How to Grow Basil Indoors and Outdoors: A Complete UK Gardening Guide
Introduction
Fragrant, flavourful, and surprisingly easy to grow, basil is a kitchen essential that adds depth to dishes like pasta, pizza, pesto, and salads. Whether you have a sunny windowsill or a warm garden bed, basil can be grown successfully indoors or outdoors in the UK—and with the right care, it will reward you with months of aromatic leaves.
In this complete guide, you’ll learn how to grow basil indoors and outdoors, including the best varieties to choose, how to sow and care for your plants, and tips for harvesting and using fresh basil all year round.
Why Grow Basil?
- 🌿 Fresh flavour at your fingertips – Ideal for cooking and garnishing
- 🏡 Grows indoors or outdoors – Suits windowsills, patios, or herb gardens
- 🪴 Low maintenance – Perfect for beginners and busy gardeners
- 🐝 Attracts pollinators – Flowers draw bees when grown outdoors
- 🌞 Quick-growing – Harvest in as little as 3–4 weeks from sowing
Best Basil Varieties for UK Growing
| Variety | Type | Best For |
|---|---|---|
| Genovese | Sweet basil | Classic Italian dishes, pesto |
| Thai Basil | Asian cuisine | Distinct anise flavour, heat tolerant |
| Greek Basil | Compact | Small-leaf, bushy, ideal for pots |
| Lemon Basil | Flavoured | Teas, dressings, desserts |
| Red Rubin | Ornamental | Purple leaves, milder taste |
Tip: Choose Genovese or Greek basil for versatility. Grow multiple types for varied flavour and appearance.
When to Grow Basil in the UK
| Method | Timing |
|---|---|
| Indoors (from seed) | February–August |
| Outdoors (from seed) | Late April–June (after frost risk) |
| Transplanting seedlings | May–June, once nights are warm |
| Indoor growing (year-round)** | With adequate light and warmth |
Where to Grow Basil Indoors and Outdoors
Indoors:
- Bright windowsill – South-facing ideal
- Conservatories or greenhouses
- Grow lights or LED strips can extend growing in low light
Outdoors:
- Sunny, sheltered spots
- Raised beds, herb gardens, or patio pots
- Avoid cold, windy areas or heavy shade
Temperature tip: Basil prefers 18–30°C. It will suffer below 10°C.
How to Grow Basil from Seed: Step-by-Step
Step 1: Sow the Seeds
- Fill small pots or trays with seed compost
- Sow seeds thinly on the surface
- Cover lightly with fine compost or vermiculite
- Water gently and place in a warm spot (20–25°C)
- Germination takes 5–10 days
Tip: Use a heated propagator for best results.
Step 2: Potting On or Transplanting
- Once seedlings have 2 sets of true leaves, thin or transplant to larger pots
- Space plants 15–20cm apart
- Harden off outdoor basil by gradually acclimatising to outside over 7–10 days
Step 3: Choose the Right Container (For Indoors or Patios)
- Use pots 15–20cm wide and 15cm deep
- Ensure good drainage – add grit or broken crockery at the base
- Use multipurpose compost with added perlite for airflow
Caring for Basil Plants
Watering:
- Keep soil moist but not soggy
- Water at the base—avoid splashing the leaves
- Water early in the day to prevent mildew
Feeding:
- Feed every 2–3 weeks with a diluted liquid feed
- Organic feeds like seaweed extract or tomato fertiliser work well
Pinching and Pruning:
- Regularly pinch off the top leaves to encourage bushy growth
- Remove flower buds to prevent the plant from going to seed
- Don’t harvest more than a third of the plant at once
Growing Basil Indoors Year-Round
Basil can be grown indoors all year with proper care.
