Gadenin日本語Get the appTwo ways it spreads, and why both matter
Mugwort is listed as a noxious or invasive weed in several regions, and the listing is deserved. It runs underground on thick white rhizomes that travel a foot or more in a season and shoot up wherever they surface, and it also sets an enormous quantity of dust-fine seed that the wind carries well beyond your own garden.
Most spreading plants only do one of those. Barriers stop runners but not seed; deadheading stops seed but not runners. With mugwort you have to close both routes, and the whole of the growing method below exists for that reason.
Before you plant, check what your local authority or extension service says about it. In places where it is regulated, growing it in the open ground may not be permitted at all, and container growing is the only responsible option.
Every fragment of rhizome left in the soil regrows. That is why removing an established clump takes several seasons and why it is far easier never to plant one in the ground.
It belongs in a container
Use a pot of at least three gallons (12 liters), and larger if you want a decent picking plant. Mugwort is vigorous enough to fill that in a single season, so a small herb pot will be root bound by midsummer and the leaves will go tough early.
- Stand the pot up off the soil Rhizomes will find the drainage holes and root straight through into the ground beneath. Stand the pot on a hard surface, a paving slab or a pot foot, and lift it once a season to check nothing has rooted out of the bottom.
- Leave headroom in the pot Fill the compost to about two inches (5 cm) below the rim. Rhizomes creep along the surface and will climb over a rim filled to the top, then arch down onto whatever the pot is standing on.
- If it must go in the ground Sink a solid barrier at least 18 inches (45 cm) deep with the top edge standing two inches (5 cm) proud of the soil, and walk the perimeter every spring. A perforated or overlapping barrier is no barrier at all.
Soil, water and feeding
Mugwort grows on roadsides and waste ground, which tells you most of what you need. It wants sun and free-draining soil and is entirely unbothered by poor ground. The mistake with a container plant is treating it like a pampered herb.
| Item | What it needs | What goes wrong if you overdo it |
|---|---|---|
| Light | Full sun, six hours or more | In shade the stems flop and the leaves lose their scent |
| Compost | Ordinary free-draining potting mix, no enrichment | Rich compost gives soft, sprawling growth that flowers early |
| Water | When the top inch (2.5 cm) is dry | Constantly wet compost rots the crown over winter |
| Feed | None in the first year, a weak feed after the summer cut | Nitrogen produces bulk with far less aroma in the leaf |
| Winter | Cut down, keep the pot on the dry side | A saucer of standing water in winter kills more plants than cold |
The plant is hardy well below freezing and needs no protection. Wet, not cold, is what kills an overwintering pot.
Cut the flowering stems before seed sets
In late summer the plant throws up tall stems topped with hundreds of small greenish buds. They are easy to miss because they are not showy, and by the time you notice them browning they have already shed. Cut every flowering stem down while the buds are still tight and green.
There is a second reason to cut them. Mugwort is wind pollinated and its pollen is a significant hay fever allergen, one of the main late-season triggers in many regions. Removing the flowers before they open protects you and your neighbors as well as your beds.
Bag the cut stems and put them out with household waste. Do not compost flowering stems and do not leave them lying on the soil to dry, because they will finish ripening seed off the plant.
The early summer cut that gives you good leaves
Left alone, mugwort puts everything into height. The lower leaves get shaded, coarsen and turn bitter, and by midsummer there is nothing on the plant worth picking. Cutting the whole clump back hard in early summer, to about a third of its height, forces a flush of soft new shoots from the base.
That regrowth is the best material of the year after the first spring leaves, and cutting hard also delays flowering, which buys you weeks before the seed problem starts. Repeat it once more if the plant runs up again.
What to write down
Two records make every following year easier. Note the date you first see flower buds forming, and note the date of your hard cut. Once you know how many weeks apart those fall on your site, you can time the cut to sit just before budding instead of guessing.
Also mark anywhere you find a shoot outside the pot, with the date. A shoot that appears in the same spot two years running means a rhizome got out and is established there, and that needs digging rather than pulling.