It was never my intention to grow horehound. Not that I had anything against the plant, but there you are.
My wife and I first encountered horehound growing wild along the Hassayampa River, in a nature preserve maintained by The Nature Conservancy. We had become involved as volunteers, and spent our weekends one summer (during our first year of marriage) clearing trash and cutting trails for future visitors. Being interested in natural history we were curious about the many plants and animals we saw there, and did our best to learn as about as many of them as we could. Among the first plants we identified was a compact, shrubby herb with a whitish, fuzzy look to it called horehound. Our inquiries prompted the local naturalist to say it was originally from Europe, brought here by colonists as a medicinal herb. As has been the case with many plants brought to North America - deliberately or not - horehound found the continent to its liking, becoming naturalized from coast to coast.
That would have been the end of the matter for us, a little botany and a little lore, if the herb had not followed us home. And even then it would only have been a weed - a curious weed, having used us to disperse itself into the Phoenix metro area, but still just a weed, soon to be removed from lawns and gardens. We did not get around to removing it immediately, and then it bloomed, and we found a reason to let it grow.
It made the trip from Wickenberg, Arizona (site of the Hassayampa Preserve) to Phoenix because of the little hooked teeth on its tiny, brownish fruit. We found, on nearly every visit, that we had socks thick with these little oblong burrs. Not thinking, we stripped them off and tossed them into the compost pile along with the other debris that managed to come home with us. The compost we later harvested was spread over the lawn and the vegetable garden. As luck would have it (good luck, as it turned out) the seeds did not succumb to the composting process. The following spring we had little gray weeds popping up in a number of locations.
Horehound is a distinctive plant, even when young, so we recognized it immediately. The stems and undersides of the rounded, corrugated leaves are thick with white hair. The plant would be a dark green without the hairs, but with them is transformed into a soft grayish-green, upright plant that branches repeatedly from the base. It isn't an unattractive plant, even though its flowers - tiny white blossoms in tight knots around the stems, at the leaf nodes - are anything but showy. (In fact, like many other members of horehound's family, the mints, you need to look closely to see them at all.) But we don't grow it for its looks.
The name horehound, to believe the most commonly publish explanation, comes from this grayish appearance. Many of the references I've used state that horehound is a misspelling of hoarhound, with the prefix hoar referring to the grayness of the plant, as in hoar frost, or being gray and hoary with age. At least, this explanation worked for an elder neighbor who, upon being told the plant was called horehound, raised her eyebrows and look a bit concerned. (She was relieved to learn the name was not spelled with a "w.") The scientific name for horehound is Marrubium vulgare, and like all such binomials, tells you something about the plant when the name is translated. Marrubium is the Latinized version of the Hebrew name for horehound, marrob; horehound is one of the five bitter herbs of Passover. Vulgare does not mean there is something uncouth about horehound; in Latin it means, simply, common, a reference to the fact that horehound can be found in many parts of the world. Those little hooked teeth on the fruit are a really effective dispersal mechanism, as plant ecologists call such things.
The ancient Hebrews who picked horehound for Passover knew what they were doing, since bitter is certainly a word that could describe the taste of unadulterated horehound. The Navajo name for the plant is azee'nidoot'eezhii libahigii, which translates to something like "gray-knotted medicine," and is supposed to refer to the appearance of the plant. And the clumps of flowers packed around the stem do sort of look like fat knots on a length of gray cord. Having tasted a decoction of horehound prepared by an herbalist friend, I find myself wondering if the Navajo name actually doesn't describe the look and color of the face of the herbalist's patient! (This could explain why honey is so popular with herbalists.)
The last part of the name is supposed to come from a time when horehound was considered to be effective protection from the bite of a rabid dog. For myself, I would prefer any species of tall, tall tree to horehound, in such a situation.
A curious set of names for a curious plant, and like most plant names the stories behind the names are as interesting as the plant. But interesting as all this might be, that isn't why I grow horehound, either.
Nor are its reputed medicinal uses my motivation for keeping it in my garden. Horehound as a medicinal herb has a truly venerable tradition behind it, with written records of its use going back at least as far as Claudius Galen, the physician of Roman Emperor Marcus Aurelius. And since Claudius Galen did not claim to have discovered horehound's medicinal value, it must have been known for a long time before he got his hands on it. Galen recommended its use in the treatment of respiratory infections as an expectorant, and although it has been claimed that horehound is effective in treating maladies as varied as malaria, hepatitis, and constipation, the treatment of clogged lungs remains its best known use. And there is no shortage of people who swear by the stuff in this capacity (the FDA's poor opinion of horehound to the contrary notwithstanding). Check out any book on herbalism and you will find no shortage of recipes and recommendations concerning the use of horehound. My herbalist friend was trying to help me get past a nasty chest cold when she gave me horehound; I did not have a garden then and had not yet seen a living horehound plant, just dried and crumpled leaves. Even with honey mixed in I found it unpleasant (azee'nidoot'eezhii libahigii!!) to drink. But being an opened-minded sort, I tried it anyway. Did it work? Well, I got better, but since I suspect I would have done so anyway there is no way to judge how much the horehound helped, or if it had any effect at all. But since I don't grow it as a medicinal herb, it really doesn't matter.
