Repotting guide

When & how to repot Bog rosemary (Andromeda polifolia)

Also called Bog rosemary, Marsh andromeda.

More about bog rosemary

About Bog rosemary

Andromeda polifolia · also called Bog rosemary, Marsh andromeda · flowering

Bog rosemary is a compact evergreen subshrub native to Northern Hemisphere bogs and tundra. Its narrow, grey-green leaves resemble rosemary and it bears delicate pink urn-shaped flowers in spring. Suited to acidic, permanently moist conditions in rock gardens or bog plantings, it is fully hardy and tolerates challenging cold climates.

Mature size: 15–30 cm tall (6–12 in), spreading 30–45 cm (12–18 in)

Watch for — Phytophthora root rot in stagnant, warm water: Although the plant tolerates wet soil, warm stagnant water in summer can encourage root rot pathogens. Ensure some through-flow of fresh water and avoid placing in low spots that collect warm standing runoff.

How to tell bog rosemary needs repotting

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

Roots spiralling thickly out of the drainage holes or pushing the whole plant up out of the pot.
The pot is so packed that water runs straight through in seconds and barely wets the soil.
It has split a plastic pot, or the rootball is a solid mass with almost no soil left when you slide it out.
Growth and (for bog rosemary) flowering have clearly stalled despite good light and feeding — but remember this plant likes being snug, so a little crowding alone is not a reason to repot.

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 bog rosemary

Only every 2–4 years, when genuinely crowded. Bog rosemary is one of the plants that genuinely prefers a snug pot — it grows and flowers better with its roots a little restricted, so resist the urge to repot it on schedule. Low, spreading evergreen subshrub with wiry stems.

What size pot to step bog rosemary up to

Go up only one pot size — roughly 2–3 cm (about an inch) wider in diameter, no more. Bog rosemary positively prefers a snug pot: it flowers and grows better when the roots are a little restricted. The single biggest repotting mistake here is over-potting — dropping bog rosemary into a pot two or three sizes up. All that surplus soil holds water the small root system cannot use, stays cold and wet, and rots the roots within weeks. When in doubt, choose the smaller pot.

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 bog rosemary

Early spring, just as new growth restarts, is the ideal window for bog rosemary. The plant is moving into its strongest growth phase and re-roots into fresh soil quickly. Avoid repotting in winter dormancy or, for flowering plants, while it is in bud or bloom — recovery is slowest then and you risk dropping the flowers.

Step-by-step: repotting bog rosemary

Confirm it actually needs it. Slide bog rosemary out and check the roots. Only continue if it is genuinely packed — this plant prefers a snug pot, so if there is still soil and room, put it straight back.
Pick a pot only one size up. Choose a pot just 2–3 cm wider with good drainage. Resist anything bigger; over-potting is the main killer here.
Ease it out gently. Water lightly the day before, then tip bog rosemary out, supporting the base. Tease the outer roots free only enough to stop them circling.
Repot at the same depth. Add a layer of fresh highly acidic, peaty, permanently moist, set the plant so the soil line sits exactly where it did before, and backfill around the sides, firming lightly.
Settle it in. Water once to settle the soil, then let it sit. Hold off on more water until the top of the soil dries — fresh soil around a small root system stays wet for a while.

Aftercare

Because the new soil holds more water than the old crammed rootball did, ease right back on watering — let the top of the soil dry before you water bog rosemary again, or you will rot the roots in the very pot you just moved it to. Keep it out of harsh direct sun for a fortnight. Do not fertilise for about 4 weeks — fresh mix already carries nutrients and feeding freshly disturbed roots scorches them.

The right soil mix for bog rosemary

Bog rosemary wants highly acidic, peaty, permanently moist. Requires strongly acidic soil pH 3.5–5.5. In nature it grows in sphagnum moss bogs. Use a mix of ericaceous compost and sphagnum peat (or a peat-free equivalent such as composted pine bark plus coarse acidic compost). Avoid any neutral or alkaline soil or compost. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting bog rosemary — frequently asked questions

How often should you repot bog rosemary?

Only every 2–4 years, when genuinely crowded for bog rosemary. Only repot bog rosemary every 2–4 years, and only when it is genuinely root-bound — it flowers and grows best slightly crowded. Step up just one pot size in spring using highly acidic, peaty, permanently moist. The key mistake is over-potting: a too-big pot stays wet and rots the roots.

What size pot does bog rosemary need?

When is the best time of year to repot bog rosemary?

Does bog rosemary like to be root-bound?

Yes — bog rosemary genuinely flowers and grows best when slightly pot-bound, so do not rush to repot it. The mistake to avoid is over-potting into a much larger pot: the excess soil stays wet, the roots cannot use it, and the plant rots. Only repot every few years and only one snug size up.

Should you fertilise bog rosemary after repotting?

Not immediately. Wait about 4 weeks after repotting bog rosemary. Fresh mix already contains nutrients, and feeding freshly cut or disturbed roots burns them. Resume your normal feeding routine once you see new growth.