Commercial compost is a range of products sold in plastic wrapping in garden centres, DIY shops and sundry retailers. This is not to be confused with your own garden compost made from decomposed plant matter.
The contents of these types of commercial compost vary and can affect the growing result considerably. All have a base which has no or negligible nutritional value plus additives that make it useful for a specific purpose.
Typical Compost Constituents – Base
Peat base of small fibers of bog peat is excellent for many purposes but now seen as none ecofriendly due to the over extraction of peat and lack of replenishment of the resource which isn’t sustainable.
Coir as a peat substitute for the base. Coir is made from the hairs & fibers of coconuts and such compost are widely available. There are special organic compost products approved by the vegan society .
Wood pulp based composts and partially composted bark are other bases the industry is trying to develop into retail products but mixes and formulas keep changing
Steralised loam based composts, generically called John Innes after the guy who first formulated them, tend to be heavier.
Composted green waste is becoming popular if you can find a reliable supplier who uses undiseased raw materials
Typical Commercial Compost Constituents – Additives
Most composts are mixes of some of the base ingredients and possibly sand or vermiculite to open up the compost and improve drainage
Fertilisers are added that are appropriate to the end use. seed compost needs less fertiliser than a container planting compost where a plant has to live for at least a season
A wetting agent is often added as peat is very difficult to get wet and you need an even moisture in a pot or seed tray.
Water retaining gels may be added for hanging basket compost.
Typical Compost for Special Uses
Rooting and cutting compost is usually just a mix of sand loam and peat
Seed compost has crushed limestone and phosphates added to help drainage an promote root growth
John Innes No1, 2 & 3 has varying quantities of fertilisers; hoof and horn, superphosphate and potassium sulphate . No 1 Potting Compost is for pricking out young plants, No 2 Potting Compost is for potting on and No 3 Potting Compost is for established plants and shrubs.
Ericacious compost is for acid loving plants like Rhododendrons and lime hating plants like Mahonia and has flowers of sulphur added to the peat based mix.
Cactus compost, Bonsia compost, Orchid compost, Citrus plant compost even African Violet compost are all available from a range of suppliers. One brand with a range available in many outlets is Westland http://www.gardenhealth.com/latest-news.php
Bulb compost used to be called bulb fibre and has no fertiliser . It is used for bulbs like Hyacinths that have already got a store of energy to produce a flower.
Tips On Compost
As it is an organic product the quality can be variable but there will be a brand you like so try some out – currently I am using Arthur Bowers and B&Q own label.
Mix in a bit of grit, sand, vermiculite or water preserving gel depending on how you plan to use the compost
Try keep it uniformly moist.
Add a drop of liquid soap to the water to restrict the growth of moss on seed compost used for slow germinating seeds.
Grow bags contain compost and are a cheaper way of buying compost than small bags.
Compost deteriorates with age so buy fresh compost from a commercial supplier with a fast turnover.