Stay away from peat moss, though a little wouldn't be terrible in your mix. What are you growing? If it's conifers or any acid loving tree, little bark bits are a good organic - if you can find mulch small enough, or break up the soft wood pieces in Orchid Mix(es). Compost can be added, or a little soil (with no peat in it) that's porous. Sphagnum isn't terrible, but be careful with it (see other post on it from today here).

I think the primary consideration for bonsai soils is particle size and second what those particles are made of. The reason I say that is, we cannot afford to have any significant amount of perched water in bonsai soils because of the fact that our containers are very shallow. If you build a bonsai soil from sand that is too fine, water will pass through it quickly, but a portion of the water will perch in the container and not drain. The reason that commercially prepared potting soils are inappropriate for bonsai is because they hold significant amounts of perched water - some support upwards of 4" of perched water. This means that if you used this soil in a 4" deep container or shallower, that the soil would remain 100% saturated after a thorough watering. Adding perlite or other large gritty material will not reduce the height of the perched water table until the volume of what you add approaches 65% of the o/a volume of the soil.

Water retention in soils is directly related to soil particle size. The smaller the particle size, the greater the water retention. As particle size increases, the height of the PWT decreases until at a particle size of a little over 1/10", the PWT disappears entirely. From this, we can see the benefit in trying to keep a fairly uniform particle size in that 1/10-1/8" size range. THEN, we can start to concern ourselves with the intricacies of building an appropriate soil.

I'm assuming this isn't torpedo or builders sand - like is used for mortar - right? It's a mixture of sand and mixed sizes of small gravel? If you simply screen the all-purpose sand to an appropriate size and try to use it as a soil, it would work if you were willing to stand over it and water every 15 minutes. IOW -0 there is not enough water retention. So you need to add compatible size materials that will add water retention. I use 1/8-1/4" fir bark and Turface (clay that is fired at very high temperatures so it is ceramic-like). Instead of the gravel you might use, I use crushed and pre-screened granite chips. Most of my soils are equal portions by volume of

1/8-1/4" screened fir bark
screened Turface
crushed granite in grower size or #2 cherrystone.

It looks like this:

{{gwi:7488}}

You're looking at the nebari of a recently lifted Styrax japonica (Japanese snowbell) I grew in a nursery bed from a cutting, btw.

What's nice about this soil is it's made from only 3 components. Because the grit holds little water and the Turface holds lots of water, the soil is easily adjustable for water retention by varying the amounts of Turface and granite in the mix while limiting the bark component to no more than 1/3 of the whole. It holds good amounts of water in the internal pores of the Turface and bark, yet holds no perched water.

A closer look:

{{gwi:5648}}

If you simply added peat moss to gravel you screened to an appropriate size, the moss would simply fill in the spaces between the gravel. This reduces aeration and increases water retention. Appropriate size bark would be better, but even bark breaks down, which is why I like to keep it to 1/3 or less of the total volume with the rest of the soil being stable mineral products.

Everyone has their own ideas about bonsai soils, but all ideas are not given the same amount of consideration. Simply offering "it works for me", which is commonly done, is no testimony to the comparative worth of a bonsai growing medium.

Al

Here is a link that might be useful: In greater depth - if you're interested.

Hi, that's a really good explanation, and Tapla is an expert, but I will argue against the idea of the perched water table, which has been basically disproven to be a factor in bonsai pots. Brent Walston, a leading expert in bonsai (see www.evergreengardenworks.com) has/had a really good article (or one of his blogs) on the subject last year and showed that while the idea is theoretically valid, it ceases to matter in small pots (even 'large' small ones) as the effects are reduced to such miniscule amounts as not to matter at all.

Hey, Thanks for all of the great advice. You have helped tremendously. So, where in the world do you buy turface in large bags for a low cost? Cincinnati Ohio area is where I am. I also hear that turface should be MVP grade and that just make it more difficult to find. Please help me. I dont want to pay lots of money for small amounts of turface. I have large bonsai pots. Plus isnt turface used on tennis courts? Couldnt you buy that stuff in large amounts?

Thanks,

Gardener Guy

Lucy - I'm going to issue a good natured challenge to point to something in Brent's offerings that is inconsistent with what I said, and to anything that says PWTs are irrelevant in bonsai pots. It's likely that there is something you misinterpreted on both counts and I'd like the opportunity to explain. If PWTs weren't an issue, we could all forget about bonsai soils and grow in MG or other out-of-the-bag potting mediums, but we know that's not feasible w/o a willingness on our parts to sacrifice plant vitality on the altar of convenience.

GG - if you share where you live, I'll point to likely sources of Turface MVP (or Allsport) in your neighborhood.

Al

Like I said earlier, I am from Cincinnati, Ohio. This is my area. I can shop anywhere near here. So far I found Chicken Grit (crushed granite) at a local feed store. I also found all-purpose construction sand from the hardware store that I personally sifted to take away the (sand) and now it's small pebbles. I think it works alright, 4 now. Like I said, anywhere in Cincinnati Ohio I will shop if they carry stuff that is inexpensive.

Thanks,

Gardener Guy

The chicken grit (grower size) is pre-screened and a perfect size for your soil (for all but mame size bonsai). @ $7 or so per 50 lbs, it's a steal. For Turface, try the John Deere Landscapes dealer on Mt Moriah in Cincinnati @ (513) 943-0940, Cincinnati Wholesale Supply, Fairfield, @ (513) 881-4580, Century Equipment, Hamilton, @ (800) 346-0066.

Al