Improving gardeners' understanding of water management in peat

RHS project team
Dr Paul D Alexander
Start date
31/01/2010 11:51:42
End date
31/01/2010 11:51:46

Compost, growing media, peat, peat-free

The problem

The RHS believe that the commercial extraction of peat at current rates is environmentally unsustainable. Peat is removed at a much faster rate than it can accumulate, leading to the irreversible destruction of peatlands. This matters because, worldwide, peatlands are important for biodiversity, carbon storage and flood risk management.

Within the UK, horticulture is the only significant consumer of peat using around 3 million m3 per year. Of this total, amateur gardeners consume almost 70% of peat in the UK. This is in the form of growing media, including peat-based and peat-reduced products, purchased from retail outlets as multi-purpose, specialist composts or growing-bags.

Managing peat-free media can require gardeners to adapt their management practices and with this in mind the RHS is conducting research into highlighting areas where management practices need to be altered.


Most growing media (including peat-based) are blends of one or two main ingredients with a small volume of a variety of other materials for specific beneficial properties. The principal materials tend to dominate how growing media perform. In this experiment we seek to understand the watering requirements of different peat-free media in order that they be better managed to produce healthy plants.

Benefits to gardeners

Improving gardeners’ understanding of water management in peat and peat-free multi-purpose growing media.

Summary of results

Peat free growing media have different watering requirements, but once the watering regime has been mastered there is no reason why healthy plants cannot be produced.

Gardeners need to look beyond the appearance of the growing media surface to assess the need for water. Feel the weight of the pot and push your finger in below the surface of the media, both will give you a better idea of the existing water content and whether the plant needs additional water.

Further information

Chosen because of their common use as container plants, Petunia multiflora ‘Prime Time Blue Star’ and Fuchsia ‘Snowcap’ were grown in the summer of 2010. Set out in a randomised and replicated manner, the plants were grown in multi-purpose media either based on peat, wood fibre, coir or composted green waste. Water was applied at five different rates for each medium, the control treatment being optimum watering for that medium, whilst the other four treatments were this value + 25%, + 50%, -25% and -50%. Optimum watering was considered to be when the container was wet through but not waterlogged.

Plant growth and flower number were two of the variables measured. At the end of the experiment a visual assessment of each plant was made, biomass recorded and the compost analysed.

Get involved

The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.