Wintering Herbs Indoors

Rosemary’s journey from garden to pot: How to choose and take care of the “in” crowd.

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September. The harvest of herbs is winding down, and the frenzy of trying to keep ahead of the weeds has abated. There’s an overwhelming tendency to give up, relax, and forget about gardening until the new seed and nursery catalogs start arriving in January. Herb gardeners who live where winters are frost-free may be able to get away with this, and those in more rugged climates whose only herbs are annuals such as dill or tough perennials such as garden sage can get away with it, too.

But that leaves a lot of gardeners unaccounted for, including those who grow rosemary, tender lavenders, or other plants that will die if the temperature goes below 15°F, and those who have a yen for fresh herbs all winter. Those people (and I’m one of them) need to make some decisions now.

What Not to Bring In

Perhaps you love all the herbs in your garden equally, and you’d like to bring them all indoors. I suggest you don’t, even if you have a huge house with dozens of south-facing windows.

First of all, forget about the annuals, such as summer savory, chervil, cilantro, borage, and dill. Their lives are about over; if you want them indoors in winter, you can start new plants from seed. I include basil in this group because it’s usually grown as an annual, even though it’s technically a short-lived tender perennial.

Don’t bother bringing in tough perennial culinary herbs whose dried leaves have good flavor—I’m thinking of sage, oregano, and thyme—unless you think you can’t get along without the fresh leaves. Consider the size of the plants, too, and how many smaller plants you could put in their place in front of the window.

Don’t bring in huge tender plants if you don’t have room for them, no matter how badly you need them for next year’s herb garden. (There’s a way around this dilemma, discussed below for pineapple sage.) And if space is limited, abandon tender perennials that are easy to start from seed. Marjoram is a good example—unless you ­absolutely must have it for midwinter salads.

Lastly, turn your back on plants that are diseased or pest-ridden. Even plants that are healthy now can become afflicted in the harsh atmosphere of the indoor desert, but there’s no sense in helping disease and pests get off to a good start there.

What to Bring In

Several plants are worth bringing indoors. I suggest you keep tender perennials on which you’ve lavished special care and affection. These include unusual cultivars, plants of sentimental value, expensive plants such as bay laurel, and herbs that you intend to propagate next spring (such as scented geraniums). And bring in plants that will look great as house plants, such as that prostrate rosemary in the hanging basket.

What about that pineapple sage that smells so good? It’s 4 feet tall and broad, your sunny window is only 3 feet across, and the first frost is going to blacken it permanently. You can save it by taking cuttings right now (see “Disassembling an Herb” on page 60). They’ll root in a couple of weeks and will occupy only a modest space by the window thereafter. If the new plants show signs of taking over the windowsill, take cuttings from them, and so forth, until it’s time to set them outside in the spring, after the danger of frost is past. If you’re not sure about the hardiness of a large perennial plant, you can take cuttings now and winter them indoors in case the original plant doesn’t survive.

What I Brought In

Last September, a couple of weeks before our anticipated first frost, I looked over my herb garden, then looked over my sunniest windows, and tried to predict my craving for fresh herbs in the depths of winter. The herbs I decided I had to bring in included five tender perennials: a big rosemary (Rosmarinus officinalis) I’d started from a cutting two years before, a variegated scented geranium (Pelargonium crispum ‘French Lace’), sweet marjoram (Origanum majorana), a variegated society garlic (Tulbaghia violacea ‘Variegata’), and a Spanish lavender (Lavandula stoechas) that was a gift from a dear friend. I also chose a couple of hardy perennials: a particularly tasty oregano (O. hirtum, sold as O. he­racleoticum) that I had started from seed, and some ordinary culinary thyme (Thymus vulgaris), whose tiny leaves I thought would complement the larger leaves of other herbs while furnishing fresh sprigs for the kitchen. A pineapple sage loomed in the vegetable garden, but I knew I didn’t have a pot or window space for it. I took a few cuttings to winter over indoors and then composted the mother plant.

How I Did It

All the herbs I planned to bring indoors had spent the summer in the ground. The healthy top growth hinted that the roots had also grown significantly, and so it turned out. I’m always surprised to discover how big the root mass gets when it’s not restricted by a pot.

I mixed up a porous potting medium to fill the space in the pots not occupied by the roots and the soil clinging to them. Potted plants need a faster-draining medium than straight garden soil, yet I don’t like to stress the roots by removing all the soil. So I compromise, shaking off some of the soil and putting some porous potting medium in the pot. One key to the success of this method is experimenting to find a watering regime that suits the resulting soil mix in each pot.

To mix the potting medium, I poured equal parts of peat moss, coarse vermiculite, perlite, and compost into my wheelbarrow, stirred them together with a trowel, and dribbled in a little water to dampen it. Peat moss can be very difficult to moisten, but the other substances take up water readily. I like to mix and dampen the potting medium a few hours ahead of time so that it will be uniformly moist when I am ready to use it—just like sprinkling laundry.