Indoor Growing Tips:
- Place on a sunny windowsill (south or west-facing)
- Rotate pots to ensure even growth
- Use LED grow lights if natural light is limited
- Maintain room temperatures above 15°C
Common Indoor Problems:
| Problem | Solution |
|---|---|
| Leggy growth | Provide more light or pinch tips regularly |
| Yellowing leaves | Check watering—avoid overwatering |
| Pests (aphids, gnats) | Spray with water + neem oil or use sticky traps |
Growing Basil Outdoors in the Garden
Planting Out:
- Wait until all risk of frost has passed
- Space plants 20–30cm apart
- Plant in full sun with shelter from wind
Outdoor Care Tips:
- Mulch around plants to retain moisture
- Water in the morning to reduce leaf diseases
- Protect from slugs and snails using collars or barriers
Companion Planting with Basil
Basil is not only a culinary favourite—it’s also great in the garden.
Good Companions:
- Tomatoes – Improves growth and flavour, deters pests
- Peppers – Similar growing needs
- Marigolds – Repels aphids and whiteflies
- Lettuce – Shaded by basil’s bushy leaves
Avoid Growing Near:
- Sage or rue – Compete for resources
- Mint – Can be too invasive for shared pots
Harvesting Basil Leaves
When to Start Harvesting:
- Once plants are 15–20cm tall and bushy
- Start harvesting 4–6 weeks after sowing
How to Harvest:
- Pinch leaves from the top of the plant
- Always leave a few sets of leaves below
- For best flavour, harvest in the morning
Storing and Preserving Basil
Use Fresh:
- Wash gently and pat dry
- Add to dishes just before serving
- Sprinkle over salads, pasta, pizza, or sandwiches
Preserve for Later:
- Freezing: Chop and freeze in ice cube trays with olive oil
- Drying: Hang small bunches in a warm, dry room (flavour is milder)
- Pesto: Blend with garlic, pine nuts, cheese, and oil and freeze in portions
Common Basil Growing Problems and Solutions
| Issue | Symptoms | Fix |
|---|---|---|
| Downy mildew | Yellow leaves, fuzzy undersides | Improve airflow, avoid overhead watering |
| Bolting | Rapid flowering, poor leaf growth | Pinch flowers, harvest more regularly |
| Slugs/snails (outdoors) | Chewed leaves | Use barriers or night patrols |
| Fungal rot | Stem base rots, wilting | Avoid waterlogged soil, improve drainage |
| Leggy growth | Tall, weak stems | Provide more light, pinch to bush out |
Growing Basil for Seed Saving
Let one or two basil plants flower and go to seed.
- Allow flower spikes to dry on the plant
- Collect seeds and dry them thoroughly
- Store in an envelope in a cool, dry place
- Use next year for a fresh crop!
Conclusion
Whether grown on a windowsill, balcony, patio, or garden bed, basil is one of the easiest and most rewarding herbs to grow in the UK. With the right warmth, light, and care, you can enjoy an endless supply of fresh basil leaves from spring through autumn—and even year-round indoors.
By following this step-by-step guide, you’ll be able to grow lush, healthy basil plants that keep your kitchen stocked with flavour and your garden filled with delightful fragrance.
Top 10 Questions and Answers About Growing Basil Indoors and Outdoors
1. Can I grow basil indoors all year?
Yes! Use a sunny windowsill or supplement with grow lights in winter.
2. When should I plant basil seeds?
Sow indoors from February onwards, or outdoors after the last frost in late spring.
3. How often should I water basil?
Water when the top inch of soil is dry—basil likes consistent moisture.
4. Does basil need full sun?
Yes—6–8 hours of sunlight daily is ideal for healthy growth.
5. Can I grow basil in pots?
Absolutely! Use a 15–20cm pot with drainage holes and rich compost.
6. Why are my basil leaves turning yellow?
Usually caused by overwatering, poor drainage, or nutrient deficiency.
7. How do I keep basil from flowering?
Pinch off flower buds as soon as they appear to prolong leaf production.
8. Can I grow basil with tomatoes?
Yes—basil is a classic companion plant for tomatoes in pots or garden beds.
9. How do I harvest basil without killing the plant?
Always harvest from the top, leaving several leaves below for regrowth.
10. How do I preserve fresh basil?
Freeze in olive oil, make pesto, or dry for long-term storage.