Mouton Noir

One of topics in viticulture that took me way longer to understand than I care to admit is the bud development in vines. And the very problem getting in my way of understanding was, of course, myself.¹ I simply could not fathom, even at a conceptual level, that a plant could plan its reproduction in a multi-year cycle. But vines very well can and they do.

Here's the ELI5 notes to myself.

Imagine a grapevine is like a tiny factory that takes two years to make grapes, and it keeps repeating this process every year.

First Summer – Starting the Journey: The grapevine begins by preparing tiny buds in the axils, where the leaf stem attaches to the main stem. Inside these buds are parts called SAMs (shoot apical meristems), like little artists who can create leaves, flowers, or tendrils (the curly parts that help the vine climb).

Early Spring – Waking Up: When spring comes the next year, the vine wakes up these tiny buds. They start growing out from where they were formed, in the axils.

Late Spring – Making Choices: By late spring, the SAMs in these buds have to decide whether to keep making leaves and tendrils or start working on flowers. This decision depends on how much light the buds get in their axil locations.

Gibberellins – The Decision Makers: Gibberellins, acting like messengers, tell the SAMs what to create. In shady places, gibberellins encourage the vine to grow longer and make more tendrils instead of flowers.

The Next Spring – Final Steps: In the second spring, the buds, still in the axils, are ready to turn into flowers or tendrils.

Flowering Time – Creating Grapes: If the weather is warm and nice, these flowers (in the axils) can pollinate themselves (since they have both male and female parts), and that's how grapes are made.

Cycle Continues – New Buds Form: After the grapes, the vine starts preparing new buds in the axils again, beginning the whole process over for the next year.

This whole process takes two years for one cycle of grape production, and then it starts all over again for the next cycle. The vine prepares for flowers in one summer, but the actual flowers only show up in the spring of the next year, and then new buds begin forming for the next cycle.

Note(s):

1: I simply assumed without even questioning myself that all cycles in nature have cycle lengths of at most one year. I just could not believe an organism could incorporate two years of uncertainty into its reproduction cycle.² 2: It all began to make sense when I realised grape vines are perennial plants and would always be growing and venturing out to all kinds of directions in the wild. The image of grape vine that I had, the one of Guyot or Cordon trained vine at vineyards, is, in fact, unnatural!