When to Begin Fertilizing in Spring?
It’s likely not a good impulse to want to lasso students to slow down their spring fertilizing, but I admit to the urge. And yet I get it: the trees are growing, so we reach for the fertilizer by instinct.
The problem with this is that by the end of summer everything, even old geriatric bonsai, look like young goats in a pasture, jumping around everywhere. We need a bit more selectivity.
Illustration by Sergio Cuan for one of the fertilizing chapters in my recent book Bonsai Heresy: 56 Myths Exposed Using Science and Tradition
Some plants really do need fertilizer right out of the gates. If you plan on decandling black pines, just before they begin visibly growing is the prime start time. Chojubai could use some early in the growing season as well. But those are rare; for the most part, for developed bonsai, let them grow a beat of time before fertilizing. Maybe wait a month or two.
We have, though, many undeveloped, younger bonsai. Many of those can benefit from some fertilizer in spring as they begin growing. This translates into greater caliper, more buds, faster build. Very old collected trees don’t need lots of fertilizer; for these a mild push is all they need, later in the spring.
I’d encourage the use of a slow release of some sort. Organic fertilizer balls or cakes are excellent (or perhaps small amounts of osmocote or apex, synthetic slow release fertilizers). Liquids work, but are labor intensive to get the right dose to the right plant. Another advantage to solids: if you get frequent rains in the spring and fall, with wet soil for weeks, the bonsai still get fertilized. If the pot is sopping wet you’re less likely to want to water in fertilizer.