Today, mushroom compost is generally made from composted straw rather than the traditional well-rotted manure. Once the mushroom farmer is finished with it, the spent compost is often sold direct or through garden centres as a cheap mulch or soil improver.
Spent Mushroom Compost is rich in organic material but, because mushrooms are grown on chalk beds with the compost laid on top, the spent compost is alkaline and therefore not suitable for ericaceous plants. However, for chalk tolerant hedging plants it can be mixed with general compost to make an effective and cost-effective undergrowth mulch. These hedging plants include:
Box (Buxus sempervirens)
Common Beech (Fagus sylvatica)
Euonymus fortunei ‘Emerald Gaiety’
Euonymus fortunei Emerald n Gold
Griselinia littoralis
Hornbeam (Carpinus betulus)
Lavender (Lavandula)
Lonicera (Lonicera nitida)
Photinia Red Robin (Photinia x fraseri ‘Red Robin’)
Privet (Ligustrum ovalifolium)
Rosemary ‘Miss Jessopp’s Upright
Thuja plicata atrovirens AGM
Yew (Taxus baccata)
• Always mix spent Mushroom Compost with ‘standard’ compost to avoid a build-up of chalk in the soil – and remove any larger lumps of chalk before application
• With the growing popularity of spent Mushroom Compost, unused Mushroom Compost is now available. This has a neutral pH and therefore can be applied on most plants – but it does cost a little more
• Do not use on fruit crops or as a top dressing for lawns unless it has been established that the soil is extremely acidic