Mussel shell mulch trialled on grapes
The Marlborough Express
Relevant offers
Previously dumped mussel shells could find a new use under Marlborough's vineyards, if a trial using them as mulch takes off.
Jim Greer, who grows grapes near Renwick, is trialling mussel shell mulch on a small part of his vineyard.
As well as helping retain moisture, the shells reflect light up into the canopy to improve the development of red grapes. As the shells lay out in the elements they would become whiter and whiter, increasing their reflective qualities.
Mr Greer laid the shells down over winter so it was too early to say if it had been effective on his grapes, although he believed he could see a slight improvement already.
"But I think it's just great mulch. Even if it doesn't do much good, it saves on weed spray," he said.
"Years ago we laid a driveway with mussel shells, and when we took a soil sample after a couple of years everything was pretty good there, with stuff like calcium. And I always wanted to try it on the vineyards."
There were no problems with smell or salt as the shells had been processed and left for about six months outside.
Mr Greer could be on to a good thing, as mussel shell mulch has been trialled since 2003 at Nelson's Neudorf Vineyards.
Co-owner Tim Finn said the light reflected off the shells certainly ripened up the flavours while not necessarily ripening the sugars.
Mr Finn said he was putting more shells down this year on the grape varieties that were harder to get past the "green stage".
And senior lecturer in viticulture at Lincoln University Glen Creasy, who was in charge of the trial, said the mulch was an "exciting" project.
That Neudorf Vineyard was now doing it commercially and grapes from the trial were going into the winery's top pinot noirs, an endorsement of the shells, he said.
Dr Creasy said he was confident that each year of the trial was showing significant differences in the grapes.
The differences were difficult to quantify, but were definitely detectable on the palate, he said.
He said they showed "more ripe fruit characteristics" and a greater amount of suppleness on the palate.
Dr Creasy said that mussel shell mulches might not be ideal for all vineyards, but could help with the "more recalcitrant" blocks which were difficult to grow on.
He said the original idea was to change the flavour of the berries without changing the sugar content, because too much sugar meant too much alcohol, which would put varieties such as pinot noir out of balance.
It was a longer term question as to whether nutrients would leach down into the soil, he said.
The mussel shells appeared also to interlock, which meant weeds found it more difficult to grow through, and Neudorf was spraying one or two less sprays each year.
"I am really pleased with the way the trial has gone. The fact that its a waste product and finding another use is fantastic."
