- Lead scientist
- Dr Paul D Alexander
- Start date
- 2010
- End date
- 2010
- Keywords
Compost, Growing Media, Peat, Peat-free
- Benefits to gardeners
Improving gardeners’ understanding of water management in peat and peat-free multi-purpose growing media
- 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.
- Approach
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.
- Further information
Summer 2010
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 randomized 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.
- Advisory information
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.
- Summary of results
Early findings
The data sets are still being statistically analysed, but early findings suggest that all media tested were capable of producing good quality plants. At the control rate of watering, plants appeared slightly bigger in coir and peat, but leaf colour, size and flower number were good in all four.
In the under-watered and over-watered treatments quality reduced more quickly in composted green-waste and wood-fibre composts.
Peat and coir were able to retain higher volumes of water than the wood-fibre and composted green waste. Good water retention obviously offers greater flexibility as the frequency of watering can be reduced. However as water resources become more valuable, media needing less water to produce good plants could be seen as preferable. Under optimum watering the plants grown in green compost and wood-fibre were still good quality but only received around one third of the amount of water the peat and coir plants received.