Regional Gardening Reports :: National Gardening Association

In the Garden:
New England
December, 2008
Regional Report

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Purple sage, marjoram, and thyme enjoy their spot on a sunny windowsill.

Windowsill Herb Gardens

The flurries flying outside my window as I write are a sure sign that winter has finally arrived. Although garden-fresh tomatoes are only a distant dream, you needn't wait until next summer for the taste and smell of fresh basil, thyme, or sage. These and many other common herbs adapt quite nicely to growing indoors.

Although growing herbs indoors is not difficult, it's also not as simple as the coffee table magazines would have you believe -- as you know if you've tried to keep a holiday rosemary topiary as the centerpiece in a dimly lit dining room. It likely shriveled up in a few weeks. But a windowsill garden is another story, and with a little planning and some good cultural techniques, your indoor herb garden will thrive.

Although many herbs will grow in part shade in the garden, indoors you want to give them as much light as possible. A sunny, south-facing window should be adequate for most herbs, but if your window configuration allows, consider setting up grow lights over the plants, too. Winter sun is much weaker than summer sun, and that, combined with the shorter days and the rays having to pass through window glass, means the plants won't get nearly as much light indoors as they would outdoors -- even in a partly shaded spot in the garden.

Overwatering, which can rot plant roots, is the most common cause of houseplants failing to thrive. On the other hand, if your herbs are in small containers they will dry out quickly, especially since most indoor heat sources dry out the air. Check plants every day, and when the soil is dry down to a depth of a half inch or so, water the soil thoroughly.

If the soil has dried so much that it has pulled away from the sides of the container, set the pot in a saucer of lukewarm water so the soil can absorb it through the drainage holes. Once the soil on top is moist, drain the extra water from the saucer. Always check the soil moisture before watering. Too much water can cause the same symptoms -- wilting, dried-out foliage -- as too little water.

Even under the best conditions, indoor herbs will grow slowly during the winter, so adjust fertilizer accordingly. For example, you might dilute fertilizer to one-quarter the recommended strength and apply it weekly. If you choose an organic fertilizer, look for one that's labeled as odor-free.

Types of Herbs
Annuals. Annual herbs, such as basil and dill, will grow for a while, then begin to get straggly. Rather than fighting this tendency, make successive plantings by sowing a potful of seeds about once a month. That way, you'll have a continuous supply of young plants to replace flagging older ones. Although indoor-grown annual herbs won't be nearly as large and vigorous as those that grow outdoors, you'll be able to harvest enough leaves to add some zip to salads or to use as garnish.

Perennials. In fall, pot up small divisions of perennial herbs, such as oregano, marjoram, thyme, and parsley, and take cuttings of sage and rosemary to root. Or purchase small plants. Although it's possible to grow these herbs from seed, it will take a long time for the seedlings to reach a size where you can begin harvesting. I've had mixed results carrying perennial herbs indoors until spring planting time, so don't feel bad if yours don't make it through the entire winter. Just enjoy them for as long as you can.

-- Don't allow foliage to touch cold windows.

-- If you want to plant multiple types of herbs in a single container, make sure they have the same cultural requirements.

-- Learn what conditions each herb prefers. For example, basil prefers warmth, while sage and rosemary like cooler temperatures.

-- Pinch back branching plants, such as basil, to keep them shrubby rather than leggy.

-- Choose compact or dwarf varieties.

Rosemary Topiaries
This time of year you'll find grocery and big-box stores carrying rosemary plants sheared to resemble miniature Christmas trees. Although they look and smell wonderful, know that they will be a challenge to keep healthy indoors. These plants have been grown under greenhouse conditions -- notably bright light and high humidity -- and invariably suffer shock upon being brought into the dimmer, dryer environment of most homes. During the warmer months, you can acclimate the plants to indoor conditions over the course of a few weeks, but this isn't possible when temperatures hover around freezing and plants are intended as holiday decorations. So consider these plants disposable, and if you're lucky enough to have yours survive into the New Year, pat yourself on the back!

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