Potting Composts
Loam/soil-based composts have substance and weight — ideal for large, top-heavy plants. They retain water and nutrients well. The John Innes formulations are most popular. J.I. No.1 is a mix of loam, sphagnum peat, coarse sand and lime/chalk, suitable for young plants. J.I. No.2 has double the loam and lime, and extra fertilizer — for most mature pot plants. J.I. No.3 has treble the loam and lime — for vigorous, bulky mature plants. Good loam is difficult to obtain, so quality of all proprietary loam composts may be variable. Use lime-free composts for acid-loving plants, such as azaleas and rhododendrons.
Soil-less composts were formerly based on peat, but as use of this scarce material is being discouraged, composts based on peat alternatives are now common. Coconut fibre — or coir — is readily available and suitable as seedling, cuttings and potting composts, on its own or mixed with composted bark, farm waste, vermiculite or perlite. They are clean and light to handle, blended with nutrients and water-absorbent.
Multi-purpose composts are a cross between loam-based and other types.
Bulb fibre is based on coir, with oyster shells to reduce acidity, and charcoal to keep it ‘sweet’. It’s clean and free-draining, but as it contains no nutrients, the bulbs deplete themselves and cannot be used again. Bromeliad compost is spongy, very porous and free of lime.
Cactus compost should be free-draining. Add grit, coarse sand or perlite to any proprietary potting compost.
Fern compost should generally be acid, with sand or perlite for drainage and charcoal to keep it sweet. Orchid compost (formerly made of osmunda fibre, peat and sphagnum moss) should be obtained from orchid nurseries.
Perlite is a heat-expanded volcanic mineral which holds water very well and is also free-draining. Vermiculite is a pale, spongy, granular material manufactured from a silicate mineral. It retains a lot of water and air.
Composts should not be firmed with the fingers as this may cause subsequent waterlogging or damage the roots.
Once potted, water the plant, but don’t give it too much — any damaged roots quickly rot if the compost is very wet.
Soil-less composts were formerly based on peat, but as use of this scarce material is being discouraged, composts based on peat alternatives are now common. Coconut fibre — or coir — is readily available and suitable as seedling, cuttings and potting composts, on its own or mixed with composted bark, farm waste, vermiculite or perlite. They are clean and light to handle, blended with nutrients and water-absorbent.
Multi-purpose composts are a cross between loam-based and other types.
Bulb fibre is based on coir, with oyster shells to reduce acidity, and charcoal to keep it ‘sweet’. It’s clean and free-draining, but as it contains no nutrients, the bulbs deplete themselves and cannot be used again. Bromeliad compost is spongy, very porous and free of lime.
Cactus compost should be free-draining. Add grit, coarse sand or perlite to any proprietary potting compost.
Fern compost should generally be acid, with sand or perlite for drainage and charcoal to keep it sweet. Orchid compost (formerly made of osmunda fibre, peat and sphagnum moss) should be obtained from orchid nurseries.
Perlite is a heat-expanded volcanic mineral which holds water very well and is also free-draining. Vermiculite is a pale, spongy, granular material manufactured from a silicate mineral. It retains a lot of water and air.
Composts should not be firmed with the fingers as this may cause subsequent waterlogging or damage the roots.
Once potted, water the plant, but don’t give it too much — any damaged roots quickly rot if the compost is very wet.
