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Repotting guide

When & how to repot Herb Robert (Geranium robertianum)

Also called Herb Robert, Robert Geranium, Stinking Bob, Red Robin.

More about herb robert

About Herb Robert

Geranium robertianum · also called Herb Robert, Robert Geranium · flowering

Geranium robertianum is a native annual or biennial wildflower of Europe, North America and western Asia, found in woodlands, hedgerows and shaded rocky ground. It thrives in almost any soil in sun or partial shade and self-seeds so freely that a single plant can colonise a border within a season. The most important care fact is to remove unwanted seedlings early while still small, as the taproot toughens quickly. True Geranium species are not listed as toxic to pets by the ASPCA — this species is considered non-toxic to cats and dogs.

Mature size: 20–40 cm tall and wide

How to tell herb robert needs repotting

Repotting on a calendar is less reliable than reading the plant. For herb robert, 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 herb robert

Pot on seedlings as they grow; not a perennial repot. Herb Robertis grown for one season, so the question is really “how often to pot on” — keep moving it up before the roots circle. Sprawling, branching annual or biennial forming loose mounds up to 40 cm across, with deeply dissected aromatic leaves and reddish older stems..

What size pot to step herb robert up to

Pot herb robert 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 herb robert

Pot herb robert 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 herb robert

  1. Pot on before it is root-bound. Check herb robert 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 any free-draining soil — chalk, loam, sand or clay 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 herb robert 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 herb robert

Herb Robert wants any free-draining soil — chalk, loam, sand or clay. Highly adaptable to acid, neutral or alkaline pH. Prefers moist but well-drained conditions; performs well even in poor, thin soils where competing plants struggle. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting herb robert — frequently asked questions

How often should you repot herb robert?

Pot on seedlings as they grow; not a perennial repot for herb robert. Herb Robert is a seasonal crop, so you pot it on as a growing plant rather than repotting a perennial. Step seedlings up gradually into any free-draining soil — chalk, loam, sand or clay 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 herb robert need?

Pot herb robert 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 herb robert?

Pot herb robert 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 herb robert straight into a much bigger pot?

No. Even a fast-growing herb robert 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 herb robert after repotting?

Not immediately. Wait about 1 week after repotting herb robert. 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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