All of your composting questions answered

1. Can I just put compost on top of soil?

Yes, this method is known as top-dressing or mulching with compost. Simply spread a 2.5–5 cm layer of well-rotted compost directly on top of the soil around plants.

• It gradually improves soil structure as earthworms incorporate it.
• Suppresses weeds and conserves moisture.

🧠 Best used in: no-dig gardening, ornamental beds, and around shrubs.

🔗 Learn more about top-dressing methods from the RHS

2. Can you compost straight into the soil?

Yes — this is called trench composting or in-ground composting.

• Dig a hole or trench 30 cm deep.
• Add your kitchen scraps (vegetable peels, fruit waste).
• Cover with soil and let it decompose naturally.

This method is low-effort and perfect for overwintering garden beds or lazy composting.

🧠 Ideal for: improving poor soil and enriching specific planting spots.

3. Can you put too much compost in a garden?

Yes — too much compost can:

• Lead to nutrient imbalances, especially excess phosphorus.
• Disrupt natural soil biology.
• Cause water retention issues.

Stick to a 5–20% compost-to-soil ratio by volume in most beds. More is not always better.

🧠 Pro tip: Use a compost calculator — see Q12 below.

4. Should you dig compost into soil?

Yes — digging or forking in compost improves soil texture and nutrient content.

• For clay soils: it loosens compaction.
• For sandy soils: improves water retention.

However, no-dig gardeners often prefer applying compost as a surface mulch, allowing worms to do the mixing.

🧠 Best practice: Incorporate 5–10 cm into the top 20 cm of soil before planting.

5. Are tumbling composters any good?

Yes — tumbling compost bins are effective for small gardens and quicker composting.

Pros:

• Faster decomposition (finished compost in 4–8 weeks).
• Easy to turn, well-aerated.

Cons:

• Limited volume so you need to repeat making compost frequently.
• Requires a good balance of greens (nitrogen) and browns (carbon).

🧠 Recommended for: patio composting, beginners, and households with moderate waste.

🔗 Compare tumbling composters at Garden Organic

6. When should I add compost to my soil?

The best times are:

• Spring – before planting.
• Autumn – to enrich over winter.

Avoid applying during frost or heavy rain, as nutrients may leach away.

🧠 Tip: Add compost 2–4 weeks before adding plants or seeds to the area for best integration.

7. Should compost be dug in?

Yes, especially in new beds or poor soil. See Q4 for full details.

8. Should compost be directly on the ground?

Yes — compost heaps and bins can sit directly on soil. This allows:

• Good Drainage.
• Microorganism and worm access from the soil.

Avoid placing composters on concrete or paving unless absolutely necessary.

🧠 Add a layer of twigs at the base to encourage airflow and decomposition.

9. Can I use unfinished compost in my garden?

With caution. Unfinished (or “immature”) compost can:

• Rob nitrogen from the soil while decomposing.
• Contain pathogens or weed seeds.

Only use unfinished compost:

• In fallow areas.
• As trench compost under plants.
• If it’s mostly broken down with no foul smell.

🧠 Never use around seedlings or delicate crops.

10. How to properly compost?

Steps:

1. Choose a good spot: shady, well-drained, directly onto soil not concrete.
2. Layer materials:
   • Greens (veg scraps, grass clippings).
   • Browns (cardboard, dry leaves).
3. Keep it moist: like a wrung-out sponge.
4. Turn regularly: every 1–2 weeks for aeration.
5. Wait: compost is ready when dark, crumbly, and earthy-smelling.

🧠 Avoid including meat, dairy, or pet waste.

🔗 Full composting guide from Recycle Now

11. How do I calculate how much compost I need?

Use this formula:

Length (m) × Width (m) × Depth (m) = Cubic Metres

For example:

• 2m × 3m bed, 0.05m deep (5 cm) = 0.3m³

🧠 1 cubic metre ≈ 1.3 bulk bags or 13 standard 70L bags.

🔗 Online compost calculator

12. Do I need to mix topsoil with compost?

Yes — for best results, mix 30–50% compost with 50–70% topsoil.

• Compost adds nutrients and organic matter.
• Topsoil provides structure and anchorage.

🧠 Pre-mixed blends are available, but DIY mixing offers better customization.

13. Can I fill my raised bed with just compost?

Not recommended. Pure compost:

• Retains too much moisture.
• May lack structure for root support.
• Can be too rich for some plants.

🧠 Ideal mix: 60% topsoil, 30% compost, 10% aeration (e.g., sand or perlite).

📌 Summary Tips

• Use compost as both a surface mulch and soil amendment.
• Apply in moderation — more is not always better.
• Understand the type and maturity of compost before use.
• Use tools like calculators to plan your compost needs efficiently.

Don’t forget if all else fails then Gardening Express sell a wide selection of top quality, great value compost mixes.