More bark than peat

Press, 20 April 1982, Page 24

More bark than peat

Bark is being widely used in New Zealand as a substitute for the traditional growing medium, peat.

Research into the use of bark in horticulture has been carried out by scientists at the Levin Horticultural Research Centre, according to the Ministry of Agriculture and Fisheries.

Bark has many advantages over peat — it is easy to obtain, relatively cheap to produce and it is sterile, which makes it suitable for use in the export of plants.

The chief M.A.F. researcher in the project is Dr Munoo Prasad, scientific officer in charge at the research centre’s soil and plant analysis laboratory. The limited availibility of peat and the large costs involved in transporting it prompted Dr Prasad to investigate the use of bark in 1977.

Useful tannins and polyphenolic compounds can be extracted from the bark and used as adhesives in plywoods and other processes, leaving the medium sterile.

According to Dr Prasad, the bark, when mixed with fertiliser, performs just as well as peat. The fact that the bark was easily available

from sawmills throughou the country and because it was sterile means that the discovery was a major breakthrough for horticulture.

The ground bark for horti culture is already being pro duced and made into potting mix in several parts of New Zealand, and at least one firm is known to be looking at exporting it to Hong Kong and Singapore.

It is important that the correct fertilisers be added to the mix because it tends to retain nitrogen and phosphorus. Both fertilisers can be added with the slow release fertiliser usually added to potting mixes. Particle size is important in the use. of the bark medium because this, governs the amount of water and air available to the plants. Different grades of granulated bark have been found suitable for different purposes, ranging in size from o.smm to 2.5 mm. Combinations of these sizes have been found suitable for potting to mulching.

Both ornamentals and food crops seem to grow well in the bark. Research has shown no difference between plants grown in bark compared with those grown in peat.