Are there alternatives to peat?

Substrate manufacturers, environmentalists and consumers have been dealing with the issue of peat for years. There is a great deal of commitment to find sustainable alternatives for commercial horticulture and hobby gardening.

Around six million cubic metres of peat are processed by German manufacturers every year for producing substrates for garden centres as well as for garden and balcony owners. The raw material from bogs has numerous advantages: It can hold many times its own weight in water, does not decompose in the pot and its high porosity allows plant roots to breathe well. Enriched with fertiliser, sand, clay or lime, it can be used to produce the right substrate for any plant. However, resources are finite and extraction is environmentally controversial. It takes centuries for just one metre of peat to form from decomposed plant parts. There are hardly any new sites available for extraction in this part of the world or they are not allowed to be used.

“But it’s not as simple as some people might think. For one thing, the currently known substitutes are usually not available in the required quantity and quality. Also, they often don’t have the positive properties of peat.” The predominant materials used are compost, bark humus, and wood and coconut fibres.

Peat substitute and reduction

Compost is produced from renewable raw materials such as grass, wood and hedge clippings as well as autumn leaves. It has a low structural stability and is extremely rich in nutrients. It is therefore not necessarily suitable for plants that need poor soil. In contrast, bark humus has a high structural stability and stable pH value like peat, but a significantly lower water storage capacity. It is sourced primarily from the composted bark of coniferous woods, which is obtained during wood processing. Wood fibres also have good air and water permeability. Over time, they decompose and lose their structure. Coconut fibres obtained from the outer layer of the fruit have many of the good properties of peat. Processing usually takes place in Europe because it can be done much more sustainably and with considerably less water wastage than in the source countries. However, the long transport route continues to be a disadvantage.

“The peat-free substrates commercially available today are generally mixtures of the various known substitutes. For hobby gardeners, there is now a whole range of products from different manufacturers. In addition, most of the other garden and balcony soils produced today are peat-reduced formulations. In other words, they are enriched with regionally available raw materials. And this also reduces the overall peat requirement significantly,” says Hückstädt. “These alternatives are also already widely used for commercial horticulture. However, each plant species must first undergo extensive chemical and physical as well as biological and economic testing.” Since reliable information on growing media and potting soils has been scattered or difficult for users to find, IVG and members of the substrates, soils and source materials department developed a substrate book last year. The 250-page work covers individual raw materials with explanations of their chemical and physical properties. It also includes information on the legal requirements that have to be met as well as what internal and external quality assurance looks like. The content is available online free of charge – but only in German.

A relatively new method for the long-term reduction of peat extraction is currently being tested on various trial sites in Lower Saxony. Peat moss is cultivated at these sites. This allows a substrate in crushed, dried form to be obtained, which has comparable properties to mature peat. This project is being carried out with the support of various universities. Test plantings of ornamental plants and vegetables have yielded promising results. However, production and cultivation are still very complex and expensive.

Further information: ivg.org