If not for looks, curiosity (okay, there's a bit of that, or was in the beginning), or medicine, why bother to grow horehound? You don't cook with it, that I have ever heard of, although I'm told it can be used as a substitute for hops in the brewing of beer. (What a strange brew that must be. I wonder if the medicinal value of the herb survives the brewing? Hmmm. . .) No, I grow horehound for the most practical of all gardening motives, pest control. Like many of its cousins in the mint family, horehound's many tiny flowers attract parasitic wasps and flies in great numbers. When horehound first bloomed in our yard we had just begun to embrace the ideas of "organic" gardening, and of these principles one of the most fascinating to us was the idea of employing naturally occurring, beneficial insects for pest control. Grow herbs and such with tiny flowers, the books told us. And here we had one, by accident, that was attracting clouds of Braconid and Ichneumonid wasps, Tachinid and Syrpid flies. These insects, in their larval forms, parasitize or otherwise consume many other insects that we find pestiferous. Any plant that attracts them is worth growing, and in this capacity horehound has few equals. It is a hardy plant, capable of growing where many garden plants fail to thrive. It survives all but the harshest winters, and even then reseeds itself very effectively. It also blooms over a long season, attracting beneficials almost as long as you are likely to need them.
You can get started with horehound, for whatever purpose, easily enough. The seeds are available in most catalogs that sell a good variety of herb seeds, and in my area at least, horehound transplants show up in the local nurseries on a fairly regular basis. Plant the seeds when it is warm enough, cover them lightly with soil, and keep them moist. You know, the usual stuff you do to plant seeds directly in the garden. Horehound is not fussy about soil, so you can distribute the seed along garden edges and in odd, uncultivated corners, with good results. Die-hard seed starters can sow the seeds indoors for an early start, but unless your growing season is measured in weeks - with single digits! - I wouldn't bother. Here in the Desert Southwest horehound can handle full sun, but really appreciates some shade, especially in the afternoon. It grows wild here in riparian areas such as the Hassayampa River Preserve, where it thrives in dappled shade at the feet of cottonwoods and willows. In more northern regions full sun should suit it.
For best results in attracting beneficials, use horehound directly as a companion plant. Tomatoes, for example, are said to be "encouraged" by growing horehound nearby. The encouragement, in this case, is the host of tiny wasps and flies drawn to the horehound flowers, who then mate and spread out through the garden in search of suitable hosts for their eggs. And guess what they find right next door? Tomato plants that were recently visited by a hawk moth, which is to say the adult form of the dreaded tomato hornworm. These little hunters are good at what they do, and few hornworms will escape their notice. Sickly hornworms do not put much pressure on your tomatoes; encouragement indeed! And of course, this all holds for peppers and other garden variety members of the Potato family.
You could also gather your own seeds in the wild just as easily. (In fact, if you enjoy the occasional walk in the woods, you may not be able to help but gather some seeds.) Horehound plants in the fall and winter have hard, prickly-feeling knots on the stems were the flowers bloomed. These are masses of small, urn-shaped fruit that contain, on average, three or four seeds each. Strip these from the plant (wear gloves) and crumble them over the area where you want the horehound to grow, then treat them like any other planting. You should thin the seedlings until they are about one foot apart.
However you get horehound started, you will find it an undemanding plant. In fact, it grows like a weed. Whatever soil improvement works for your tomatoes or peppers will suit it fine. The more water it receives, the more it will grow and bush out. I have seen horehound plants in the wild that were three feet tall and a couple of yards across. Such a monster is unlikely to be seen in a garden (unless you deliberately encourage it to go berserk), but if size becomes a problem, simply trim the horehound back. Trimming is also a good idea at the end of the season, if you want some control over where horehound grows for you. Every cat or bird that comes in contact with your horehound will disperse some seeds for you, if you don't trim the plants of their spent flowers; those little prickly hooks again, in action. Cut off the stems with the seed clusters and leave the lower stems; new growth will come up in the spring, if you are leaving it as a perennial. (In really cold areas, throw a little straw or some other mulch over the plant.) If the plan is to start fresh, keep a few of those knots of seed in a cool, dry place until next spring.
Companion plant, medicinal herb, tough and durable, ruggedly handsome, horehound is worth growing, no matter what motivation leads you to plant it.
About the Author Thomas Watson is graduate of the University of Arizona College of Agriculture, where he earned a BS in Agriculture, majoring in plant sciences. When he is not writing he is usually working in the garden, re-landscaping his Tucson home, studying botany and plant identification, or "out there" somewhere, studying the natural history of the Sonoran Desert. This is all, of course, based on the assumption that it isn't baseball season, in which case he'll get all of the above done before the next Diamondbacks game.