Seed Hut

Fertilisation Guide

Fertilisation Guide: Understanding NPK and Different Fertiliser Types

Proper fertilisation is essential for healthy plant growth, providing key nutrients that support different stages of development. The three primary macronutrients found in fertilisers are Nitrogen (N), Phosphorus (P), and Potassium (K), often represented as an NPK ratio on fertiliser packaging.

Understanding NPK

  1. Nitrogen (N) – Encourages lush, green foliage and strong vegetative growth. Essential for leafy plants and early-stage development. A deficiency results in yellowing leaves and stunted growth.
  2. Phosphorus (P) – Supports root development, flowering, and fruit production. Plants lacking phosphorus often have weak roots and poor blooms.
  3. Potassium (K) – Improves overall plant health, strengthens stems, aids water regulation, and increases resistance to stress and disease. Deficiency can lead to weak growth and scorched leaf edges.

Different plants and growth stages require varying levels of these nutrients, so applying the correct balance is crucial.

Types of Fertilisers and Their Uses

Fertilisers come in various forms, each with its own benefits, application methods, and ideal use cases. They can be broadly categorised into fast-acting liquid fertilisers, slow-release granules, and organic amendments.

Fast-Acting Liquid Fertilisers

These are mixed with water and applied to the soil or as a foliar spray, providing immediate nutrient availability to plants.

  • Best for: Quick correction of nutrient deficiencies, early growth stages, and a rapid boost before flowering or fruiting.
  • Pros: Fast absorption, easy application, ideal for foliar feeding.
  • Cons: Requires frequent application, can leach out quickly with watering.

Use Throughout the Life Cycle:

  • Early Growth: Nitrogen-rich formulas encourage leafy growth.
  • Flowering/Fruiting: A balanced or phosphorus-rich mix supports flower and fruit development.
  • Maintenance: Potassium-rich solutions improve overall plant resilience.

Slow-Release Granular Fertilisers

Granules break down gradually, providing a steady supply of nutrients over weeks or months.

  • Best for: Consistent feeding with minimal maintenance.
  • Pros: Long-lasting, reduces nutrient runoff, requires fewer applications.
  • Cons: Slower results compared to liquid fertilisers.

Use Throughout the Life Cycle:

  • At Planting: Phosphorus-rich granules help establish strong roots.
  • During Growth: Balanced fertilisers ensure steady development.
  • Ongoing Maintenance: General-purpose granules replenish nutrients periodically.

Organic Fertilisers

Organic fertilisers improve soil health by increasing microbial activity, enhancing organic matter, and releasing nutrients naturally. Different organic sources provide specific benefits.

Common Organic Fertilisers and Their Benefits

  1. Compost – Enriches soil with organic matter, improves structure, and provides a range of nutrients.
  2. Manure (Chicken, Cow, etc.) – High in nitrogen, ideal for leafy growth, but should be well-aged to prevent plant burn.
  3. Bone Meal – Rich in phosphorus, excellent for root development and flowering plants.
  4. Worm Castings – Enhances soil structure, promotes beneficial microbes, and provides a gentle nutrient boost.
  5. Fish Emulsion – A liquid source of nitrogen and trace elements, ideal for quick feeding.
  6. Seaweed Extract – Boosts plant resilience, encourages healthy growth, and provides essential micronutrients.

Use Throughout the Life Cycle:

  • Seedlings & Early Growth: Worm castings, compost, and diluted fish emulsion promote steady, gentle growth.
  • Mid-Growth & Vegetative Stage: Manure and nitrogen-rich compost encourage leafy development.
  • Flowering & Fruiting: Bone meal, potassium-rich seaweed extract, and well-balanced compost support blooms and fruiting.

Choosing the Right Fertilisation Strategy

  1. Assess Plant Needs – Fast-growing plants benefit from liquid feeding, while long-term crops thrive with slow-release nutrients.
  2. Adjust for Growth Stages – Use nitrogen early on, phosphorus during flowering, and potassium for overall strength and health.
  3. Avoid Over-Fertilisation – Excess nutrients can cause imbalances, weak growth, or even damage plants.

By understanding NPK ratios, fertiliser types, and organic amendments, you can create a balanced feeding plan that supports plant health from seedling to harvest.

Step-by-Step Guide to Growing Chillies

Growing chillies in the UK requires a good understanding of their needs, as they thrive in warm, bright conditions. Starting indoors gives your plants a head start before the UK’s growing season begins. Follow this detailed guide for best results.

