Most gardeners can safely re-use last year’s Multipurpose Compost (MPC) — provided it’s refreshed before planting again.
Simple refresh
- Blend old compost 50:50 with a fresh bag before re-use.
- Or top-up nutrients by mixing in a slow-release fertiliser.
- If it’s compacted, break it up and add a handful of grit or perlite to restore drainage.
- Alternatively, repurpose the old compost as mulch or soil improver around borders.
Soil-building re-energise
- Mix the spent compost with mature homemade compost, garden soil, or a little biochar.
- This re-seeds the medium with microbes and restores the nutrient-cycling capacity that fades during storage or use.
Check the pH: most MPC starts slightly acidic (pH 5.5–6.5) and is balanced with lime during manufacture. After a season, lime and base nutrients wash out and natural acids form — so pH often drops below 6.
- Test a moist sample with a simple garden pH meter or strip.
- If pH < 6, mix in 1–2 tablespoons of garden lime per 10 L of compost and retest after a week.
- Aim for pH 6–6.5 — slightly acidic is perfect for most plants.
- Avoid over-liming, especially for acid-loving species like azaleas, rhododendrons, or blueberries.
When to start fresh
If the compost has gone slimy, water-repellent, or full of roots, it’s time to start again — but even then, it still has value as mulch or soil conditioner.
Explore Soil-Building Approaches →
Summary
Re-using MPC is fine — just restore nutrients, loosen structure, and check pH. Think of it not as “spent compost,” but as a base material ready to be revitalised into living, productive soil.
