Glacial Soil & Wine Quality

And why the interior of BC has such fascinating terroir.

With a degree of frequency I hear from farm and wine people that our soil isn’t that interesting. It seems less romantic than the chalk of Champagne or terra rossa of Coonawarra.

This is a mistake – we have fascinating soils with a high degree of variability and quality potential. And there’s a reason to understand them for the massive impact it has on growing and winemaking.

The image above is of the same area in a vineyard. The top picture is two of the soil classes we identified (labelled as F and G) and the bottom is a terroir mapping we did. Dark blue is low water availability/sandier texture, hot pink is the opposite with more clay and/or water available.

When we dug the pits in this area we saw a drastic difference in the nature of the soil and thus its affect on the plant.

Soil class G is glaciolacustrine in origin, is well sorted with very clear stratification and a (relatively) high clay content. We see very few stones due to how the soil was formed from lake bottom. It’s upper layers are made of loam with a high capacity down to at least 1.5m to hold water, while still being well draining.

This would be a soil that has the possibility of limiting the quality of bigger reds and would be more well suited for whites. If reds were planted here, it would be important to appropriately time stress and watch over-watering.

By contrast, soil class F is glacial till. Glacial till is the result of direct glacial deposition (in contrast to glacial lake bottom or glacial meltwater) resulting in an unstratified (ie. all mixed up) soil with a high number of “rocks”. This means a high degree of sharp-edged cobbles which obviously have no capacity to hold water or provide plant nutrition. Although the soil is sandy loam down to at least 1.4m, which should have adequate water holding capacity, the high percentage of cobbles result in a very low capacity to hold onto water. This means irrigation frequency needs to be increased due to the soil’s complete inability to hold water in roughly 40% of it’s mass.

For this reason, although the soil has many challenges, it’s well suited to larger reds. The natural stress induced by unavoidable water restrictions, and the impact this has on root exploration, will improve all the characteristics that are desirous in red wines. You will naturally see lower yields and smaller berries, as well as increased phenols, tannins, and other chemical attributes that improve red wine quality.

One of the exciting, and challenging, facts of growing grapes on soil of a glacial origin is all of the variability it introduces. You can have a pure silt loam two meters away from a 97% sand zone.

But this also brings the potential for something unique and exciting. There are not many winegrowing regions in the world growing on this type of glacial soil – especially once you factor in how calcareous the soil is.

It means we need to work harder than most to understand it – there’s no classifying wine quality by height on the slope. And it means that we have to be more targeted in our management to bring out the best of our terroir.

And that should be exciting!