Greenhouse production methods for herbs are similar to those for greenhouse-grown vegetables. There are some practices, however, that are specific to herb production. Fertility and irrigation, for example, must be managed somewhat differently. Too much water or fertilizer may result in poor establishment of slow-growing seedlings or semi-woody cuttings, excessive growth of species with rapid growth rates, or lower essential oil content, resulting in diminished aroma or culinary value.(10)
Greenhouse temperatures for herb production are about the same as for bedding plants: day temperatures of 70° to 75°F and night temperatures around 60°F. Fast-growing herbs such as basil, chives, and dill become overgrown if started too early.(4) Growth control techniques such as brushing and manipulation of day-night temperatures may be useful. Plugs can be held for a time until sales can begin.
Low light intensity and overcrowding will cause plants to "stretch." In herbs, this problem may be compounded: low light can also reduce the essential oil content. It is important in greenhouse herb production to provide maximum light in late winter and early spring. Eliot Coleman suggests raising winter thyme (mother-of-thyme, Thymus praecox ssp. arcticus), winter savory (Satureja montana), sage, parsley, sorrel, and dandelion for greenhouse production in USDA zones 3 to 6.(4)
Rosemary is raised as potted specimen shrubs, and managed quantitatively over the years by reducing plants to the required number. Photo by Alex Fiore,
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