Thursday, 29 March 2018 11:00

Avoiding invasive tree roots

Written by  Dr Richard Smart, Smart Viticulture, Penzance, Cornwall, and Larry McKenna, Escarpment Vineyards, Martinborough

There is a simple solution to beating outside vegatation's compeition with vines.

Many vineyards have competition from outside vegetation. This is commonly from native trees or hedges, and sometimes natural wind breaks within the vineyard. While windbreaks have a powerful benefit in windy zones, they can also negatively impact vine growth by competition.

Competition may be for light, but most commonly for water and nutrients. This is especially significant in Australia, where the reach of Eucalyptus roots into a vineyard is amazing, and devigourating effects on vines can be seen for tens of metres. Root competition is also evident where windbreaks are planted in vineyards due to proximity to vines.

A simple solution

While consulting with Larry McKenna and the Escarpment team there was discussion of root invasion from a nearby shelter belt of Macrocarpa trees, some 10m high and 7m from the vineyard edge.

I rolled out to Larry my standard answer, and one I have used many time in Australia especially. Go hire a “ditch witch” for a day, and dig a narrow trench, 10 cm or so wide, and as deep as you can preferably to an impermeable sub soil. This ditch should be near the edge of the vineyard, leaving a reasonable root volume for the tree so as not to reduce its water supply. The trench will obviously cut the roots growing into the vineyard.

To prevent the roots growing back we use a double thickness of plastic sheeting, called “builders plastic” in some hardware stores. It is around 150 to 250 microns thick, and quite strong. It can often be purchased as a 2m wide sheet folded down the middle on a roll. 

Push the fold to the bottom of the trench and hold it in place with soil or stones. Lay out the plastic along the length of the trench. You can cut off surplus plastic to the ground surface. And you can put more soil in the trench, to hold up the plastic. That is it, root barrier completed.

Depending on the time of the year you install the barrier determines when you may see results. Often there can be an immediate growth response in the vines, especially in spring and early summer as the competition is removed. Hopefully you do not see retardation in the offending trees, especially if they are shelter belts.

Larry McKenna took the photo below on 30 November, at the end of a record dry spring. This remarkable photo shows the position of the trench and buried plastic, and the withered grass showing the effect of strong moisture competition from the trees on the right. The trench was installed 18 months ago, and shows that the plastic has prevented regrowth into the vineyard. 

 

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