Last updated: April 2015
How do peat alternatives stack up?
Joanna Long talks to Dr. Paul Alexander of the Royal Horticultural Society.
How do peat-based growing media measure up to peat-free alternatives these days?
The enduring appeal of peat has been that it is a very predictable growing medium. It holds water and nutrients well and you know what you were getting from one bag to the next. This is becoming less the case now as lower-quality, cheaper sources of peat can be used to meet consumer demand, which can reduce the predictability of peat-based growing media.
The opposite is happening with peatfree alternatives. Previously these tended to be more unpredictable than peat as they were comprised of materials of variable quality. In the past 10 years, however, the quality of materials has improved and with it, the predictability of peat-free growing media has improved substantially.
Coir is often promoted as a sustainable alternative to peat, but how sustainable is it in practice?
For the UK market, coir is largely sourced from India and Sri Lanka, although it is also available from other areas (e.g. Mexico). The coir used in growing media is actually the dust that remains from the processing of coconut husks being used to produce rope and mat fibres. Although it is often described as a waste material it is now considered by many to be part of the business model and therefore often considered a by-product. Some believe it would be better used to manage and improve local soil quality.
How effective is coir as a growing medium?
Coir is a very good ingredient for growing media. It is important to recognise that no one material on its own works brilliantly. They are all amended to some degree when made into bagged growing media. Peat is made into good growing media by the addition of nutrients, wetting agents and materials like composted bark chips.
Coir is considered by many to be the best propagation material, better even than peat-based materials, due to its fine particle size. This can be a bit too fine for longer-term growing on of plants (1+ years), although as with other products the addition of other materials can help this.
What about the other alternatives on offer, such as household green waste, wool-based growing media and homemade compost?
Composted green waste certainly has the potential to be part of the solution in peat free growing. The problem at the moment is that it can be highly variable from bag to bag and therefore very unpredictable as growing media. This is mainly because the feed material varies (i.e. the material going into the composting process).
Also, some people put anything coloured green in the green waste bin, including glass and plastics, meaning there can be a problem with contaminants or ‘sharps’ ending up in the final bagged product. Some companies are having to hand-sort their feed material in order to address this.So as a growing medium, green waste is still a bit unpredictable, but using it as a soil conditioner is a better way to go.
Wool, like coir, is marketed as a waste material and it does have some potential for growing. However, it can be quite rich and there is the danger that it could damage young growth, so seed germination can be risky. There are several companies working hard to make this a viable product though, and I do hope they are successful.
Home-made compost is a fantastic soil conditioner. There is advice on the RHS website about home composting but my main piece of advice would be to avoid unrealistic expectations and have patience!