I used a shovel to dig out even the small herbs, as it’s much easier on the wrist and forearm than using a trowel. Society garlic grows in a clump as chives do, and when I dug the clump it separated into two pieces. I wrapped the smaller part to take to a friend and potted up the remaining part to keep. The roots of the other herbs I chose to pot up are fibrous, and they stayed more or less in one piece when I dug them.

I chose pots that were slightly larger than the root mass of each herb. The larger ones were terra-cotta, mainly for appearance’s sake. I always advise washing and bleaching old pots before reusing them, but this time I did neither and got away with it. After installing the plants, I watered them thoroughly and moved the pots into the shade of a tree hydrangea.

Acclimatization

The weather was still summery with no cold nights in the immediate forecast. It seemed silly to bring the potted herbs indoors when they could still be growing outside with little attention from me. In theory, though, preparing to bring plants indoors for the winter should begin early and should mirror the hardening-off steps we perform in the spring.

After a week, therefore, I moved the herbs from under the tree to the north-facing front steps, where the light level was lower. I brought them into the front hall on cold nights and returned them to the steps during the day. A frost followed by cold weather cut this routine short after a few days. The herbs came in for good.

Caring for the Plants Indoors

I arranged the pots in the sunniest windows of my dining room, a large, south-facing window and a tall bay window that faces east. The society garlic smelled offensively garlicky for several weeks, especially just after watering, but fortunately the odor disappeared.

As light levels diminished with the approach of winter, the herbs seemed to enter a holding pattern. None appeared to be growing, and only the rosemary offered many leaves for harvesting. I watered only when the soil became dry or nearly so. Sometimes I was a little late, and the pineapple sages wilted on several occasions, but they recovered well after being watered. I applied no fertilizer.

Although the days began to lengthen in late December, the herbs didn’t seem to begin to grow until March. When I noticed the new growth, I started fertilizing the plants occasionally with a dilute solution of soluble fertilizer.

The marjoram showed another kind of growth: little golden aphids sucking the aromatic juices from the new leaves. I sloshed the stems and leaves in a dishpan of Ivory Liquid solution, then rinsed them after half an hour with clear water. This treatment knocked back the aphids, but it doesn’t kill the eggs, so it had to be repeated every couple of weeks as the eggs hatched. Washing the marjoram was easy, but it was a nuisance. One day, I just trimmed off the new growth, and the aphid problem along with it. Interestingly, the aphids never bothered the closely related (but hairy) oregano.

In late winter, a few of the outer stems of rosemary became covered with powdery mildew. I tried dipping each stem into a cup containing baking soda and water. This remedy is said to be effective, and perhaps it is, but I found I preferred the instant cure obtained by cutting off the mildewy tips. The plant is large enough that such pruning wasn’t noticeable.

Putting Them Outside Again

At the end of April, I began hardening off the herbs I had wintered over indoors. I placed the pots close to the east side of the house where they would get morning sun but be out of the wind. Because the nights were mild, I left them outside but was ready to bring them in if frost threatened. It didn’t, and the hardening-off period proved completely uneventful. Two weeks later, with no frost in the forecast, I replanted all but one of the herbs in the ground. The rosemary had outgrown the space it occupied the year before, but I had a huge terra-cotta pot in mind that would accommodate it and some trailing golden nasturtiums. And the cycle continues.

What about Next Winter?

All the herbs I wintered over last year survived the experience, but I’ll be doing things a little differently this winter. For one thing, I’m not bothering with thyme and oregano again. The thyme’s delicate foliage looked stringy, not lacy, and the fresh leaves were tedious to harvest. The oregano sulked until March, and when it finally started to grow, so did the oregano plants I’d left outside in the ground. The leaves were tasty, but for seasoning spaghetti sauce, I found myself reaching for the dried herb—also full of flavor but conveniently handy and ready to use. The marjoram took a while to grow back after its haircut and provided no fresh leaves during this period. Meanwhile, I started some new marjoram from seeds under lights, and the seedlings grew big enough to yield a few fresh leaves before I transplanted them outdoors in May. I won’t be wintering over the marjoram again (unless I have a change of heart at the last minute). The other herbs are still in my good graces and will be repeating the journey they took last year. I plan to treat them all to a shampoo before bringing them indoors.

Providing adequate light in winter is always a problem. The sunniest window gives little light on the many winter days when the sun doesn’t shine at all. The herbs probably would grow better if I kept them under fluorescent lights all winter, but then I couldn’t use them to decorate my dining room as I do now. My plant lights are currently in the basement and a spare bedroom and wouldn’t fit into the decor of the dining room even if I had room for them there. Rotating the plants—keeping them under lights except for special occasions—is another option I don’t think I’ll pursue. Wintering herbs indoors is an exercise in making choices, and I’ve made mine. May your experiences be as satisfying as mine.

Betsy Strauch performs her duties as assistant editor of The Herb Companion by fax and modem from her home in Lenox, Massachusetts, where the New England winters challenge her considerable gardening skills.