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Repotting guide

When & how to repot Tansy (Tanacetum vulgare)

Also called tansy, common tansy, bitter buttons.

More about tansy

About Tansy

Tanacetum vulgare · also called tansy, common tansy · herb

Tansy (Tanacetum vulgare) is a tough, aromatic perennial with fern-like foliage and flat clusters of button-yellow flowers in mid to late summer. Pungent and vigorous, it tolerates poor soil and drought, spreads strongly by rhizome, and is classed as an invasive weed in parts of North America. Long grown as an insect-repellent and dye herb.

Mature size: 0.6-1.5 m tall, spreading indefinitely by rhizome

Watch for — Invasive spreading: Vigorous rhizomes form dense colonies and it self-seeds freely; it is a listed noxious weed in some US states. Plant with a root barrier or in a contained bed and deadhead before seed set.

How to tell tansy needs repotting

Repotting on a calendar is less reliable than reading the plant. For tansy, watch for these signs:

For the underlying biology of a pot-bound root system and why it stalls a plant, see our guide to spotting and fixing a root-bound plant.

How often to repot tansy

Pot on seedlings as they grow; not a perennial repot. Tansyis grown for one season, so the question is really “how often to pot on” — keep moving it up before the roots circle. Erect, rhizomatous herbaceous perennial forming spreading colonies of aromatic ferny foliage topped by corymbs of yellow disc flowers; aggressively clonal and can become weedy..

What size pot to step tansy up to

Pot tansy on gradually — a seedling jumped straight into a huge pot sits in cold, wet, airless soil and stalls. Step up one or two sizes at a time as the roots fill each container, finishing in a large final pot or the ground. The aim is roots that never circle and never check.

Not sure of the exact diameter? Our pot size calculator takes the current pot and root spread and tells you the right next size — it deliberately recommends a single step up, never a big jump.

The best time of year to repot tansy

Pot tansy on through the active growing season, whenever roots fill the current container — there is no single date, just "before it becomes root-bound". Avoid potting on during a cold snap.

Step-by-step: repotting tansy

  1. Pot on before it is root-bound. Check tansy regularly; move it up as soon as roots reach the edge of the cell or pot, not after they have circled.
  2. Step up one or two sizes. Choose the next container up — not a giant one. Cold, wet, unused soil around a small root system stalls seedlings.
  3. Knock it out gently. Support the stem, tip the pot, and ease the rootball out without breaking it. A little teasing of circled roots at the base is fine.
  4. Pot into rich mix. Set it into fresh average to poor, well-drained soil at the same depth (tomatoes are the exception — they can go deeper to root along the stem).
  5. Water in and grow on. Water well, keep it in good light, and resume feeding once it is established and growing again.

Aftercare

Water tansy in well and keep it in bright light; a freshly potted-on seedling can wilt for a day while roots settle, so do not overcompensate by drowning it. Do not fertilise for about 1 week — fresh mix already carries nutrients and feeding freshly disturbed roots scorches them.

The right soil mix for tansy

Tansy wants average to poor, well-drained soil. Thrives in lean, dry to medium loam, pH 5.5-7.5. Adapts to roadside gravel and clay; rich soil makes it taller, floppier and even more aggressively spreading. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting tansy — frequently asked questions

How often should you repot tansy?

Pot on seedlings as they grow; not a perennial repot for tansy. Tansy is a seasonal crop, so you pot it on as a growing plant rather than repotting a perennial. Step seedlings up gradually into average to poor, well-drained soil so the roots never circle the cell, ending in a large final container. A root-bound transplant stalls and never fully recovers.

What size pot does tansy need?

Pot tansy on gradually — a seedling jumped straight into a huge pot sits in cold, wet, airless soil and stalls. Step up one or two sizes at a time as the roots fill each container, finishing in a large final pot or the ground. The aim is roots that never circle and never check. Use our pot size calculator to size it from the plant's current pot and root spread.

When is the best time of year to repot tansy?

Pot tansy on through the active growing season, whenever roots fill the current container — there is no single date, just "before it becomes root-bound". Avoid potting on during a cold snap.

Can you put tansy straight into a much bigger pot?

No. Even a fast-growing tansy should only go up one pot size at a time. A vastly oversized pot holds a reservoir of wet soil the roots cannot reach, which stays cold and soggy and rots the roots — the opposite of what you wanted.

Should you fertilise tansy after repotting?

Not immediately. Wait about 1 week after repotting tansy. Fresh mix already contains nutrients, and feeding freshly cut or disturbed roots burns them. Resume your normal feeding routine once you see new growth.

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