St. John's Wort

Sow in spring on the soil surface, and expect no flowers the first year

Pick a full sun to part shade spot with well-drained, coarse-textured soil - this plant does poorly in wet ground. Press the tiny seed onto the surface rather than burying it, and keep it damp through establishment. Seed straight off the plant carries a dormancy that needs roughly four to six months of after-ripening, so use last season's seed or expect a slow, uneven stand. First-year seedlings grow slowly and will not flower or set seed, so your first real harvest is the second summer. The seed is about a millimeter long and needs light to germinate - it does not germinate in the dark - so seed buried in the dark simply banks itself instead of germinating. Fresh seed also needs an after-ripening period of about four to six months before it will come up well.

⚠ Hypericum perforatum is a listed noxious weed in seven US states and spreads by both seed and aggressive rhizomes - check with your state agriculture department or local extension office before planting it, and do not plant it where it can reach pasture, rangeland, or open disturbed ground.

Lay grass litter around the patch to smother the seedling flush

Spread a layer of grass litter or similar fine organic mulch over the bare ground surrounding your planting, and keep competing perennial cover thick right up to the patch edge. A litter covering cuts both germination and shoot extension in this species, and seedling survival is already restricted by competition - bare disturbed soil is exactly the opening its seed bank waits for.

Cut every remaining flower head before the seed capsules ripen

Once you have taken what you want, go back over the patch and cut off every flower head you left behind, before the three-part capsules turn deep reddish brown and split. Cutting several times across the season, rather than once, is what actually stops seed. Bag the cut heads and bin them - do not compost them. A single plant sets roughly 15,000 to 33,000 seeds, and by some accounts they stay viable in the soil for up to 50 years, so one missed season writes a seed bank you will be weeding out for decades.

⚠ The ripe capsules exude a sticky substance that glues seed to fur, boots, and bird feathers - this is how new colonies start down livestock trails, so clean tools and boots before leaving the patch.

Walk a yard out from the clump and dig any new crowns whole

Each spring, check the ground out to about three feet beyond the edge of the clump for new shoots that came up on their own. Lift any you find with the root attached rather than chopping or rototilling through them, and follow the runner back toward the parent plant as you dig. Lateral roots run three feet or more from the parent an inch or two under the surface, and when those roots are injured they push buds that become whole new crowns - so a blade through a runner multiplies the plant instead of killing it.

⚠ Root fragments left in the soil resprout from as deep as two inches, so rake out and remove what you cut loose rather than turning it back in.

Cut the flowering tops while the plant is in full bloom

Take the top several inches of flowering stem - buds, flowers, and the upper leaves together - while the patch is in bloom, which lands near the summer solstice in most of its range. Pinch a petal to check you are on time: the black glands should smear dark red on your fingers. Work with the material fresh for infused oils, tinctures, and pressed juice, and dry the tops if you want tea. Hypericin sits in the small black glands on the flowers, buds, and leaves, so the flowering top is the part worth cutting - the woody lower stem carries little of it.

⚠ Drug interactions are the single most important risk of taking St. Johnswort medicinally, and some are serious - anyone on prescription medication should clear it with a physician or pharmacist first. Hypericin is also a photosensitizer: it blisters light-skinned livestock that eat it and can affect horses on skin contact alone, so keep cut tops and drying racks away from animals.