Repotting guide

When & how to repot White mountain heather (Cassiope mertensiana)

Also called White mountain heather, Western moss heather, Mertens' cassiope.

More about white mountain heather

About White mountain heather

Cassiope mertensiana · also called White mountain heather, Western moss heather · flowering

White mountain heather is a low-growing alpine subshrub native to western North America, from Alaska to California, found at high elevations near snowfields. Its four-ranked scale-like leaves clothe wiry stems, and it produces delicate white bell flowers on red stalks in early summer. An ideal plant for cool, acidic rock gardens.

Mature size: 10–30 cm tall (4–12 in), slowly spreading to 30–50 cm wide

Watch for — Heat intolerance and summer dieback: Cassiope mertensiana is extremely cold-adapted and suffers badly in warm summers. Temperatures consistently above 20–22°C (68–72°F) cause rapid decline. Position in north-facing aspects, maintain cool root zone with grit mulch, or grow in an alpine house.

How to tell white mountain heather needs repotting

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

Roots growing out of the drainage holes, or the rootball lifting the plant proud of the rim.
Soil that has shrunk away from the pot sides and no longer holds water.
The pot is unstable because the plant has grown top-heavy.
Old, compacted, broken-down mix that stays wet too long — for a succulent that is a rot risk, so refresh it even if the pot size is fine.

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 white mountain heather

Every 2–3 years, into bone-dry mix. White mountain heather's growth habit — low, dense, mat-forming subshrub with four-ranked imbricate leaves on erect to spreading stems — sets the pace. White mountain heather is a low-growing alpine subshrub native to western North America, from Alaska to California, found at high elevations near snowfields. Its four-ranked scale-like leaves clothe wiry stems, and it produces delicate white bell flowers on red stalks in early summer. An ideal plant for cool, acidic rock gardens.

What size pot to step white mountain heather up to

Use a pot only one size up — or even the same pot with fresh gritty mix if the roots have room. White mountain heather stores water and rots in a large pot of slow-drying soil. A tight terracotta pot that dries fast is far safer than a generous plastic one. Never up-pot a succulent by several sizes.

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 white mountain heather

Spring or summer, while white mountain heather is in active growth and warm, is best — roots recover fastest then, and the plant is not sitting in cool damp soil. Avoid repotting a succulent in winter dormancy.

Step-by-step: repotting white mountain heather

Repot dry. Do not water white mountain heather for several days first. Working with dry roots and dry mix dramatically lowers the rot risk for a succulent.
Pick a snug, fast-draining pot. Choose terracotta one size up at most, with a drainage hole. Have gritty acidic, humus-rich, gritty alpine mix ready.
Tip it out and clean the roots. Slide the plant out, crumble off the old soil, and trim any black, mushy or dead roots with clean snips.
Pot into dry mix. Set white mountain heather at its original depth in dry gritty mix, firming gently. Do not bury the stem deeper than it was.
Wait a week before watering. Leave it completely dry and out of harsh sun for about 7 days so any damaged roots callus. Only then water lightly.

Aftercare

Keep white mountain heather completely dry and out of fierce sun for about a week so any nicked roots callus before they meet moisture; watering a freshly repotted succulent is the classic way to rot it. Then resume the normal lean, dry rhythm. Do not fertilise for about 3 weeks — fresh mix already carries nutrients and feeding freshly disturbed roots scorches them.

The right soil mix for white mountain heather

White mountain heather wants acidic, humus-rich, gritty alpine mix. Requires excellent drainage combined with consistent moisture retention — a classic alpine mix of ericaceous compost, coarse sand, and perlite (roughly 1:1:1) achieves this. Target pH 4.5–5.5. Absolutely intolerant of limestone or alkaline conditions. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting white mountain heather — frequently asked questions

How often should you repot white mountain heather?

Every 2–3 years, into bone-dry mix for white mountain heather. Repot white mountain heather every 2–3 years into a snug pot of acidic, humus-rich, gritty alpine mix, ideally in spring or summer. Let it sit in dry soil and do not water for about a week afterwards so any nicked roots can callus. Over-potting and watering straight away is what rots succulents.

What size pot does white mountain heather need?

When is the best time of year to repot white mountain heather?

Should you water white mountain heather after repotting?

No — not straight away. Repot white mountain heather into dry mix and wait about a week before the first watering so any damaged roots callus over. Watering a freshly repotted succulent is the single most common way to rot one.

Should you fertilise white mountain heather after repotting?

Not immediately. Wait about 3 weeks after repotting white mountain heather. Fresh mix already contains nutrients, and feeding freshly cut or disturbed roots burns them. Resume your normal feeding routine once you see new growth.