Preparing to bring plants indoors for winter should mirror the hardening-off steps we perform in the spring.
Autumn. The harvest of herbs is winding down, and the frenzy of trying to stay ahead of the weeds has abated. It’s easy at this time of year to kick back, 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 can get away with this, and so can those in more rugged climates who only grow annuals, such as dill, or tough perennials, such as garden sage. However that leaves a lot of gardeners unaccounted for, including those who grow rosemary, tender lavenders or other plants that will die at temperatures below 15 degrees, as well as 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 plant, 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 diseased or pest-ridden plants. 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 the next spring (such as scented geraniums). And bring in plants that will look great as houseplants, 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 46). They’ll root in a couple of weeks and will occupy only a modest space by the window thereafter. If the new plants grow rapidly and 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 year, 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. vulgare subsp. 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 also had grown significantly, and so it turned out. I’m always surprised to discover how big the root mass gets when 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 compromised, 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.
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 normally 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.
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 over time.
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 sage 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 diluted 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 I had to repeat it every couple of weeks as the eggs hatched. Washing the marjoram was easy, but 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 of baking soda and water. This remedy is said to be effective, and perhaps it is, but I found I preferred the instant cure of cutting off the mildewy tips. The plant is large enough that such a 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 outside close to the east side of the house where they would get morning sun but be sheltered from 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 terracotta 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 handy and ready to use. The marjoram took awhile 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 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. Even 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 décor 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.
DISASSEMBLING AN HERB
When a tender herb plant is 4 feet tall and wide, and your largest window isn’t, the best way to save it for next spring’s garden is to root cuttings. Pineapple sage (Salvia elegans) is a case in point, and because it roots readily from tip cuttings, it is an excellent candidate for this kind of treatment. If you’re unsure of the winter hardiness of any large perennial herb, such as lavender or rosemary, rooting cuttings provides insurance against losing the plant completely.
The instructions below demonstrate rooting a 5-inch cutting taken from the end of a vigorously growing pineapple sage stem. The rooting medium consists of equal parts peat moss, coarse vermiculite, perlite and compost.
Strip lower leaves from the stem, both to prevent belowground rot and to encourage rooting.
Clip large leaves to reduce the surface area from which moisture is lost.
Rooting hormone, available as powder or liquid at nurseries and garden centers, encourages rooting when used according to package directions.
Make a hole in the rooting medium with a pencil or chopstick, then stick the stem into the hole so that it doesn’t quite touch the bottom of the pot. Firm the soil around the stem.
To minimize moisture loss, set a stiff plastic freezer bag loosely over the pot to form a tent. Place the pot near the window but out of direct sunlight. Condensation inside the bag is a sign of too much sun and/or insufficient circulation. An alternative to this tent method is hand-misting the cutting several times a day.
By the end of two weeks, pineapple sage cuttings will have formed roots; other herbs may take four weeks or longer. Visible top growth indicates that roots have formed. Even though the new roots will now take up moisture on their own, remove the tent or discontinue misting gradually over a few days so as not to shock the plant.
This article originally appeared in the October/November 1993 issue of The Herb Companion.