Fertilising guide

How to fertilise White mountain heather (Cassiope mertensiana)— schedule & NPK

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.

Growth habit: Low, dense, mat-forming subshrub with four-ranked imbricate leaves on erect to spreading stems

What fertiliser white mountain heather actually wants — and why

White mountain heather is an acid-loving plant — it can only take up nutrients in acidic soil, so the feed itself matters less than using an ericaceous formula and never liming.

For the language behind the three numbers on the bottle — what nitrogen, phosphorus and potassium each do — see the NPK ratio explained entry. The short version for white mountain heather: match the feed to the job the plant is doing right now, not to a generic “plant food” on the shelf.

How often to feed white mountain heather, and which months

Feeding only earns its keep while the plant is in active growth and can use the nutrients — pour feed into a dormant or low-light plant and it simply builds up as root-burning salt. For white mountain heather:

Very light — apply a dilute ericaceous liquid feed at quarter-strength once in spring. Native to nutrient-poor alpine soils; excess fertilizer leads to soft, rot-prone growth. In practice: an ericaceous feed in spring as growth resumes, repeated through the main growing months; never apply lime, bonemeal or wood ash, which raise pH.

The dormant-season rule matters more than the exact interval: skip feeding entirely when white mountain heather is resting. For the wider context on indoor feeding rhythms across the seasons, the houseplant fertiliser schedule walks through the year month by month.

What strength to mix for white mountain heather

Follow the ericaceous product's own rate — these are formulated for the plant, so the dilution on the label is right for white mountain heather. The variable that actually matters is pH, not concentration.

Feeding always goes onto already-damp soil, never dry roots — water white mountain heather first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the white mountain heather watering schedule.

Signs you are over-feeding white mountain heather

Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for white mountain heather:

Brown, scorched leaf margins from too strong or too frequent a dose.
White salt crust on the soil surface.
Soft, lush growth that fruits or flowers poorly.

Signs you are under-feeding white mountain heather

Yellowing leaves with green veins (iron chlorosis from high pH).
Weak growth, poor cropping and an overall pale, stressed look.
Stunted new shoots in spring despite adequate water and light.

If the symptoms point at watering, light or roots rather than nutrition, the full white mountain heather care brief covers soil, humidity and the common problems for this species.

Flushing and leaching the salts

Flush white mountain heather with rainwater (not hard tap water, which raises pH) if salts build up; better still, mulch with pine needles or composted bark and water with rainwater to hold the acidity.

Organic vs synthetic feeds for white mountain heather

Organic options

Composted pine bark, pine-needle mulch, used coffee grounds and an organic ericaceous feed gently maintain acidity. UK: Vitax or Westland Ericaceous; US: Espoma Holly-tone or Dr. Earth Acid Lovers. Slow, soil-improving, hard to overdo.

Synthetic / liquid feeds

A liquid or granular ericaceous feed — UK: Miracle-Gro Ericaceous, Vitax or Westland; US: Miracle-Gro Acid-Loving Plant Food or Espoma Holly-tone. Pair with rainwater and an acidic mulch for it to work.

Brand names are examples, not endorsements, and UK and US ranges differ — check the label’s own NPK and dilution rate, since formulations change.

Fertilising white mountain heather — frequently asked questions

What fertiliser does white mountain heather need?

An ericaceous (acidic) fertiliser, formulated to keep the soil pH low and supply iron and trace elements in a form acid-loving roots can absorb. Ordinary feeds and any lime lock out iron and yellow the leaves. White mountain heather is an acid-loving plant — it can only take up nutrients in acidic soil, so the feed itself matters less than using an ericaceous formula and never liming.

How often should I feed white mountain heather?

Very light — apply a dilute ericaceous liquid feed at quarter-strength once in spring. Native to nutrient-poor alpine soils; excess fertilizer leads to soft, rot-prone growth. Very light — apply a dilute ericaceous liquid feed at quarter-strength once in spring. Native to nutrient-poor alpine soils; excess fertilizer leads to soft, rot-prone growth. In practice: an ericaceous feed in spring as growth resumes, repeated through the main growing months; never apply lime, bonemeal or wood ash, which raise pH.

What strength of feed for white mountain heather?

What does over-feeding white mountain heather look like?

Brown, scorched leaf margins from too strong or too frequent a dose. White salt crust on the soil surface. Soft, lush growth that fruits or flowers poorly. Feeding white mountain heather an ordinary fertiliser, or growing it in hard tap water / limey soil, is the defining mistake — it triggers lime-induced chlorosis (yellow leaves, green veins) no amount of feeding fixes until the pH comes down.

Should I flush the soil of white mountain heather?