I know that the first thing that crosses your mind when you twist out the cork of that last precious bottle of Pommard 1er Cru smuggled home in the half case in your carry-on luggage after your anniversary trip to France back in the days before the paranoia of the twittering fear mongers (nothing to fear but...) rendered corkscrews and even liquid itself verboten in-flight, before that rich, deep, very French odor of slate, raspberry and barnyard slips over the lip of the bottle, before your acknowledgement of the event you're celebrating, before your expectation of the table conversations that will be lubricated by maroon sunlight in bottle form, before the possibility slips through your consciousness of the extra-curricular activities (if you're lucky [sic!]) that might follow whatever event warrants such a fine bottle of magic...yes the first thing you will think of upon pulling that cork is, of course, the soil pH. Yes, you will wonder, yes, what exactly was the pH of the soil in which these grapes were grown?
Okay, maybe I'm making assumptions. In truth, unless the bottle belongs to a soil scientist, a vineyard manager, or someone with a serious problem, the last thing on your mind when you open a bottle of great wine will be the soil pH. After all, the acidity of the soil doesn't even relate, directly, to the pH in the finished wine. pH isn't a sexy wine word like "slate" or "shale" or "minerality," terms which have all become cliches among aficionados.
But soil pH is important if you're growing wine. The pH of the soil has an optimum range for vinifera, hybrids and native American varieties. Natives tolerate, and even prefer, the slightly higher acids of a low pH soil (remember, it's an inverse relationship, low pH = high acid). Cabernet franc, which I'm planting, prefers a pH of around 6.5. At this optimum range, soil nutrients are more accessible and are taken in at the right levels. While a low acid soil won't necessarily mean you wind up with a low acid wine, it can affect the overall health of the vine and thus the ripening and health of the fruit.
My soil tests showed that the pH of my first vineyard block at the new site was 5.5. Since I'm planting cab franc, I wanted to raise that pH to around 6.5. The way to do this, effectively lowering the soil acidity, is to add agricultural lime. It's a common necessity in our region. Your handy Extension person and or website can help you figure out exactly how much lime to add to your site to raise your soil pH.
Lime additions are calculated and measured and bought in tons. Even though I spent time growing up on a farm as a kid, I also lived in an apartment in Chicago for many years, so the idea of tons of anything is a foreign concept. I was sure it was going to be expensive to add appx. 800 lbs of ENM (effective neutralizing material, aka lime) to my one-acre bloc. Especially when a single 50-lb bag of pelleted lime cost six bucks.
There are two basic types of limestone...calcitic and dolomite. I have high magnesium content (call it 'mag' content to sound like you know what you're talking about) in my soil, so I wanted to add calcitic limestone as dolomite contains higher levels of magnesium. You can have too much of a good thing, and excessive levels of any nutrient can cause toxicity that is as dangerous, or even more dangerous, to your vines than not having enough nutrients. At first I planned on using bags of pellet lime, spreading them with a rented lawn spreader and a borrowed ATV. I thought this was a pretty clever solution, and when I figured out that it would cost me around 400 dollars to perform the entire operation, I was fairly satisfied. The problem was matching up the ENM rating of the limestone in question. ENM is measured in lbs per ton, so if you have limestone with a rating of 400 (per ton), and your experts tell you that you need to add 800 lbs of ENM, that means you need to add TWO tons of the material to reach your target. That's 4,000 lbs! A lot of stuff.
Once I figured this out, I grew scared...my cost was doubling, not to mention the workload. But then I learned you could buy lime by the 12-ton truckload. And what's more, a good agricultural co-op will deliver and spread it for you. The problem is that you need to buy a minimum of 12 tons. I thought this might cost a fortune, but then I learned I could get 12 tons for a couple hundred bucks...a fraction of the cost per ton than what I'd been planning to spend on bag lime. The only issue is that you have to have a place for them to spread the extra lime. I had them dump two tons on my one-acre spot (at 400 ENM per ton, that would mean I added the required 800 ENM to the bloc) and then spread the rest randomly around our property. That way I'll be ahead of the game when we plant new blocs in the future.
I had the field disked ahead of time to allow the lime to work down into the soil. I had to wait a few weeks for them to come out to our property as, believe it or not, 12 tons is not a very large project. They were liming area corn and bean farms with hundreds of tons, so they had to work me in. I met them at the vineyard, showed them where I needed the lime and they took care of the rest. I'll let it rain, then rip and then drag the bloc smooth in the spring to further spread the lime. I'll test again every year to to see how the lime levels are shaping up. A couple years down the road I can make adjustments as needed.
This is probably confusing to novices. It was very confusing to me, but now that I've gone through the process I have a pretty good handle on the hows and whys of spreading lime. I also understand concepts like acid rain better. This is a problem in the northeast...acid rain can reduce pH of soils into the low 4-range (increasing acidity). That would be no good for wine grapes of any variety.
So now at Thanksgiving or on your birthday or whenever you pop open that next great bottle of wine, maybe the soil pH will be the first thing you think about. I know I'll be thinking about it for a long time.