In short: Coco coir holds little inherent nutrient — you supply everything via fertiliser. Most UK growers use a balanced N-P-K liquid feed (e.g. 10-10-10 or a coco-specific formula), supplemented with calcium and magnesium (Cal-Mag) every 2–4 feeds. Apply at half-strength initially; coir-specific feeds account for the substrate's nutrient behaviour.
One of the most common questions about growing in coco coir is: what nutrients does it need? Unlike soil or compost, coco coir is an inert growing medium — it contains virtually no nutrients of its own. This means you need to supply everything your plants require.
Why Coco Coir Needs Added Nutrients
Coco coir provides physical support, water retention, and aeration for plant roots. Think of it as a sponge rather than a food source. This is actually an advantage: you have complete control over exactly what nutrients your plants receive.
Essential Nutrients for Plants in Coco Coir
Macronutrients (NPK)
- Nitrogen (N): drives leaf and stem growth
- Phosphorus (P): supports root development and flowering
- Potassium (K): strengthens overall plant health and fruit quality
Secondary Nutrients
- Calcium (Ca): essential for cell wall structure. Particularly important in coco coir because raw coir can hold onto calcium. This is why buffered coco coir is recommended.
- Magnesium (Mg): central to chlorophyll production
- Sulphur (S): important for protein synthesis
Best Fertilisers for Coco Coir
Option 1: Coco-Specific Liquid Nutrients
Purpose-made coco nutrients (e.g., Canna Coco A+B, Shogun Samurai Coco) are formulated with extra calcium and magnesium. These are the simplest option with the most consistent results.
Option 2: General-Purpose Feed + Cal-Mag
Use a standard liquid fertiliser and add a separate calcium-magnesium supplement. More flexible but requires more attention to ratios.
Option 3: Slow-Release Granular Fertiliser
For outdoor containers and raised beds, mix slow-release granules (e.g., Osmocote, Vitax Q4) into coco coir at planting time for 3–6 months of steady nutrition.
Feeding Schedule
- Seedlings (weeks 1–3): plain water or quarter-strength solution
- Vegetative growth: half to full-strength balanced NPK feed every watering
- Flowering/fruiting: switch to high-potassium feed
- Frequency: feed with every watering; flush with plain water every 2 weeks
Common Nutrient Mistakes
- Skipping cal-mag — calcium deficiency shows as brown spots on new growth
- Overfeeding — start at half-strength and increase gradually
- Ignoring pH — keep nutrient solution pH between 5.5 and 6.5
- Using soil-only fertilisers — heavy organic feeds can cause issues in coco coir
Coco coir gives you a blank canvas. Pair it with a quality coco-specific nutrient or a balanced liquid feed plus cal-mag, and your plants will thrive.
Our buffered coco coir bricks arrive pre-treated with calcium and magnesium, giving your plants the ideal starting point. Save with our 3-pack bundle.