How to Grow Cotton Grass
Eriophorum angustifolium
Cotton grass is a native bog sedge grown for its dazzling fluffy white cotton-ball heads in spring. It needs permanently waterlogged, acidic soil — a bog garden, wildlife pond margin, or container stood in a tray of rainwater all work well. Plant in spring, spacing 30-45 cm apart. Use only rainwater to top up water levels as tap water is too alkaline and will slowly kill it. No feeding, no pruning beyond removing tatty dead stems in early spring. The white cotton heads appear from March and shimmer beautifully until May. Fully hardy and long-lived in the right conditions.
Yearly Lifecycle
Care Essentials
Do not feed. Cotton grass is a nutrient-poor bog specialist — feeding encourages lush growth at the expense of the distinctive cotton heads and can stress or kill the plant.
Watch For
- Drying out — the single biggest threat
- Alkaline soil or tap water
- Invasive vegetation outcompeting in larger bogs
Care Requirements
Light
Full sun to partial shade
Grows best in full sun, which produces the most cotton heads. Tolerates partial shade but flowering is reduced. Avoid deep shade.
Watering
Permanently waterlogged — never let it dry out
Cotton grass demands constantly wet, waterlogged soil. Grow in a bog garden, at a pond margin, or in a container stood in a deep tray of water. Top up with rainwater only — tap water is too alkaline and will kill it over time.
Fertilizing
Never feed — nutrient-poor conditions essential
Cotton grass evolved in nutrient-poor acid bogs. Feeding weakens the plant, promotes rank leafy growth at the expense of the cotton heads, and can kill it. No fertiliser of any kind.
Pruning
Remove dead stems by hand in early spring
No hard pruning required. In early spring, pull away dead and tatty stems by hand before new growth appears. Never cut into healthy green growth.
Growing Tips
Rainwater only
Cotton grass is an acid bog specialist. Tap water is too alkaline and will slowly weaken and kill the plant. Collect rainwater or use pond water to keep the soil permanently saturated.
Keep it permanently wet
This is not a plant that tolerates drying out. The root zone must remain waterlogged at all times. Grow in a bog garden, at a pond margin, or in a container stood in a deep saucer of water.
The white heads are the whole show
The fluffy white cotton heads appear in spring on thin wiry stems and are the plant's main ornamental feature. They shimmer and sway in any breeze and are at their best from March to May.
Plant in groups
A single plant is unimpressive. Plant in drifts of five or more for the best effect — a mass of white cotton heads across a bog garden or pond edge is striking.
