Night Time Temperatures

I have been thinking about the issue of night time temperatures as it relates to growing grapes. Living in Maryland, it has often been stated that the warm nights will result in lower acid grapes and that cooler night time temperatures are required to retain acidity. Yet I have seen pictures of vineyards in Spain and southern Rhone where the vines seem to come out of a sea of rocks. It is often noted that these vineyards are good because the rocks absorb the heat of the sun and keep the vineyards warmer at night. This seems to contradict the need for cooler night time temperatures. Am I mising something here?

Hi Brain,
You’re absolutely correct, cool nights do produce grapes with more acidity. The metabolism of the vine actually slows down somewhat on cooler nights and they don’t require that much energy. Whereas on warmer nights the vines’ metabolism doesn’t slow down as much and it does convert some malic acid into needed energy. As far as the Rhone goes you can not forget about the cold winds that funnel down the valley from the northern highlands and the late spring and early fall fogs that could settle just above the vines thereby cooling the vines down. Always remember it is micro-climate (and everything else that goes with it) that counts.

Salute

O.K. so the night temps in S. Rhone and other places may be cooler than I thought. But still not sure I understand why the heat from the rocks is considered a good thing. Anyplace that has enough heat to ripen Grenance and Mourvedre properly is going to be plenty hot enough. Some of these vineyards appear to be with low trained or even bush trained vines such that the impact of the rocks would be greater. I am not sure how much difference this makes overall. Still it seems to me that either the rocks do little to nothing as it relates to overall vineyard temperature profile and it is just a nice story. Or there is a positive impact in which case that leads one to believe the either there is a limit to how cold one wants the night time temperatures which is what I think your essentially stated. Only thing I could think of that maybe gives both a benefit to the rocks and still agrees with the cool night temperatures is that the rocks slow the rate of change from the daytime highs to the night time lows and this may be a postive.

Yes the Southern Rhone is well known for its galet, the rounded, heat absorbing stones and in some of the area vineyards these stones may be found everywhere. But one must look beneath the stones and basically the soil underneath is much more varied than one thinks. In some of the area vineyards the soil is composed of a high proportion of clay. Low bush training makes sense, for a two or three wire trellis system would be devastated by the howling winds.

Salute