough or leathery, in shades of gray or blue-green. They thrive among sand and rocks and gravel. Though often woody, they’re kept low and scrubby by the nibbling of goats, and by occasional fires, fueled by the volatile oils from their aromatic leaves.

These are the classic garden herbs, celebrated in kitchens and folk ballads, from “Scarborough Fair” to Colonial Williamsburg. Rosemary, sage, winter savory, marjoram and thyme are so commonly grown, it is hard to remember that they were born to hate the rich soil of our gardens, and sometimes our climate as well.

Most of our popular herbs come from the Mediterranean region, a biome characterized by moist, mild winters and dry, hot summers. Usually, when we consider plants for our gardens, we go by the USDA Winter Hardiness Zone Map, which is based on minimum winter temperature. For Mediterranean herbs you’d be better off following the prophecies of Nostradamus.

With some, to be sure, winter cold is a factor. Annuals like basil, so resplendent on the Ligurian coast of Italy, must be replanted each year in an area with any frost. Lemon verbena, a deciduous shrub, is a zone 8 plant that will survive the winter only in a very sheltered spot, with a good mulch.

Certain other Mediterranean herbs seem indestructible. Oregano (Origanum vulgare) is a bushy plant that overwinters reliably. Sage springs forth anew each spring, though you might have to give it a stern pruning to improve the shape of the plant. Mint and chives are never a problem.

It’s all those in-between ones that are hard to predict. Common thyme, the cooking kind (Thymus vulgaris) is considered hardy to zone 5, but just barely squeaks by in my herb garden, even though it is shielded there from cold winter winds. Tarragon rises in splendor there every winter, but is winter-killed in our more exposed farm beds.

English lavender will weather severe lows in one garden, only to vanish utterly down the road. Winter savory, rosemary, lemon balm, salad burnet and bay might also live for one gardener, die for another.

It’s mostly about drainage. The roots of Mediterranean plants are adapted to drought, not to wetness. Even when there is rainy winter weather in the hills of Provence, Greece or their other haunts, it drains down the slopes, and percolates through soils aerated by stones and grit. Even the relative poverty of the soil seems to favor success.

There is quite a bit a gardener can do to make these plants feel at home. I’ve had good luck planting them on a sunny, south-facing slope. My formal herb garden is divided into sections by stone and gravel walkways. The herbs planted next to the gravelly paths are superbly healthy because excess water drains away from their roots. If your site is irremediably sump-like, raised beds might save the day.

Anything you can do to keep the soil well-aerated in winter is helpful. It should be loose and fluffy so that water cannot accumulate and fill the air spaces plant roots need to breathe. Dig in plenty of organic matter, especially compost.

Builder’s sand can be added to a heavy soil as well, but depending on how much clay you’ve started with, you might have to add as much as 50 percent sand to improve the texture, and you will still need to add organic matter as well.

Some gardeners add chicken grit (available from feed stores), which is usually composed of ground-up oyster shells or granite meal. It makes a good surface mulch for herbs, too, since it helps keep the crowns dry. Crowns are often as prone to winter rot as the roots are, especially with winter savory and thyme.

When you plant perennial herbs, leave plenty of space between them, to let air circulate. However, since cold winds can do them harm, and it’s wise to choose a location sheltered by a windbreak.

Don’t feed herbs or prune them heavily after late summer. Both will trigger fresh new growth that is vulnerable to the cold. Leaving top growth to catch blowing leaves also protects them from cold and wind.

Mulches help because they moderate the fluctuations of soil temperature that are hard on plants in wintertime. But don’t mulch with anything like flat autumn leaves that can mat down and make the ground even soggier. Instead, wait until early winter when the ground has frozen and apply evergreen branches. The time when everybody is discarding their Christmas trees is just about right. Remove them by April, in time for new growth to begin. Remove dead leaves and debris, also. Often the worst damage occurs in the dreariest part of mud season, when most of these plants are wishing they were on Corfu or in Portfino. And who could blame them?

Barbara Damrosch

Barbara Damrosch

Barbara Damrosch’s latest book is “The Four Season Gardener’s Cookbook.”
Barbara Damrosch

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