St John’s wort, Hypericum perforatum, is a weed of the dry and broken lands. It grows commonly on disturbed and/or degraded land, usually where it is stoney or gravelly or otherwise dry. You often see it along river beds or it appears the year after a new track or road is put in. It also grows extensively on overgrazed land. If you haven’t seen any locally yet look along river beds, in old gravel pits, new tracks or where there’s been any disturbance to the soil.
SJW reproduces by seed, which it produces copiously each year. Once it gets established in an area it tends to spread. I’ve been watching it expand its territory over the past 15 years. In Central it grows everywhere north of Cromwell, and in more select places and along roadsides as far south as Lawrence. It’s in Queenstown, making it’s way into Northern Southland. It grows in river beds and on roadsides in Fiordland (where it first turned up in tourist car parks, presumably having hitched a ride from Queenstown). It’s in places along the east coast where it’s dry (haven’t seen it in Dunedin environs, yet) – it’s in at least some of the east draining rivers.
I’d love to know where it grows in North Canterbury, Nelson/Marlborough and the West Coast, and the North Island.
In some places in Central it’s everywhere. Other places outside of Central it’s more localised, but it’s worth having a good scout around in likely places because it’s still getting naturalised and so hasn’t fully extended its range i.e. it might not be obvious but still there.
Farmers don’t like SJW because it can cause photosensitivity in stock (cattle at least) and a beetle was introduced to try and control it but doesn’t seem particularly effective. There’s a whole lot of bother about SJW causing photosensitivity in humans, but in fact that is rare and seems to be associated with commercial preparations (more on this in the SJW uses post).
SJW is a perennial (meaning it grows back each year from the same plant) but in some ways behaves like an annual – it seeds prolifically and its communities seem to move around a bit. Often a really good patch one year will be absent the following year.
There aren’t too many look alikes to confuse this with (ragwort, Senecio sp, from a distance, which overlaps its flowering with SJW), but here are some keys:
1. flowers are bright yellow and have 5 petals with a tufty centre, and are less than 2cm across.
2. branches and leaves are in opposite pairs.
3. leaves have oil glands, either clear or black, and visible when held up to the light. When crushed these stain the fingers red.
4. flowers also stain the fingers red when crushed.
5. it grows from a central point or clump in the ground and can be a single stalk a couple of inches high up to a largish bush of a metre.
There are other Hypericums in NZ. Tutsan, Hypericum androsaemum, is a garden shrub, but has obviously larger flowers and leaves, no discernible oil glands and generally isn’t considered medicinal because of this (it may have other medicinal properties). There are several native Hypericums, including two that are endemic (they only grow here). I don’t know if the native Hypericums are medicinal but they are rare enough to warrant not harvesting them (especially as the introduced SJW is so common).
I harvest the flowering tops of SJW (including leaves and stalk) for tincture and the flowers for oil. This is an almost perfect sample of what I like to make tincture from. A mixture of flowers and buds with some leaves and stalk, but not really any seed yet. It’s also ok to harvest older plants that have some new seedheads as long as the flowers and buds predominate.
If I was picking for oil I would take most of the top cluster of flowers with as little stalk as easily possible (don’t have to be too pedantic about it), leaving some of the lower buds to eventually produce seed.
Here’s the jar filled with the chopped herb from the basket at the top of the post.
I then filled the jar again, with 50% alcohol, capped it and will let it sit for at least six weeks before decanting.
SJW is famous for going a delicious and intense red as soon as you pour in the alcohol (this photo doesn’t do it justice). Oil takes longer but eventually goes a red colour too.
SJW usually flowers for a month or more. Some years it starts in mid December, but mostly I’ve harvested in January, sometimes even into mid February. It’s still going strong at the moment, some plants are starting to put out seedheads but there are still many in bud and flower. I’m going to make some more oil this week.