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Repotting guide

When & how to repot Black Medick (Medicago lupulina)

Also called Black Medick, Black Medic, Hop Clover, Nonesuch, Yellow Trefoil.

More about black medick

About Black Medick

Medicago lupulina · also called Black Medick, Black Medic · flowering

Medicago lupulina is a low-growing annual or short-lived perennial legume native to grasslands, roadsides, and disturbed ground across Europe, Asia, and northern Africa, widely naturalised in North America and Australasia. It thrives in full sun on poor to moderately fertile, well-drained soils and, as a legume, fixes atmospheric nitrogen through root nodules — so avoid nitrogen-rich fertilisers. The tiny yellow clover-like flowers turn into distinctive black coiled seed pods that give the plant its common name. It is not considered toxic to cats or dogs.

Mature size: 10–50 cm tall, spreading 20–40 cm wide.

How to tell black medick needs repotting

Repotting on a calendar is less reliable than reading the plant. For black medick, 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 black medick

Pot on seedlings as they grow; not a perennial repot. Black Medickis grown for one season, so the question is really “how often to pot on” — keep moving it up before the roots circle. Low-growing, spreading annual or short-lived perennial with trifoliate leaves and prostrate to ascending stems..

What size pot to step black medick up to

Pot black medick 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 black medick

Pot black medick 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 black medick

  1. Pot on before it is root-bound. Check black medick 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 well-drained, low to moderate fertility 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 black medick 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 black medick

Black Medick wants well-drained, low to moderate fertility. Highly adaptable — grows in sandy, loamy, or clay soils with a neutral to alkaline pH (6.5–8.0); thrives on thin, chalky grassland soils where nitrogen-fixing ability gives it a competitive advantage. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting black medick — frequently asked questions

How often should you repot black medick?

Pot on seedlings as they grow; not a perennial repot for black medick. Black Medick is a seasonal crop, so you pot it on as a growing plant rather than repotting a perennial. Step seedlings up gradually into well-drained, low to moderate fertility 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 black medick need?

Pot black medick 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 black medick?

Pot black medick 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 black medick straight into a much bigger pot?

No. Even a fast-growing black medick 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 black medick after repotting?

Not immediately. Wait about 1 week after repotting black medick. 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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