In Defense Of Solid Fertilizers

Fertilizer adventures are a given in most bonsai gardens. For years I used solid organic cakes, being the traditional solution, but found the birds unmanageable in their hunt for grubs underneath them. I wasn’t willing to use insecticide to control fly larvae, so birds, and lost fertilizer, were my fate for a while.

Now there’s a cat in the garden. It’s a quite well-fed one, with a dragging belly (and no piles of feathers anywhere), but she’s apparently a sufficient talisman of ‘Don’t you even THINK of flipping a cake off that pot!’ We’ve increased her pension plan.

Now I’m back to my preference, organic cakes.

If you’ve read Bonsai Heresy, you may remember one chapter where I write about fish emulsion being our primary fertilizer. But the most important sentence comes right after it: ‘If my situation were different, I’d likely use cakes for their multiple benefits and ease of use.’ Yet now all I get are questions about our fish emulsion schedule.

One of the fears of any technical book author is that the most important sentence will be missed, and the least important remembered. The fertilizing chapters of Bonsai Heresy are full of such awkward potential.

If possible, go with a slow release, solid fertilizer. Organic cakes if possible, maybe chemical pellets if not, or try fish emulsion or maybe a mild chemical liquid. We’ve all got different yard variables, and so our fertilizing choices will likely differ, too.

Slow release works great for our process. A little bit gets in every time we water. Equally cool, slow release fertilizers resist flushing out. We can flush liquid fertilizer out with watering, and rain can flush it out, but slow release solids keep fertilizer levels steady regardless. Infrequent use of mild liquids often ends in pale, weak looking bonsai. You can use liquids, just be aware it’s often a lot more work.

In general, I’d say if confused by anything you’re reading, don’t blame yourself, blame the author. It’s what I do.

Bonsai Heresy illustration by the great Sergio Cuan. Sailor tattoos on bonsai should be commonplace.


  1. Michael Corbin says:

    Do you buy cakes or make your own? I have been using plantone and Holly Tone in tea bags with decent results. No birds but sometimes they get stolen by critters.


    • crataegus says:

      Both buy and make ours. Tea bags can be a big help to keep things together, especially if the pellets are small or to contain breakdown. They do add one more thing to do, though, and in my big yard we don’t have the time…

  2. Ray says:

    Ahh yes the many variables of liquid vs solid vs chemical vs organics aaargh, It’s a mad, mad world out there Michael, tread carefully and watch out for nargels.😂😂😂

  3. John says:

    I agree that an organic slow release is the most controllable situation. Yet Chemical pellet slide release is my preference as a base fertilizer.
    This decision is due to the downside of the organic slow release cakes “dissolving” and gunking up to media much faster… the issue is outta sight, yet impeding the porosity of the media. One doesn’t notice this slow to form issue until realizing that water isn’t percolating as fast as it should… or hardly at all.
    The half measure to solve this has been the removal of the top 1/2-1” ir so off the media, which just hides the deeper issue for awhile and can compress the media immediately below…which is getting gunked up to a lesser extent. The full solution is a total repot every couple three years, especially when using akadama or kanuma based soils.

    • crataegus says:

      Chemical pellets work well, and they are preferred by many. We use some Osmocote. They only work well if there’s enough of a lip on a pot to keep them from washing away, though. I’ve not had much luck with them on mounded plants with no lip. The cakes stay put but can create a problem, as you say. Tamahi and others hold together pretty well though, and don’t gunk up the top surface as much has others. Better binder, I assume. Biogold, though plants like them, make a big mess on breakdown. No plan with fertilizing is without a problem. We choose our problem! Some soil cleanup is necessary for any solid organic fertilizing.

  4. Michael, spanish reader here. Read Heresy already. Wonderful book, love the 56 small chapters format, it is perfect for later easy reference. I have a question. Last summer I tried Tamahi without sphagnum to dissolve it and It just stayed there without fermenting. This year I tried biogold with sphagnum and it went the other way around. Biogold was dissolving so fast with contiuons moisture that water through drainage was brown! How do you guys apply biogold? Sphagnum to help dissolution or not?

    • crataegus says:

      It didn’t ferment? That’s curious. Do you live in an arid place? I had that problem in Arizona. Here in Oregon they stay together but do crack and let water in. They stink a little, so they’re decomposing. Biogold isn’t my favorite…it creates a lot of algae, mucks up the surface a lot, and is really expensive, but the plants love it. I like the Tamahi type fertilizer. You can make your own. What do you mean by sphagnum dissolving it? Keeping it moist?

  5. bonsai_bentley says:

    Interesting topic. I tend to do both a pelletized fert (Bio-gold) and a weekly fish emulsion/kelp mix during the growing season. Once the heat starts to come in I stop applying either one.

    • crataegus says:

      It’s a good combo, I’m sure it works well. Above 90 F being cautious with fertilizers is wise, especially with chemical.. With organics there might be more latitude—in Japan there are often piles of cakes on trees at 90 and above, and the trees are lush and don’t look like there’s any fertilizer burn issue. Just an observation.

  6. vonsgardens says:

    Mike, have you tried your osmocote in tea bags on mounded plant?

    • crataegus says:

      It’s a fine idea, and I think it’d work well. I’ve got a garden that is open to visitors and so aesthetics are a part of the question I try to answer with either organics, which are less obtrusive, or in some cases liquids.

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