The Hypericum genus, commonly called the St. John's wort family, includes more than 400 species of annuals and perennials. They can be shrubs or trees, deciduous or evergreen. Hypericum species vary widely in form -- "Brigadoon" St. John's wort (Hypericum calycinum "Brigadoon"), for example, is a low-growing ground cover that grows in U.S. Department of Agriculture plant hardiness zones 5 through 9, while "Sunburst" St. John's wort (Hypericum frondosum) is an upright shrub, up to 6 feet tall, that grows in USDA zones 6 to 9. Using cuttings for propagation is the best approach for most of these plants, but there are some other viable options, as well.
Although St. John's wort is best propagated from cuttings, it can be grown from seed. The seed is slow to germinate, and the seedlings grow slowly, so you should start them indoors or in a cold frame in fall or winter. Soaking the seeds in hot water can help speed up germination. Transplant the seedlings outdoors in the spring when the plants are at least eight to 10 weeks old.
You can propagate perennial species of St. John's wort from softwood cuttings that you take in the spring. Take 4- to 6-inch-long cuttings from new growth when the stems are still pliable but beginning to turn woody. If the stem snaps when you bend it, it's at the right stage for cutting. Remove the leaves from the lower one-half of the cutting and and plant it in a container filled with growing medium so it can develop roots. Keep the cutting moist and away from direct sunlight until it roots.
Shrubby St. John's wort species can be propagated from either softwood or semi-ripe cuttings in summer. Semi-ripe cuttings come from more mature stems than softwood cuttings -- the stems should be from partially woody, with mature leaves. Root the semi-ripe cuttings in the same way you would root a softwood cutting.
A heel cutting is a type of semi-ripe cutting technique that works well with St. John's wort. To take a heel cutting, pull back a semi-ripe stem so that it peels away from the older woody stem from which it's growing. The cutting will pull a small part of the older stem with it -- this small portion of older wood is called the heel. Root the heel cutting the same way that you root the other types of cuttings. Growth tissue in the heel will help the cutting to produce roots.
Like most perennial plants, perennial species of St. John's wort can be propagated by division. To divide an established plant, dig it up in either spring or fall when it isn't in bloom, divide the root system and replant, mulch and water the divisions immediately.