The leaf growth of a fruit tree in spring is as fast and dramatic a change as any in the world of plants. As cherry grower Mike Omeg says in an AEA webinar, “In the spring, cherries go from having very small leaves to having a fully expanded spur leaf in just four or five days”

But most of the energy that generates that leaf doesn’t come from the roots, as you might think–it’s actually stored primarily in the buds. In fact, there’s very little sap flow from the tree’s roots into the upper part of the canopy until after bloom.

The first leaves that emerge–the spur leaves–are the critical driver of fruit growth: as much as 80% of the fruit’s sugar is sourced from its closely associated spur leaves. The highest-yielding crops that John Kempf has observed had “individual leaves [that] were very large in size, which resulted in an abundant sugar source for the fruit.” The size and quality of those spur leaves is determined by nutrition stored over winter by the buds.

What this means is that all of a tree’s flowers and all of its most important leaves are built from energy reserves that the tree accumulated the previous season. 

This is easily demonstrated by “forcing”—you can cut a branch from a fruit tree in early spring when the buds start to swell. If you bring it inside and put it into water, it will go into full bloom. Every mineral that goes into making those flowers—and that produces their color, fragrance, and pollen—was present in that stick, primarily in the buds. 

“That just shows you the amount of nutrition that’s stored in those buds themselves,” says Omeg.  

How can a fruit grower use this feature of trees to their advantage? 

The key is to make sure the buds are packed with as much nutrition as possible, so they create the most abundant, healthy flowers. And since buds are formed the previous year, you have to make sure the tree has abundant nutrients after harvest, when it actually builds those buds. All those nutrients will be directly responsible for the quality of blooms, and therefore the quality of the coming crop.