In medieval times, people thought St. John's wort (Hypericum perforatum) protected them from demonic possession. Maybe they were right. Today, it is widely used to treat mild depression, anxiety, and insomnia, and its antiviral properties are under investigation. It's now so popular that various formulations are widely marketed, but one of the simplest ways to realize its therapeutic benefits is still the old-fashioned way, as an infusion.
Since this herbaceous perennial was brought to New England by European settlers, it has naturalized across much of the continent. It thrives throughout USDA Hardiness Zones 4 through 8 but also grows in zones 3 and 9. In California, Idaho, Montana, and Oregon, St. John's wort grows too well so is considered a noxious weed, and gardeners there cannot buy plants or seeds. In many other regions it is also abundant in woods, meadows, and along roadsides. And gathering from the wild is not considered harmful to the existing population. Before harvesting wild plants, make sure that they have not been treated with pesticides or other chemicals.
The key medicinal constituents are concentrated in the buds, flowers, and upper leaves. A combination of genetic and environmental factors governs their concentration. For instance, narrow-leaved varieties seem to have higher concentrations of hypericin, a key compound, than broad-leaved kinds. But in every case, the level of active chemicals drops dramatically after flowers are pollinated.
Harvest plants while they're in early bloom, after a minimum of four flowers have opened. Snip off the top 8 inches of the shoots, including a mix of unopened buds, flowers, and leaves. Protect them from light, and dry them rapidly to preserve volatile compounds. Dry them for about 10 hours in a warm (86? to 104? F) dark area. Store completely dried herbs in a cool (less than 68? F), dry, dark place for up to a year.
To make an infusion, steep about 2 teaspoons of the dried herb in 5 ounces of boiling water for 10 minutes. Drink it twice a day with food; its effects are not immediate--they may take several months. Some people experience increased sensitivity to sunlight while taking the herb. Before using any botanical as part of a healthcare program, consult a qualified health practitioner. Seeds and plants are widely available.
Shila Patel is a former managing editor at National Gardening.