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How To Grow Herbs Indoors

Thyme (Thymus)

Growing Herbs Indoors

Most common herbs can be successfully grown indoors with proper planning and execution. Many people have productive indoor herb gardens using just the light from a southern facing window. The key to success in this manner is having unobstructed natural window light for at least six hours per day. Since natural sunlight through a window is generally only affecting one side of the plant at any given time, it is best to have your herbs in containers in such a way that you can easily rotate them so that all sides of the plant receive their fair share of the light.

Using Plant Grow Lights for Indoor Herbs

If you don't have a south facing window, or perhaps would rather grow your herbs in another area of your home, you couldn't have chosen a better time in history to try your hand at growing herbs indoors.

Thanks to advances in plant grow light technology, anyone can grow a very productive herb garden indoors, using nothing but artificial light.

Without question, the ideal artificial lighting source for herbs commonly available to indoor gardeners would be one of the many fluorescent options, including standard fluorescent tubes, high-output T5 fluorescent tubes and compact fluorescent lamps, or bulbs.

Standard fluorescent tubes, also known as T12 or T8 fluorescents, are the tubes most commonly associated with a standard fluorescent shop light fixture. They are available in 2-foot and 4-foot lengths, and generally hold two individual tubes, although some fixtures can hold 4 tubes. A standard two tube 4-foot fixture will illuminate an area approximately 1 foot wide by 4 feet long. Keep in mind however, that the very ends of a fluorescent tube are significantly dimmer, especially as the tubes age... so the optimal growing area under a 4-foot tube will be 3 feet in length. Using multiple fixtures side by side increases the coverage and provides better coverage by creating multiple points and angles of light to the plants.

Fluorescents are an ideal source of light because they can be placed very close to the light source since they don't produce much heat. Keep in mind that lighting is subject to the inverse square law. How that law works is if you have determined the amount of light reaching an object at a particular distance, than that amount of light will not be halved at twice that distance, rather it will be 1/4 the strength. Since the energy twice as far from the source is spread over four times the area, the intensity is one quarter.

The inverse square law illustrates the importance of placing the artifcial light source as close as possible to the plants without physically damaging them. In the case of standard fluorescents, you should either hang your fluorescent fixtures on chains or be able to raise the plants to a point so that the light source is between 2 and 6 inches above the plant canopy, the closer the better. Since fluorescent tubes burn relatively cool to the touch, the fixture can be placed this close to the plants without physically damaging them. The typical lumen output for a standard 4-foot fluorescent tube is approximately 2400 lumens.

Providing a balanced spectrum of light is of primary importance for success under fluorescents. Virtually all fluorescents are available in differing color spectrum outputs. Standard fluorescents are available in color outputs commonly referred to as "cool white" or "warm white". There are also fluorescent tubes that are color formulated specifically for plant growth. If not using a dedicated "grow tube", you will get best results by mixing one cool white and one warm white tube per fixture.

A better fluorescent technology used for growing plants that is now widely available is known as high output T5 fluorescent. The primary improvement is efficiency. High-output T5's produce almost twice as many lumens of light per watt of energy consumed than standard T12/T8 fluorescent tubes, and due to that improved efficiency, even less heat is output. A typical 45-inch T5 fluorescent tube produces 5,000 initial lumens of light using 54 watts of electricity versus the 40 watts consumed by a standard fluorescent tube producing 2,400 lumens.

The other benefit of high-output T5 fluorescents is the sheer number of fixture options available. Not only are T5 fixtures available in 2-foot (22-inch) and 4-foot (45-inch) approximate lengths, they are available in 2-tube, 4-tube, 6-tube, 8-tube, even 12-tube fixtures of varying widths. These fixtures enable the indoor herb grower to grow herbs in larger areas with more even light distribution than old-fashioned T12 fixtures. The fixtures can be placed further above the plant canopy as well, although it is still recommended that they be placed no more than 12 inches above the plants.

As with standard T12/T8 tubes, high-output T5 fluorescents are also available in differing color outputs, the most common of which are a "day" white (6400-6500K) and a "warm" white (3000K) color. As with standard tubes, most growers blend a mixture of these two color outputs in a fixture to provide as wide a range of color spectrum as possible. However, "day" white tubes are promoted for green vegetative growth cycles while "warm" white tubes tend to promote fruiting and flowering.

Another option is known as CFL, or Compact Fluorescent Lamp. While compact fluorescent lamps of sufficient wattage will work for growing herbs indoors, it is a less than ideal configuration of the light, as the "tubes" are configured in such a way as to provide a single point of light as opposed to spreading the light energy evenly over a broader area as regular and T5 fluorescents do.

Ideally, when using artificial light as the sole light source for the indoor cultivation of herbs, a period of 16 to 18 hours of light per day should be provided on a regular basis. It is easiest to accomplish this scheduling by connecting your grow lights to a grounded 24-hour timer which will automate the daylight hours for your herbs. When using fluorescents to supplement a less than ideal window location, provide at least 12 hours of artificial light.

Indoor Climate Considerations

Comfortable household temperatures are generally fine for most indoor cultivation of herbs, generally between 60 degrees F. and 74 degrees F.

Humidity should be maintained at a comfortable level as well, with extra care being taken during the winter months when forced air heat is operating, as humidity levels will decrease dramatically, causing soils to dry out more frequently and increasing the likelihood of insect pests such as spider mites. Regular misting can keep humidity levels in a desirable range.

Placing a small oscillating fan near the garden and operating it for a couple of hours a day will help your herbs grow shorter and stronger by more accurately simulating outdoor conditions. You don't want a hurricane, just a gentle breeze that causes the herbs to sway slightly for a couple of hours a day is fine.

Preferred Light Levels for Herbs

Varieties that require high light conditions include Anise, Arnica, Basil, Borage, Calendula, Caraway, Catnip, Chicory, Cilantro/Coriander, Dill, Fennel, Hyssop, Lavender, Mustard, Oregano, Rosemary, Sage, Summer Savory, Tarragon, Thyme, and Yarrow. A high light scenario would require plants to be in full overhead direct sunlight for a minimum of 6 hours per day or under T5 high-output fluorescent plant grow lights or HID grow lights for 14 to 18 hours per day.

Varieties that can tolerate some shade include Aloe, Beebalm, Chamomile, Chervil, Chives, Comfrey, Echinacea, Garlic, Lemon Balm, Lemon Verbena, Lovage, Marjoram, Mints, Nasturtium, Parsley, Soapwort, Sweet Cicely, Sweet Woodruff, Tansy, Violet, and Wintergreen. These can also be grown under standard T8/T12 fluorescents at 14 to 18 hours per day, or under T5 fluorescent or HID grow lights for a minimum of 8 to 10 hours per day.