Fertilizing Your Bonsai

American bonsai enthusiasts tend to underfeed their trees. This is a remnant of an old school myth that was taught years ago. Less fertilizer=less growth, equals a tree that is easy to maintain, or keep small. The problem is that under fertilizing does not keep your tree small, it keeps it weak. We see yellow leaves and needles all the time, which is just too hard on your trees. You cannot do effective work on weak trees. They will never thrive, never look healthy.

This is where Michael Persiano’s “Superfeeding” regimen seems so outrageous to most American hobbyists. We are scared to death we are going to burn the roots of our trees. No one is suggesting pouring fertilizer straight from the bottle over your root ball. But if you feed with organic fertilizers and use a very free-draining inorganic soil, you will see phenomenal growth.

Of course, Persiano is correct when he says, “Verdant growth is the palette from which the bonsai artist works.” Perhaps not a perfect quote, but the idea is there. We cannot produce beautiful trees if they are not healthy, and we cannot keep them healthy if we do not feed.

How much to feed? If you have old issues of Bonsai Today or International Bonsai, look at the fertilizer cakes on the surface of the pots. Sometimes you will see a pot completely covered with cakes! So the question is; why are we so hesitant? It’s because we are unsure of ourselves.

Now do we just cover the pot with fertilizer cakes and forget about it? There are several reasons not to.

• Organic fertilizer cakes are only effective for about four weeks, so they need to be replaced in that time.
• There are specific times we want to remove all the fertilizer to achieve specific ends.
• It’s never a good idea to just try to automate our processes unless we really have a good grasp on the fundamentals.

There is a good rule of thumb about fertilizing your trees, which will come in handy if you do not have a schedule available. Some trees are best designed using the spring leaves or needles, and some are best using summer leaves or needles.

For instance, Japanese black pines and trident maples, even though one is a conifer and the other a deciduous tree, are fertilized in much the same way, because we remove the spring growth to make room for finer, more ramified summer growth.

Likewise, Japanese white pine and Japanese maple are fertilized in much the same way since we want to use the spring growth.

These trees will not push a second flush of growth like the ones mentioned above, so we treat them differently.

So the rule of thumb is, “Spring leaves or needles—fertilize in Fall. Summer leaves or needles—fertilize in Spring.”

Of course as all rules of thumb, this is very generalized, so here is a chart that is still general but tending toward the more specific.

It’s also important to note that mature bonsai are handled more subtly than young trees in training. This is designed for strong growth when and where you want it. It is by no means comprehensive.

Remember many things affect the way you fertilize. There are differences in method for:

Mature bonsai

Bonsai in training

Old trees

Young trees

Strong trees

Weak trees

And for your environment, whether you are hot and dry, at high elevation, heavy humidity, or whatever your microclimate might be.

Tree	Notes	Spring	Summer	Autumn	Winter
Conifer	4-6 weeks after repot
Black Pine		More	None after candling	Half	None or little
White pine		None until leaves harden	Moderate	More
Juniper	All year, moderate		Less in heat of summer
Deciduous
Trident Maple	All year		Less after defoliating
Japanese Maple		Less		More
Elm	Moderate all year
Flowering and fruiting	Not while blooming, will not set fruit