Step 1: Sowing Seeds Indoors (January–March)

1. Choose Your Seeds

  • Pick varieties suited to your space and preferences. For example:
    • Compact varieties: Basket of Fire or Ring of Fire (ideal for smaller spaces).
    • Super-hot varieties: Carolina Reaper, Ghost Chili, or Trinidad Moruga Scorpion.
    • Mild varieties: Jalapeños or Hungarian Wax.

2. Prepare Your Equipment

  • Seed trays or small pots: Ensure they have drainage holes.
  • Seed compost: Use fine, well-draining seed-starting compost.
  • Heated propagator: Maintains consistent warmth for germination.
  • Grow lights: Provide full-spectrum LED lighting (essential for low-light UK winters).
  • Labels: To keep track of varieties.
  • Spray bottle: For gentle watering.

3. Sowing Process

  1. Fill trays or pots with damp seed compost, firming gently.
  2. Sow 1–2 seeds per cell or pot, about 0.5 cm deep.
  3. Cover lightly with compost or vermiculite.
  4. Mist the surface with water.
  5. Place in a heated propagator set to 25–30°C. If unavailable, place pots on a sunny windowsill or near a radiator, but ensure consistent warmth.

4. Provide Lighting

  • Once seeds germinate (7–21 days), move them to a brightly lit area or set up grow lights.
  • Position the lights 10–15 cm above the seedlings and adjust as they grow to prevent leggy plants. Aim for 12–16 hours of light per day.

5. Maintain Ventilation

  • Use a small oscillating fan to circulate air, mimicking natural conditions and preventing damping-off disease. Keep the fan on a low setting and position it away from seedlings.

Step 2: Caring for Seedlings (Late February–April)

1. Watering

  • Keep compost moist but not waterlogged. Allow the top layer to dry slightly before re-watering.
  • Water from the base by placing trays in a shallow dish of water for a few minutes.

2. Thinning and Potting On

  • When seedlings develop two true leaves, thin to the strongest seedling per cell.
  • Transplant seedlings into 7–9 cm pots filled with multi-purpose compost, handling them by their leaves to avoid damage to the stem.

3. Feeding

  • Begin using a weak liquid fertiliser (e.g., seaweed extract) every 10–14 days once the seedlings are established.

4. Monitor Temperature

  • Keep seedlings at 20–25°C during the day and no lower than 16°C at night. Avoid draughts and sudden temperature changes.

Step 3: Hardening Off and Final Planting (May)

1. Hardening Off

  • Gradually acclimatise plants to outdoor conditions over 10–14 days.
  • Place them outside for a few hours each day, avoiding cold winds and direct sunlight initially. Bring them indoors at night.

2. Final Planting Location

  • Greenhouse or polytunnel: Ideal for consistent warmth in the UK.
  • Sunny outdoor spots: Suitable for hardier varieties, provided night temperatures stay above 10°C.
  • Indoors: South-facing windowsills are excellent for compact varieties.

3. Final Pots

  • Transplant into 3–10L pots, grow bags, or directly into greenhouse beds.
  • Use nutrient-rich compost mixed with perlite for improved drainage.
  • Space plants 30–50 cm apart to allow airflow.

Step 4: Ongoing Care (June–September)

1. Lighting

  • If growing indoors or in a shaded greenhouse, continue using grow lights to supplement natural light for 12–16 hours daily.

2. Ventilation

  • Use a rotating fan in greenhouses to maintain airflow and reduce humidity, preventing fungal diseases like botrytis.

3. Watering

  • Water consistently to keep soil moist, especially during flowering and fruiting. Avoid wetting leaves to reduce disease risk.

4. Feeding

  • Switch to a high-potassium fertiliser (e.g., tomato feed) once flowers appear. Feed every 1–2 weeks to encourage fruit production.

5. Pollination

  • Encourage pollination by gently shaking plants or using a soft paintbrush to transfer pollen between flowers.

6. Pest Control

  • Inspect regularly for aphids, whiteflies, or spider mites. Remove pests manually or use organic sprays like neem oil.

Step 5: Harvesting and Beyond (July–October)

1. Harvesting

  • Chillies are ready to pick when they reach their mature colour (e.g., red, orange, or purple).
  • Harvest regularly to encourage further fruiting.

2. Storing

Use fresh or preserve by drying, freezing, or making sauces and jams.