Miscanthus – For commercial mulch

8 April 2019

People use mulch for a variety of reasons but the two main ones are weed control and moisture conservation. As a result there are quite a few different types of mulching product that can be used. But for any material that is going to be used for mulch there are really three questions. How well does it conserve moisture? How well does it reduce or even eliminate weeds? How long does it stay effective?

There are of course other questions such as ease of laying, quantities required, cost and compatibility with the plants that are being mulched. All of these are important but the three primary questions need to be answered positively for the mulch to really have any chance of being a commercial success.

Materials that are currently used for mulch include barley straw, pine bark, sawdust and even wood shavings. There will be others but those are certainly the key ones in NZ.

Professor Wratten of Lincoln University did a trial in a feijoa orchard to assess the effectiveness of Miscanthus mulch when compared with bark, with or without the beneficial fungus Trichoderma. He looked at several characteristics of the soil and the crop, evaluating the effect that the mulches had on those characteristics. The Miscanthus mulch had, by a factor of at least two, the largest number of earthworms, together with the lowest soil compaction, significantly higher soil moisture and very importantly, the greatest picked fruit weight.

Interestingly, that orchardist commented some time later to Miscanthus New Zealand Limited (MNZ) that another unexpected benefit was that the Miscanthus mulch lasted considerably longer than any alternatives that he was familiar with. It was effective for at least two years from when it was laid, keeping weeds under control, maintaining soil moisture and no doubt keeping the earthworms happy. He is now very keen for his local garden centre to stock Miscanthus mulch - for both commercial use and home use.

A simple evaluation trial was done on a commercial strawberry block and this too was successful. When compared with the barley straw that is normally used, laying the Miscanthus was significantly easier. Additionally, the Miscanthus, being seedless, not only did not have any of its own seeds germinating - unlike barley straw - but also prevented weeds. So there was no need to spray for weed control at all. The durability of the Miscanthus mulch was something that was not evaluated there but is certain to have been evident when compared with the barley straw.

Miscanthus mulch has also been tried for home garden use by several people and all have been happy with the results. The only problem with supplying this market is the lack of a suitable bagging plant – for smaller bags. There is probably a need for a bagging plant for the commercial mulch use too - but with larger bags.

As a result of this research and also because of the ease of use of Miscanthus mulch - which can be laid mechanically in commercial operations - MNZ is of the opinion that there is significant potential for use of Miscanthus mulch for water conservation and weed control in commercial crops. This will include grapes, kiwifruit, avocados and other fruit trees. In addition, use of mulch in botanic gardens, parks and other local authority plantings would also seem to be logical.

Regions with drier climates such as Hawkes Bay, Nelson and Canterbury are obvious choices and they are all good places for growing Miscanthus providing there is adequate water supply. MNZ has seen barley straw mulch being used in Hawkes Bay on an organic orchard, but this was done only in the first two or three years, primarily just for weed control. It is costly to lay it - unlike Miscanthus. After those first years, mechanical scarification of the soil is used in those orchards for weed control. One would expect that to cause soil moisture loss. So there seem to be enormous opportunities for Miscanthus to be used for water conservation while also carrying out weed control. The fact that Miscanthus mulch can easily be certified to be organic is an additional benefit.

Alain JeanRoy of France Miscanthus is on record as saying that the 1/3 of their Miscanthus production that is not used for energy, is divided between mulch and animal bedding. The focus at the time he said that was really on mulch and he pointed out the use of Miscanthus in flower crops for weed control.

NZ needs a greater number of hectares of Miscanthus planted right now. This is beginning to happen with a small number of progressive, innovative customers, but in order to supply the demand that is already in existence, MNZ would be very happy to plant a few hundred hectares of its own right now. Unfortunately lack of adequate available funding means that MNZ is currently unable to do so. If MNZ was able to do that, it would then make a lot of sense to also set up a Miscanthus mulch bagging plant. Then commercial users of mulch - be they local authorities, orchardists, strawberry growers or even those producing flowers, could have ready access to a long-lasting, very clean, weed free mulch that will enhance their whole operation while at the same time improving their soil health and reducing the water demands of their crops.

ENDS

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