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Saturday, January 7, 2017

Using Rock Instead of Wood for Mulch Around Grapes

Q. I am putting in 30 more wine grape vines. I was thinking of using chat, crushed rock, for mulch rather than wood chips. What do you think?

A. The idea of using rock mulch, rather than wood chips, addresses a controversy among wine grape growers. Some growers of high quality wine grapes believe that wine grapes must “struggle” to produce a good quality wine grape. They believe the best wine grapes come from poor soils and a limited water supply.
Jerry Nelson with John Arellano from Duarte Nursery in California

Wine grapes without any kind of mulch growing in raw desert soil near Amargosa Valley, Nevada. Jerry Nelson's vineyard.

The hot desert, with nighttime temperatures around 90° F or more during harvest time, is thought to produce a poor quality wine grape. It is believed that nighttime temperatures should be cooler than this during harvest.

Grape harvesting event I put together for Slow Food Las Vegas at the Gehring Vineyard in Amargosa Valley, Nevada.
Few people believe that a good quality wine grape can come from this type of environment. This may not be true about table grapes. Some of these same producers believe that soils for wine grapes should not be full of nutrients. Adding compost or soil amendments that improve the soil, they believe, produces a grape without intense flavor typical to the variety; a poorer quality grape. I might point out that the flavor attributes of wine grapes is valued much higher than table grapes.

Roger Gehring and I at his orchard in Amargosa Valley, Nevada, several years ago when his vineyard was first established.
The verdict is still out but I believe that wine grapes struggle enough in our climate and soils without additional stress from poor soils and a lack of water. I have seen wine grapes grown in backyards in our climate without soil amendments. The soils around the home, in these cases, was “fill dirt” specified by the contractor. These did, generally, poorly. I have seen wine grapes grown in our climate in native soil, with no organic surface mulch such as wood chips. These did much better. I might point out that in cases like these the soil was a good agricultural desert soil, not “fill dirt”.

Wine grapes at the UNCE MG Orchard in North Las Vegas, Nevada showing 3 to 4 inches of wood chip surface mulch.
I have concerns about growing wine grapes in home landscapes if the home was surrounded with fill dirt. I believe this soil should be amended at the time of planting and the soil surface should be covered with an organic mulch, such as wood chips. I am concerned that applying rock mulch, like chat, to its surface will lead to future problems for wine grapes and many other landscape plants sensitive to poor soils and not intended for our climate.

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