wood chips in bonsai soil affect pH

castorcrap(z5 wv & z6 Md)April 2, 2006


I have just completed sifting perlite, lavarock, drystall, and fired clay. The mix looks good, but lacks organic matter. Ive looked through all my books, it seems they use peat for organic matter. But how do you sift it, because if you keep sifting it, it all becomes dust and goes through? So then I took some soil conditioner (smells like its made of ground up pine mulch) and sifted out the larger peices and used them. Will the pine bark will be too acidic? Should I use peat instead, even though its particles are very small and will fill in between my pourous mix? What about introducing mycorrizae some how? Due to being a med student and possibly not having time to water every day, would using a 50% standard potting soil/ 50% inorganic mix, work, or would this be too much dirt and would defeat the whole purpose of even attempting to make bonsai soil?

Thank you for any help you can offer,


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Don't use peat period. Definitely use pine bark for just about anything, up to 2/3 of the mix for conifers, though you can use good compost for maples, gardenias, things that prefer more alkali. A 50/50 mix is good for e.g. elms, but will be too 'organic' for conifers usually. In summer, you're going to have some pretty hot stretches there, and if you have anything growing in little pots, even pine, I hope you'll be around to keep an eye on them because it can take less than a day for the heat to do them in. One good idea is to lean a white or reflective thing against the pot to keep it and the roots cooler. I sometimes put my pots into a regular window box to shade them.

    Bookmark   April 2, 2006 at 12:24PM
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castorcrap(z5 wv & z6 Md)

Thanks lucy,
At this point, none of my trees are in small pots because they need to grow more, and it helps me avoid having to water them real often. Should I sift & discard the small particles out of the potting soil that I use to make the 50/50mix of potting soil and inorganic matter, or just use the soil strait out of the bag?

    Bookmark   April 2, 2006 at 2:29PM
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tapla (mid-MI z5b-6a)

Bonsai soils are more about the physics of the soil than they are about what material the particulates are mad from. In most cases, we avoid peat because it is small enough that it collects in macro-pores, turning them into micro-pores that hold water instead of air. In my estimation, compost is worse than peat because it holds water tighter and its water release rate is slower. Plus, peat and compost break down too quickly to be of value in most soils for bonsai.

Particles of a uniform size and shape will yield best drainage. Experiment: In a clear bottle, add a hundred or so large marbles - the boulder type, twice as large as a regular marble. These fill a 2 qt clear container and represents a soil with uniform size particulates and plenty of air spaces, a beautiful thing, this soil. Then, take a quart of BBs, dump it on top of the marbles and give it a little shake. The BBs find their way into the large pore spaces, but still fit handily into the "full" bottle. Then, pour a quart of sand (you can substitute the word peat or compost for sand here, too) into the "full" bottle. The sand filters down, clogging the remaining air pores and making the soil a terrible choice for plants. Sand is death to aeration and how did I get 4 qts of soil in a 2 qt bottle? By jamming small particulates into my air-holding macro-pores.

You can build a wide variety of soils if you have a few things on hand. A porous mineral product that holds air, moisture, and nutrients - like Turface, Haydite, akadama, pumice, others. An irregularly shaped mineral product, preferably with rough or jagged edges that doesn't hold air or water - crushed granite or large silica (almost BB size) is good here, and an organic component in a suitable size that will resist rapid breakdown by soil organisms. We often use conifer bark to fill this requirement because the combination of a high % of lignin and suberin (in the bark) makes it difficult for micro-organisms to cleave hydrocarbon chains and destroy the structure of the organic part of your soil.

I can't think of anything I grow in bonsai soil (houseplants too) that I use more than a 1/3 organic component on. I usually keep a large amount of soil that is 1/3 each of Turface, crushed granite (grower grit), and screened fir bark. I amend this basic mix as needed. Your mix may vary & use other ingredients, but this one won't be too far from what will work well for you.

I grow most deciduous plants in the equal parts mix. Pines & junipers I use up to 90% inorganics in the soil. I even have a few plants that are perfectly happy in 100% Turface. Experiment, but don't be tempted to compromise your soil mix too much to simply extend intervals between watering - your plants will pay.


    Bookmark   April 2, 2006 at 2:35PM
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Hi, I think I wasn't very clear on one thing - when I mentioned a 50/50 mix, or compost, I meant 50/50 organic and nonorganic (grit + compost - instead of grit and peat), for things like elms, etc.

    Bookmark   April 2, 2006 at 4:10PM
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tapla (mid-MI z5b-6a)

Opinion only, but glad to discuss this: I never use compost in any container soils. It retains too much water, destroys aeration, slows drainage, and adds nearly nothing in the way of nutrients. There are too many good, and stable components out there to select one that makes more work out of successful growing than necessary. What sense to go through the effort of building porosity into a soil by carefully selecting some components, only to destroy it with the addition of the next?


    Bookmark   April 2, 2006 at 5:10PM
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Our summers are very hot and dry. I have experimented with several mixes and found I have to use organics to keep my pots from drying out in the summer. Winters inorganics are fine of course but I just have to pay a close eye on my watering practices then. JMO.

    Bookmark   May 16, 2007 at 3:02AM
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Whatever works - we're certainly not all in the same boat and if you can be flexible about what to use, it's a lot better than being knee-jerk about 'mix #3' being the only 'right' one.

    Bookmark   May 16, 2007 at 4:34AM
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Thanks. That was the kind of explaination I was looking for in my "Bonsai Soil Confusion" thread I posted about a month ago. Very clear and lucid demo without the mumbo jumbo I find in the books - some of which recommended adding garden soil and peat.

After I posted the mentioned thread, I talked to some of the members of the Atlanta Bonsai Society at a workshop, and have been using their advice: growers grit or perlite and crushed sieved pinebark for my soil with a top dressing of NZ sphagnum - so it doesn't wash away when watering.

    Bookmark   May 18, 2007 at 3:40PM
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