Experimenting
with growing mediums
a study by the University of Ghent
Ce texte sera très prochainement lisible en français.
1. INTRODUCTION
During recent years, the cut-flower sector has had its share of the problems. Intensive monoculture has exhausted the soil and made it more prone to host desease. Especially gerbera's and roses suffered from these problems and such plants are consequently grown on artificial substrates. Rockwool has had its share of success but its major disadvantage is that it creates a huge mount of waste. Research is done all over the world to find ways to re-use the rockwool beddings and experiments are carried out to investigate the possibilities of natural growing mediums, such as coconut husks.
Our Research Centre has set up a whole programme of experiments in order to define the possibilities of growing mediums and, in addition, to determine the ideal dosage of the watersupply for each of them.
For the time being, experiments with three different growing mediums are under way.
• A comparative study of reconditioned and new rockwool versus two substrates based on coconut-husks in order to determine the influence of the growing substrate on the quality of the flowerstems of two mini-gerbera varieties: 'Lily' and 'Kaliki'.
• A comparative study of several coconut substrates (peat, chips, fibre neth medium) for growing 'Golden Gate', a hybrid rose.
• An evaluation of the use of coconut chips or a mixture of coconut fibres with soil as far as the productivity of Alstroemeria 'Pink Minetti' and 'Little Sun' are concerned, in comparison with plants grown in the soil.
2. THE SUBSTRATES
The tests are carried out with two main groups of substrates: rockwool and coconut derivates.
2.1 Rockwool
Rockwool is a mineral growing medium which is being produced by melting a volcanic mineral at 1,600°C and injecting the liquid lava between two disks, rotating in opposite directions. In that way, the lave is being stretched into thin fibres. Because the soil became exhausted, the first tests had been carried out on rockwool already in the middle of the seventies.
At that time, rockwool seemed an ideal growing medium because it allowed to avoid expensive chemical desinfection measures of the soil when growing head-lettuce, tomatoes, cumcumbers and the like. When it showed that productivity could be stepped up in the same process, the use of rockwool rapidly extended to growing non-edible produce such as Gerbera's and roses.
Since the public has become increasingly aware of ecological problems in general, the enormous heap of waste generated after each growing season remains a considerable drawback. So, growers are always on the look-out for new ways to desinfect and re-use old rockwool beddings.
3. PHYSICAL PROPERTIES
4. RESULTS OF THE CURRENT TESTS
2.2 Coconut substrates
Pure coconut growing mediums may be classified in three groups. Coconut peat, coconut fibres and coconut chips. Traditionally coconut peat is the more frequently used medium. Peat is a by-product of the production of fibres. The peat can absorb huge quantities of water but leaves relatively little room for air. Coconut fibres on the contrary, absorb very little water but provide lots of airspace. These properties make coconut fibres less adequate as a growing medium. It can however successfully be used for soil-improvement. Coconut chips are being made by chopping the husk, the outer skin of the coconut. The chips come in three sizes: medium, small and fine. The husk is very hard and porous at the same time. Tiny airducts allow the nut to breath and grow inside the husk.
Fibre neth medium is a rooting substrate. It is a mixture of short ends of microscopically tiny fibres and coconut peat which, after steaming, forms a spongy substrate that is held together by an invisible network of fibres.
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