Wind Machines

Since I'm here in Ontario for a while, one does get to touring around vineyards (and wineries!) a bit.

In NZ, wind machines are popping up all over the viticultural landscape, as the most common type of frost occurring in the spring are radiation frosts. Something that moves the air can be very effective in avoiding freeze damage to the vines, because in such a frost cold air develops near the ground, but warmer air accumulates on top of that cold air. This is called an inversion layer, with the warm air stacked on top of the cold.

A wind machine sticks up far enough above the ground (say, 10m) to draw this warmer air down and mix it with the colder air. In most cases, there is a significant reservoir of heat in the inversion layer, meaning that the mixed air is warm enough to prevent freezing of the vine tissues for many hours.

Helicopters are also used to mix the cold and warm layers, but if a vineyard is in a location that is hit consistently with frosts, it can be worth the capital cost to buy, install, and maintain the fans.

So in NZ there are a lot of wind machines being put in to help manage spring freeze events, but here in the Niagara region, they are also putting them in. However, spring frosts are not so much of a concern here (due to the general climate and also the location of the vineyards). So why are people investing in these expensive machines?

Here the main problem is freezing temperatures during the dormant season. Grapes can be very hardy plants, surviving very low temperatures (for certain species, this can be down to less than -40 degrees C!), but vinifera vines tend to be more tender, with a critical temperature of around -18C. So if the temperature in a region tends to get lower than this on a regular basis, you had better have some methods to manage the vines to prevent damage!

One method relies on the presence of the inversion layer, which can appear in the middle of winter as well as in the early spring (or autumn). By mixing the air, freezing temperatures low enough to damage dormant vine tissues can be avoided, leading to productive vines the next season. Without some form of protection, crop losses can be 100 percent, with the added burden of having to re-train the vines (if you're lucky) or re-plant them (if you're not lucky!).

I will write on other strategies to avoid winter freeze damage in another post...