Greenhouse Herbs for Year-Round Gardening

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“Every home should be a greenhome–a space for living connected to or wrapped around a greenhouse, a space full of life. It harvests warmth, oxygen, humidity, ions, nice smells, fresh food, and a continuous panorama of vitality.”

–Amory Lovins, co-CEO of the Rocky Mountain Institute, a resource efficiency consulting center near Aspen, Colorado

The gardens at Heartsong Farm in northern New Hampshire host snow well into March, and soil temperatures are too cold for most garden seed germination until early June. Nancy Phillips used to have a three-month season in which to grow more than eighty varieties of culinary and medicinal herbs on 1 acre to supply the town of Lost Nation. But everything changed when she installed a greenhouse ten years ago. “Now I can’t imagine living without one,” she says. “We wouldn’t be able to afford growing at our scale in this climate.”

Phillips’s 10-by-16-foot south-facing lean-to is made from reglazed cypress-framed glass windows salvaged from an 1860s schoolhouse covered with a layer of clear rigid plastic. It relies on its proximity to the house, a small woodstove surrounded by loose bricks and flanked by water containers that hold heat, and an electric space heater (when temperatures dip into or below the thirties) to create a “warming room” that extends the growing season by four months. Four-inch fiberglass batts fill the studded wall cavities, and 10-inch batts insulate the back ceiling. Heating the greenhouse costs Phillips about $15 during March and April, and she burns about a quarter cord of wood, most of it pruned from her apple trees.

The greenhouse nurtures more than just plants. “Going into the greenhouse in March is a balm for my soul,” Phillips says. “It helps me make it through until the crocuses and daffodils start poking up. One of the greatest pleasures is going in there when the rest of the world is covered with snow and my heart is yearning for some green.”

Greenhouses have been much appreciated as climate controllers and ­indispensable additions to the garden and home since Roman times. During the nineteenth century, large steel and glass home conservatories were a sign of wealth in England and America, but with the advent of plastic construction materials, today’s greenhouses come in styles, sizes, and prices to meet nearly every herb grower’s needs.

Green House

Greening the Greenhouse

Greenhouses are versatile. Some growers use them to give herbs a head start. Phillips sows seeds in flats of potting soil in her greenhouse in March, when snow covers the ground outside, but daytime temperatures in the greenhouse may range as high as 90°F on a warm, sunny day. By June, the greenhouse is full of healthy seedlings that are ready for hardening off and transplanting into the garden. Phillips’s favorite medicinals–echinacea, St.-John’s-wort, valerian, nettles, catnip, skullcap, and lemon balm–thrive under this regimen.

Merry Gardens in Camden, Maine, keep its greenhouses working year-round. The nursery offers a wide ­selection of culinary and medicinal herbs along with ornamental ivies, geraniums, and rare tropical plants. Stock plants of perennial herbs spend the winter in a pit greenhouse, a 20-foot-high glorified cold frame attached to the back of a building that is held at 35° to 40°F with a built-in oil furnace. Low light and water, together with the cold temperature, keep the plants dormant through the winter. In January, Beth Jensen, who oversees herb propagation, takes cuttings from the stock plants, brushes the ends of the stems with rooting hormone and antifungal solution, and sticks them in plastic plug trays filled with sand or soil. The trays are placed under shade cloth in a standard greenhouse kept at 50° to 60°F, where a misting system keeps the cuttings moist. Rooting may take as little as a couple of days for some mints to as long as a year for bay laurel. The cuttings are then fertilized with a seaweed-fish emulsion and transplanted into 21/2-inch pots or returned to the pit house to delay growth until they are needed.

The potted herbs are eventually planted in the nursery’s display gardens or sold at the farm stand. Before the first hard frost in October, the cycle begins again. “It’s a real juggling act,” says Jensen. “But it works amazingly well.”

Winter Herbs

“One of the greatest pleasures is going in there when the rest of the world is covered with snow and my heart is yearning for some green.”

From Garden to Kitchen

Jerry Traunfeld, chef at the four-star Herbfarm Restaurant east of Seattle, Washington, has gained renown for his inventive herb-laden dishes (salmon smoked over basil wood with brown fennel Pinot Noir sauce, for example). His herbs come from the Herbfarm nursery, whose five hoop-style greenhouses produce some 600 varieties of culinary and medicinal herbs.

“We could not do this without greenhouses,” says grower Lisa Leckenby. “It’s cold here for nine months of the year. Anything that needs warmth to germinate would not work.”

The temperature in the Herbfarm’s 25-by-40 and 40-by-50-foot plastic-­covered hoop greenhouses is adjusted as necessary to protect the herbs from the cold and to give seedlings a head start. In winter, the hoop houses contain African blue and cinnamon basils, pineapple sage, and lemon scented geraniums (used in lemon sorbet), as well as culinary standbys such as sage, rosemary, and thyme. Marjoram, basil, dill, cilantro, and parsley are started from seed in the greenhouse, then moved out to cold frames or directly to the garden, as spring weather allows.

Melissa Coleman grew up playing in a greenhouse attached to her home in Maine. Now she is a freelance writer in Aspen, Colorado.

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