Hypericum perforatum, more commonly known as St. John's wort, is a perennial flowering herb that can reach up to 3 feet in height. The plant is most valued for its numerous medicinal properties, but it also makes a wonderful addition to the home garden. Bright yellow, saucer-shaped flowers bloom throughout summer, although they may not appear in the first season after planting. Hypericum is well-suited to meadows, woodland gardens or borders, and requires only minimal care to thrive.
Sow Hypericum perforatum seeds indoors in late winter, at least three months before the last frost in your area. Sprinkle the seeds on top of sterile seed-starting mix and lightly cover with no more than an eighth inch of the mixture. Keep the growing medium moist by watering from the bottom about once per week, but do not allow it to become soggy or wet.
Place the growing container in an area that receives bright, indirect light for most of the day and keep the temperature around 50 to 55 degrees Fahrenheit at all times. Germination will occur in one to three months if temperature, moisture and light requirements are maintained.
Plant hypericum perforatum seedlings outdoors in a sunny location with well-drained, average soil after all danger of frost has passed. Hypericum will grow in partial shade but produces more blooms in full sun. Avoid planting in full shade. Space plants 8 to 10 inches apart to allow room for growth.
Water hypericum perforatum plants once every seven to 10 days to keep the soil evenly moist, or anytime the top few inches of soil feel dry to the touch. Increase watering to twice per week during extended dry periods or in very warm climates. Reduce watering in fall and winter, when the plant begins to enter dormancy or dies back.
Feed hypericum perforatum once in spring and once in summer, but only if grown in poor soil. Plants grown in fertile soil rarely need supplemental feeding. Use a balanced all-purpose fertilizer according to the manufacturer's instructions, and water thoroughly after application.
Apply a 2- to 3-inch layer of mulch around the base of hypericum perforatum plants in fall before the first frost. This will help insulate the roots through cold winters. In warmer climates, mulching might be unnecessary for insulation but it can help retain moisture and prevent the growth of weeds.