Growing Herbs Indoors

Interview with Conrad Richter

By James Baggett

Conrad Richter Nothing beats a snippet of fresh herbs from your own indoor herbs to boost flagging spirits in the middle of winter. To get the scoop on growing herbs indoors, we turned to herb expert, Conrad Richter, vice-president of Richters Herbs in Canada.

1. What are some herbs that are especially easy to grow on a windowsill?

Most mints, scented geraniums, rosemary, bay leaf tree, savory, oregano, are some of the easier ones.

2. Which type of container is best? Plastic or terra cotta? Why?

Unglazed terra cotta is better than plastic. The reason is simple: terra cotta allows moisture and air to pass through and plastic does not. That roots need air seems counterintuitive, but they are living tissue and they need to respire just like you and I. If gasses in the root zone are not able to move, the roots will rot. This is what happens when the soil becomes "water-logged": the crevices around the roots become filled with water and the roots cannot breathe, and if the drainage is poor the roots will eventually turn mushy.

Whether plastic or terra cotta containers are used, it is important to make sure that there are drainage holes at the bottom to allow excess water to drain out. If it takes more than a minute for water to begin to drain out of the holes after a thorough watering (to the rim of the container) then you don’t have enough holes or you have a poor draining soil.

3. What sort of soil do you suggest?

Inexperienced gardeners may think that if soil in the garden is good enough to grow herbs or other plants, then the same soil must be good enough for potted herbs. That’s wrong because of the water drainage factor. Good garden soil drains well enough in the garden, but in a container the walls of the container restrict the movement of water in the soil column. Even in unglazed terra cotta containers it is important to use a good potting mix that contains amendments such as perlite or vermiculite or sharp builder’s sand to allow water to move freely.

In our own operation we use an organic potting mix made with compost, peat, and perlite.

4. How much light? Exposure? Water? Fertilizer?

Herbs need as much light as possible, preferably the natural variety from the sun. Direct sunlight, at least four or five hours a day, is the minimum herbs need. Even with that, and with plants positioned close to a south, east or west facing window, I like to recommend supplying supplemental artificial light from growlights.

I often feel that I am battling popular notions about raising plants that are quite wrong. For instance, people often ask, "How many times a week do I water my herbs?" and I will answer bluntly that I don’t know. I always say herbs need to be checked frequently, and only watered if the soil feels dry to the touch. In the winter that might work out to once a week while in the summer that might be once a day. Your finger is a marvelous water meter, so use it to check the soil moisture.

When watering, it is better to water more throughly and less often. A good principle to follow is to water until water comes out of the drainage holes in the bottom of the container.

While many herbs can thrive in poor garden soils, they need decidedly more nutrition when grown in containers. That’s because the container restricts the range of the root system and the plant cannot exploit as much soil volume as it does in the garden. We like to apply a fertilizer such as liquid fish emulsion or a 20-20-20 chemical formulation. Use half the recommended concentration biweekly but only during the periods when the herbs are actively growing.

5. What if pests or diseases become a problem? Do you suggest organic controls?

The main problems on indoor herbs are whiteflies and spider mites, and occasionally, aphids can get out of control, as can mealybugs and scale. For whiteflies, spider mites and aphids, Safer’s insecticidal soap spray works very well. The key is to drench the plants with the spray so every surface of the plants is covered. For aphids and spider mites, I recommend dipping the whole above ground portion of the plants in a bucket of insecticidal solution mixed from the spray concentrate. The great thing about soap spray is that it is harmless to animals and humans.

If you have the misfortune of getting mealybugs or scale, I recommend discarding your herbs and starting with new plants. Organic solutions for mealybugs and scale are not very effective and chemical controls are too nasty for human consumption.

6. Any tips for harvesting? How do you know when it’s time? Is there a best way to snip?

Apart from the higher light requirement, herbs differ from most house plants in one very important way: they have to grow more than just a good show of foliage, they have to grow extra so you can harvest some of it. Unfortunately, indoor conditions conspire to make herbs grow less profusely indoors than out, and one has to adjust expectations accordingly. For example, a basil plant in a sunny garden will produce a quarter-pound of leaves in a single cutting, but a potted basil indoors would soon expire if hacked back that much.

The sooner the herb hacking mindset is replaced by a more delicate and selective pinching mode, indoor herbs stand a chance of surviving through a winter season. Because indoor herbs tend to "reach" for the light and become leggy, it is best to pinch them at the growing tips, thereby forcing a bushier, more attractive growth form. Select sprigs of about one to two inches at the growing branch tips for cutting.

7. Can you eat rosemary with mildew on it?

I have never tried using mildewy rosemary so I can’t attest to the taste, but I would guess that the flavour wouldn’t be much different. To treat mildew, try a mild wash with solution of 1 part hydrogen peroxide (available from the drug store) in 3 parts of water. Weekly or biweekly applications should get rid of the mildew fungus.

8. Are the essential oils in herbs as strong in those grown indoors as out?

Herbs are aromatic because they have essential oils that volatilize to the air. For reasons that are not entirely clear, herbs produce these oils in greater quantity or greater concentration when grown in full sun. In the less abundant light of indoors, aroma and flavour are not as strong but they are still quite acceptable, and for many people almost as good as outdoor herbs.

9. Suggestions for unusual herbs to try indoors?

The Frensham lemon scented geranium is one of my favourites. It gets a little gangly in a window, but the clean strong lemon scent of the leaves is such a wonderful lifter of the spirits in the middle of winter.

Vietnamese coriander is an easy-to-grow substitute for cilantro; it adapts better to the lower light of indoors, and unlike cilantro, it tolerates repeated harvests.

There are many interesting and unusual mints that can grow indoors. Newer varieties such as ‘Sweet Pear’ are worth trying. ‘Sweet Pear’ and ‘Banana’ mints really have scents that resemble these fruits. (Please note that ‘Sweet Pear’ is a trademark name.)

Master Chef Ray Taylor of Toronto just loves our tangerine sage. He cuts the fresh leaves in a fine Julienne and adds them to sauces just prior to serving. Tangerine sage is grown much like the better known pineapple sage which also can be used in the same way.

10. What are some of the ways you use herbs in your everyday cooking?

We are so busy running our nursery these days that we find ourselves experimenting more with using fresh herbs to enhance every day foods. For example, adding finely chopped sprigs of fresh tarragon to store-bought red beet salad gives a really nice twist to an old favourite. We like to use fresh-chopped herbs in salads and on eggs and omelettes, or we’ll throw a few fresh mint leaves in a pot of black tea for fun. For us, it’s much more about having fun with herbs, putting them in unexpected places to add new notes. We are much more apt to throw out the cookbook these days, and fresh herbs seem to be perfectly suited for light-hearted experimentation and fun.

11. Anything you would like to add that I have neglected to ask?

Just make sure that you get the right varieties. There are imposters for tarragon, mint and oregano that are worthless to grow. There are more compact varieties suited for indoor container growing that make better choices than the standard varieties. Make sure that you buy from a reputable herb specialist who can help you select the best varieties for your needs and growing area.

Originally published in Country Living Gardener magazine, February 2001.
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