Peat remains indispensable in potting soil for now

Less peat and more alternative raw materials in potting soil. While one grower is gaining experimental experience with peat alternatives, the other grower has sworn for years to a mixture that best suits the cultivation and range.

The extent to which gardeners with pot and container cultivation are involved in peat reduction and peat alternatives depends on the range and their sales channel. If they supply to retail chains of garden centers or hardware stores, they feel more demand for less peat.

Peat alternatives are not yet a problem in the sale of Boomkwekerij Menkhorst in Gelderse Gander. ‘We supply the Dutch trade and we export a little,’ says Anja Menkhorst. “No one has yet told us to use less peat or no peat at all.”

Mix

Menkhorst always uses a mixture of different raw materials because the company grows a large assortment of ornamental shrubs in pot sizes from P9 to containers of 7.5 and 18 litres. ‘Then you choose a golden mean in relation to potting soil.’ Her mixture consists of rice husks, bark, coconut fibers and peat products. ‘We are fans of rice chaff because it keeps the potting soil airy and ensures fewer weeds in the pot.’


‘Poke soil with peat is becoming more and more expensive, as are spreading agents such as bark’

The potting soil is unloaded at the potting machine by truck. ‘About 48 cubic meters at a time, preferably as full as possible, because transport is expensive’, says Menkhorst. ‘All raw materials for potting soil have become significantly more expensive in the past year.’

High buffer capacity

Planteskole Vredebest in Waddinxveen, South Holland, uses a mixture consisting entirely of peat products. ‘For us, the quality of the end product is the most important thing. We grow best in peat. Peat has a high buffering capacity for moisture and nutrients,’ explains director Hendrik Hak.

The company specializes in a range of conifers in various pot sizes. This finds its way through the intermediaries to, for example, foreign dealers.

Peat reduction and cattle-free

Hak certainly hears noises from the market about peat reduction and peat-free, but he has not yet felt compelled to go along. The problem keeps the grower busy. ‘If it is necessary and there are sufficient peat alternatives in stock, we would like to be able to switch.’

A few years ago, Hak gained a lot of experimental experience with peat alternatives. Even peat-free potting soil. The buffering capacity of moisture and nutrition was not always able to reach the peat level.

Sprinkle with bark

After potting, all Vredebest’s pots are sprinkled with bark as standard. As a result, the pots are not completely filled with peat products, but 80 per cent. The 20 percent bark actually already reduces the peat on the farm, although the spreading is mainly intended against moss and weed growth on the pot. ‘And we think it looks nice,’ says Hak.

Many growers sprinkle pots with bark as standard. They have to, because Mogeton – the only agent against moss and weeds in the pot – is no longer allowed.

‘It’s a real shame’, says Rajko de Hoon from Van der Peijl Tuinplanten in Zundert, Brabant. ‘That is why, but also because of its ornamental value, we sprinkle with bark. We try to make a weeding round every week and hand pick what is still growing through the bark. But it requires time and staff.’

Fertilization

Van der Peijl Tuinplanten uses different potting soil mixes, an acid-loving mix (pH 4.8) for growing azaleas and rhododendrons, a bush mix (pH 5.3) for potting in autumn and a bush mix for spring. “It only has to do with fertilization,” explains De Hoon. ‘We grow the plants that we pot up in autumn indoors. In the spring we pot up for outdoors.’

The potting soil consists partly of peat. A large part has already been replaced by wood fiber. “Peat is quite important for our crops,” says De Hoon. “Retailers sometimes ask if the company grows peat-free. Then we honestly state that we use less peat, but not peat-free. We can’t do that yet. The amount of peat alternatives would also not exist if everyone had to grow peat-free.’

Locally grown alternatives

Van der Peijl Tuinplanten is now testing locally grown peat alternatives such as Miscanthus giganteus (elephant grass) and tagetes (marigolds), which have been mixed together with compost in a potting soil with less peat. Until now, the test plants have had a growth inhibition compared to the standard mixture.

The ‘PH’ is too high and the marigolds started to sprout in the pot. We will definitely give the experiment a chance, because it will lead to less peat in the future. Good soil remains the basis for healthy plants,’ says De Hoon.

miscanthus

Planteskole Joost Sterke in Haaren, Brabant, is in full swing with miscanthus as a peat alternative. The company started testing as a cover material for pots five years ago. We liked it so much that pots and containers up to 15 liters in volume are sprinkled with miscanthus as standard. At 2 centimetres, the cover layer is as thick as the edge of the pan.

‘We therefore have fewer hours to weed’, says student Simon Peters, who does market research in miscanthus at the nursery from HAS Den Bosch.

Joost Sterke now grows miscanthus himself, not only to be able to use it as cover material, but also as a component of potting soil. ‘Poke soil with peat is becoming more and more expensive, but so are spreading agents such as bark,’ explains Peters. “Miscanthus is cheaper than peat.”

Simon Peters shows miscanthus, which Joost Sterke uses as cover material and as a component of potting soil. © Arno Engels

Cultivation and processing of miscanthus even for pot cultivation

In the tree plant sector, Plantenkwekerij Joost Sterke in Haaren, Brabant, is the first company to focus fully on Miscanthus giganteus, based on the idea that peat use in potting soil should be reduced. Sterke, who grows ornamental shrubs and hedge plants in the field and in pots, has 10 hectares of miscanthus and also supplies rhizomes to new miscanthus growers. ‘The crop grows by itself’, says Simon Peters from the company. “In the first year after construction, some weeds grow, but from the second or third year, the miscanthus grows so high that the ground remains free of weeds. You must never fertilize’. The rhizomes can remain in production for up to twenty years. Strong sheep harvest the crop in March with a corn chopper. In winter, it dries out completely so that the grower can process it. The grower does it himself. For this, Daar Agrotechniek has built a large screening installation, under which four big bags are suspended for four screening fractions of the fibres. The material can then be left in a pile outside. ‘The top layer of the heap gets wet because of rain,’ reports Peters. “But inside, the hope is pretty dry. The pile doesn’t get hot either and therefore won’t start composting. Ideal.’ The company uses the sieved miscanthus as cover material for pots and also supplies it to other growers. The larger the pot, the larger the sieve fraction can be. In addition, Sterke now mixes up to 15 percent miscanthus into its potting soil on a trial basis. ‘The plants grow well in it. We see little difference in potting soil without miscanthus.’

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