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Gardening: Growing herbs indoors

Hang in there, gardeners — there is hope. Growing herbs indoors will not only keep your green thumb flexible but fresh herbs are an excellent addition to your home-cooked meals on a cold winter day.

One of the biggest challenges when growing food plants indoors is providing enough light. Whenever possible, locate your plants on a south or west facing windowsill. If this is not an option, you may need to provide some supplemental light.

Plants require a variety of wavelengths of light to grow. Traditional greenhouses use high pressure sodium lamps (HPS) that provide a full spectrum of light. HPS lights work very well for growing plants indoors, but they are expensive to operate and also produce a lot of heat. Plants and flammable objects must be kept an appropriate distance from HPS lights to prevent plant damage and fires.

More commonly, indoor growers use fluorescent lights for growing plants. Purchase fluorescent tubes that are produced specifically for growing plants, as these lights will provide the proper light wavelengths for plant growth. Fluorescent lights do not produce much heat and should be placed 30-45 cm above seedlings and turned on for 14-18 hours/day. To test if lighting is adequate, the shadow cast on a white piece of paper at midday by an object 10-15 cm above the paper should have a definite outline.

LED lights are the newest light technology. Initially, they would only emit one or two very specific wavelengths of light; this is not sufficient to grow healthy plants. However, LED light technology is improving. There are some lights available with multiple wavelengths and they are the cheapest lights to operate. If you decide to use LED lights, choose ones recommended for plant growth that have a wide range of wavelengths available in the bulbs. Don’t be surprised if your plants seem to struggle under the LED lights.

Some herbs take a long time from seeding to harvest. Bringing herbs that were growing in your garden indoors is possible, as long as they are inspected for diseases and pests. Avoid bringing diseased plants indoors. Dig roots with some soil surrounding the roots and use an indoor potting mix. Garden soil does not drain well in pots and will encourage fungal diseases.

Trim plants to half their height; this will encourage new growth and help to reduce insects that might be hiding in the foliage. Parsley and chives are two herbs that can be ‘split’ from the main garden plant by taking some roots and leaves and planting them in a container.

Some herbs will root well from a plant cutting. A piece of the stem and some leaves are cut from the ‘mother’ plant and rooted in moist growing media. Marjoram, mint, rosemary and tarragon can be propagated this way.

Basil, cilantro/coriander, dill, oregano, sage, summer savory and thyme all grow well from seed. Herb seeds prefer warmth and moisture to germinate. Some herb seeds, like basil, are very tiny and should only be buried lightly. Marjoram seeds require light to germinate and should not be buried.

Cilantro/Coriander is a fast growing herb that germinates well from seed. It will bolt (flower) very quickly, so plan to succession-seed this herb several times throughout the winter.

Sorrel and lovage are larger perennial herbs. They can be grown indoors but will need a one-litre pot as a minimum for each plant.

If you are new to indoor herb gardening, try growing just one or two of your favourites for the first year. If you are an experienced indoor grower, challenge yourself with a couple of new herb selections. I once read in a UC Davis newsletter that there are more than 600 different varieties of mint in the world. Happy gardening!