One of the challenges of having a vineyard that is approaching middle age is the accumulated toll of vine loss. In our oldest blocks, which are approaching 30 years old, the combined impacts of gophers, trunk diseases, virus, and our stressful environment means that we've lost between 10% and 40% of the vines. And it doesn't take anything catastrophic to get to those numbers. Imagine a 2% vine mortality (one in every 50 vines) per year. After 10 years, you've lost 18% of your vines. After 20 years, you've lost 33%. And after 30 years, you've lost 45%. That's just math.
Replanting missing vines among those that have survived is usually an unsatisfactory response to this vine loss, for a couple of reasons. The roots of the vines that survive tend to encroach into the space of any missing vines, which makes it difficult to get the new vine established. And because we're trying to dry-farm our mature blocks, getting the new vines the water that they need to get established tends to work at cross-purposes to the vine training that we're doing, encouraging surface root growth from established vines, which is a waste of their resources.
The difficulty in getting new vines established among the older vines has meant that we've lived with lower and lower vine density in our older blocks. That comes through in lower yields. Looking at the yield per acre the last few years on these varieties compared to our average in the 2000's shows the cumulative impact. Last decade, Mourvedre averaged 2.8 tons/acre. Over the last five years it's averaged 2.2. Counoise in the 2000's also averaged 2.8 tons/acre but has declined in recent years to 2.5. Syrah has declined from 3.4 tons/acre to 2.6. And even Grenache, typically the most vigorous and productive, has seen average yields decline from 4.3 tons/acre last decade to 3.9 over the last five years.
Because of the challenge of establishing new vines among the old, we're left with the difficult choice of when to pull the plug and pull out an entire block to start fresh. If the surviving vines are struggling, or the blocks were planted to the wrong variety or on the wrong rootstock, it's worth the sacrifice to pull them out and replant. We're in that process in a few blocks. Each has its own story.
- One was originally a Viognier block that we planted in an area that turned out to be one of our frostiest. By the time that we realized that and grafted the block over to the late-budding Mourvedre, even the vines that survived were weakened by the years of frost damage.
- Another was a block that had originally been planted in 1992 to California-sourced Mourvedre (Mataro) clones. We decided in 2003 because of dissatisfaction with the ripening of these clones to graft the block over to our French Mourvedre clones, but that didn't fix the issue. It might have been a rootstock incompatibility issue, or a virus problem. In the end, we decided to start fresh.
- Finally, the third block that we pulled out included Syrah that we made the mistake of pruning during wet weather one year back in the 1990s, and we've been struggling with fungal trunk diseases ever since. We lost some vines, but even the ones that survived were weakened. Again, it seemed to make sense to start from scratch.
But what to do about a block that's missing 40% of the vines, but still making some of our favorite wines? We're trying out a new technique to build vine density in a couple of these blocks. It's called layering. Really, it's an old technique, and takes advantage of the fact that grapevines have the ability to reproduce asexually. If you bury a grapevine cane, each bud has the ability to sprout roots. The connection to the parent vine helps nourish the new vine while those roots get established. Eventually, you can cut the connecting cane and the new vine will grow on its own. Wikipedia has a simple diagram of the process (right).
A few pictures of how we're doing this at Tablas Creek will help illustrate. First a photo of the block where we're trying this: an old Syrah block, planted in 1992 and 1994. You can see that we're missing a lot of vines, probably close to 40% overall:
What we've done is to extend an extra cane, beyond what we're using for the vine to produce fruit that year, from a healthy vine, and then bury it underground and bring it back up in the position of a missing vine:
Those vines are now sprouting:
Those new vines will grow, supported by the established root systems of their parent vines, for another couple of years. At that point we can choose to cut the connecting cane or leave it. This can in theory be done infinitely: one vine being layered into another, into another, and another. We've heard stories about entire acres being propagated in this way from a single starting vine. We don't plan on anything so extreme, but if we can rebuild the vine density in some of our favorite old blocks without having to pull out our old vines, that's a huge win for us. We'll be looking at the success of this effort in this Syrah block, and if it works, applying it to other blocks that might benefit. Stay tuned!