So how do you build a sphagnum farm?

29 May 2020 - Published by Harry Mach
Farming moss might seem easy. The CANAPE project manager’s garden certainly has quite a lot growing without any human intervention. However, to produce a marketable quantity of crop, things are a little more complex.

Our field in Barver, Diepholz, Lower Saxony sits on the edge of an area of land proposed for restoration. In the other direction, normal agriculture fields. To begin with, our site looks little different to any other pasture on degraded peatland. Over a period of six months, we have converted it to a new type of farm, a vision of what the future could look like. This "Paludi" farm will grow moss, a new crop with a range of applications, from providing seed material for nature restorations, to replacing peat in garden growing media. 

For more information about Moss as a product, please see our Paludiculture information page. 

 

Water water, everywhere….

When restoring a peatland area for nature, the aim is to keep the water in, and to support the establishment of a natural mix of plants. However we are aiming for a harvestable crop, and to grow as much of it as possible. Therefore we need quite a different setup.

The first challenge is water. Sphagnum is a wetland plant, and grows best when the water level is a few centimetres below the surface. However in our field, the damaged hydrology means that the water level can be well over a metre below the surface in mid-summer, especially in the recent very dry summers experienced in Northern Germany. Supply of water is a key consideration for any paludiculture site, so we have constructed a 2,500m3 water reservoir to ensure a steady supply for our sphagnum moss. Not to mention all that necessary tubes, and the measuring and control equipment.

We don’t like hills

The next challenge is the need for a level surface. If the water level is to be consistently 5cm below the surface across the entire growing area, the ground needs to be perfectly flat. The top surface has also been degraded through drainage. We need a good growing surface, so this necessitates the removal of a large volume of topsoil to create usable growing conditions

3 excavators and a tipper truck removing topsoil to create a level surface3 excavators and a tipper truck removing topsoil to create a flat surface.

Earthworks on our farm last winter

This is always an uncomfortable trade off in rewetting projects, and forms a complex dynamic around the carbon savings. The removed topsoil will release CO2 as it oxidises, so the objective is to ensure that the overall carbon balance is negative. Our calculations are presented at the end of the page. 

Once the level surface is created, irrigation trenches have to be dug to ensure an even spread of water. Although peat is a very effective store of water, it doesn’t spread water very well. To ensure that all parts of the soil are wet enough, 30cm irrigation ditches have been cut through the surface, with 6m wide growing areas between each ditch.

A frosty morning showing the completed surface

The nearly completed earthworks, one frosty morning

A mossy business

Finally, we need some moss. Like any crop, this needs to be sown, rather than letting nature take its course. Fortunately sphagnum regenerates after being spread onto a suitably wet ground, so doesn’t need to be grown from seed. This is an option that is available, with nursery plugs being sold to restoration sites. However, for this site we have used donor material, harvested from various sites.

A yellow long arm excavator harvesting moss from a field.

Harvesting Moss from a donor site

This was harvested by hand and machine from several sites, in order to ensure we had enough material to fill our hectare of growing.

And here you are,

That is how you build a farm. Easy, isn’t it?

A group of people spreading moss on the site.

Moss Spreading 

How much carbon are we saving? 

2,363 tonnes

This is not just about finding a new use for a site that was degraded, and acting as a buffer for the nearby nature reserve. We are also seeking to reduce the Greenhouse Gas Emissions from the site. 

Our initial estimate is that the degraded grassland was emitting 267 tonnes of CO2e* per year, a total of 31 tonnes per hectare. This means each hectare was emitting as much CO2e as 3 typical residents of Germany. 

Although we have used a lot of heavy equipment, the fuel is is a surprisingly small part of the equation, with only 15 tonnes of CO2e released, equivalent to half a hectare of drained peatland in one year. 

The major CO2e 'cost' of our project is the removal of soil to create the growing surface, which results in the production of 1,523 tonnes of CO2e. This is a lot of GHG, however one way or another given the degredation that had already taken place this was very likely to end up in the atmosphere anyway. 

That's the bad news out of the way, the good news is that the rewetting of the site immediately halves the CO2 emissions, saving 15 tonnes per hectare, and reducing the emissions by 132 tonnes per year. We can't eliminate emissions through rewetting, as wet peatlands release methane, a GHG with a potent 100 years warming potential. 

Over 30 years, this adds up to just under 4,000 tonnes of CO2. This gives us the net balance of 2,363 tonnes CO2e. 

 A graph showing the net saving against the CO2e costs

What we have not counted in these figures is the benefit of creating a sustainable replacement for peat substrates. Peat, when dried and used in gardens as a growing media, produces 200kg of CO2 per cubic metre. The potential CO2 savings of deploying this crop in place of peat in growing media would far outwiegh the net savings presented here. 

*CO2e - this stands for "Carbon Dioxide Equivalent." Ecosystems involve a complex exchange of gases, including CO2, CH4 (methane) and N2O (Nitrous Oxide), all of which contribute to Global Warming and are collectively known as Greenhouse Gases.