Propagation guide

How to propagate Costmary (Tanacetum balsamita) — step by step

Also called Costmary, Bible Leaf, Mint Geranium.

The best way to propagate costmary

The reliable, beginner-friendly way to propagate costmary is softwood tip cuttings in water or soil. It suits this species because of how it grows: vigorous, rhizomatous clump-forming perennial with long, oval, finely toothed silver-green basal leaves and loose clusters of small yellow button or daisy-like flowers in late summer.. Almost always by division of the rhizomatous clump in spring or autumn, as plants rarely set viable seed in cool climates. Rooted offsets transplant easily.

For the wider picture of which technique suits which plant, our guide to plant propagation methods compares water, soil, leaf, division and offset propagation side by side.

Step-by-step: propagating costmary

Take a tip cutting. Snip a 10–15 cm, non-flowering tip from healthy costmary, cutting just below a leaf pair with clean scissors.
Strip the lower third. Pinch off the leaves on the bottom third of the stem and remove any flower buds — energy needs to go into roots, not blooms.
Root it. Stand the bare stem in water on a bright windowsill, or push it into moist seed compost and cover with a clear bag or dome to hold humidity.
Watch for roots. Roots show in 1–3 weeks. For woodier herbs like rosemary, sage and lavender, soil rooting under a dome is more reliable than water.
Pot on. Once roots are 2–3 cm, pot into average, free-draining loam and pinch the growing tip to encourage a bushy costmary.

The alternative method

If the main route does not suit your plant or setup, direct-to-soil cuttings under a humidity dome is the next best option for costmary. Skip the water glass and root several cuttings directly in gritty seed compost under a clear dome — this is the more reliable route for woody Mediterranean herbs that sulk in water.

Timeline to roots

Realistically: roots in 1–3 weeks; pot up at 3–4 weeks. These numbers assume spring or summer warmth and bright indirect light. In a cold, dark room — or in winter dormancy — the same costmary propagation can take twice as long or stall completely, so do not panic if progress looks slow out of season. Patience beats poking: disturbing a forming root system to “check” on it is a common way to set it back.

Common failure points

Leaving flower buds on the cutting — it spends energy blooming instead of rooting.
Water-rooting woody herbs (rosemary, lavender, sage): they root far better in gritty soil under a dome.
Letting the cutting wilt before it roots — high humidity (a bag or dome) is what carries it through.
Propagating off a stressed, pest-ridden or recently-repotted costmary — always take material from a healthy, established parent.

When to do it

The best window is spring through late summer. Propagation is energetically expensive for a plant, and it only has the spare resources to build new roots when it is already growing actively, warm and well-lit. Out-of-season attempts are not pointless, but expect lower success and a longer wait.

Aftercare

For the first two to three weeks after potting, keep the new costmary slightly moister than you would a mature plant and out of direct sun while the young roots adapt from water (or cutting medium) to soil. Hold off all fertiliser until you see a flush of new top growth — feeding a rootless cutting only burns it. Match the parent's needs as the new costmary settles: Full sun for the most aromatic foliage and best flowering, though it tolerates light shade. In too much shade plants grow lax and leaves are less fragrant and rarely bloom.

Costmary propagation — frequently asked questions

What is the best way to propagate costmary?

Softwood tip cuttings in water or soil is the most reliable method for costmary. Propagate costmary from a 4–6 inch softwood tip cutting. Strip the lower leaves, then root the bare stem in water or moist potting mix in bright indirect light. Roots form in 1–3 weeks and the cutting is ready to pot on at 3–4 weeks. Spring and summer are fastest.

Do you need a node to propagate costmary?

For costmary the rooting structure is softwood tip cuttings in water or soil, so a classic "node" matters less than starting with the right plant material — Strip the lower leaves, then root the bare stem in water or moist potting mix in bright indirect light.

How long does it take costmary to root?

Roots in 1–3 weeks; pot up at 3–4 weeks. Timing varies with warmth and light — propagations move fastest in spring and summer when the plant is in active growth, and can stall almost completely in a cold, dark winter.

What is the best time of year to propagate costmary?

Spring through late summer. Root and shoot development is metabolically demanding, so propagating during the active growing season gives noticeably higher success rates and faster results than attempting it in dormancy.

Can you propagate costmary in water?

Yes — costmary roots readily in a glass of water as long as a node is submerged. Water propagation is the most beginner-friendly route; just move the cutting to soil before the water roots get long and brittle (around 3–5 cm).