Kusamura Bonsai Club
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Adapted from material by John Planting |
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There are many different soil mixtures used to plant bonsai. Bonsai people in Brooklyn, Scotland, Holland, Japan, Canada and California all have different growing conditions and different materials available to make soil mixtures. Most mixtures have one thing in common -- they don't use garden soil. This is because shallow pots don't drain as well as soil in the garden and as a result the roots can stay too wet and rot! These recipes describe "soil mixes" that we've found work in the micro-climates around Palo Alto, California. If your weather is warmer or cooler than Palo Alto you'll need to modify the mix slightly. This is explained later. While these recipes were created by several of our club members working together, these aren't the only recipes being used. Some club members use different proportions or substitute materials (e.g. using decomposed granite instead of sand or pumice instead of Kanuma). These recipes are intended as a starting point. Soil Size The size of the particles used is important. For example, a mixture made with larger particles will drain faster than a mix made using smaller particles. A small pot will have less soil and tend to dry out faster than a larger pot. We can keep a small pot from drying out too quickly by using smaller sized soil particles in the mix. The table below suggests the size of particles to use for different size pots.
Soil mixture is made by first sorting the various materials (see tables below) into the proper size and then combining them. Sorting is usually done using a sieve such as shown below. Sieves typically come with three screens that allow you to sort your materials into the proper size according to the table above.
Making Soil Here's the procedure for making a "soil mix". First, sift each material three times. First, sift with the largest screen and keep the material that doesn't fall thru the screen into one pile or bucket. Now use the medium screen and again sift the material that went thru the largest screen -- keep the material that doesn't fall thru the screen into another pile or bucket. Now use the finest screen and sift again -- keep the material that doesn't fall thru the screen into a third pile or bucket. Only very small particles or dust will go thru this screen keep this dust to make Muck (described below) or discard. Now that you have each of the components sorted into three sizes, combine them in the rations shown in the tables below. For example, if you need soil mix to pot a black pine follow the ratios for Conifers.
Putting Soil in the Pot Generally you will put a shallow layer of soil in the bottom of the pot, put your bonsai in the pot and add the same size soil on top of the roots. For example, if you are planting a black pine in a rectangular pot 12" x 8" x 2" deep, you would use 3/8" size soil. However, when pots are deeper than 3" it seems to be valuable to use a layer of larger soil in the bottom to make the soil drain faster. This is shown in figure 2. BTW: Kathy Shaner recommends replacing the top inch of soil once or twice a year. This gets rid of a lot of weeds and salt build-up. Simply use a chopstick or small rake and gently rake the surface over the edge -- be careful not to damage any roots. Then put fresh soil on top and use a chopstick to settle it in around the roots.
Adapting for Other Micro-climates If your micro-climate is warmer than Palo Alto (e.g., San Jose or Gilroy) you'll want to modify the mix so it holds more moisture. For example, by adding more Akadama and/or sand and less lava and pumice. But, if your micro-climate is cooler / moister (e.g. Seattle) you'll want to modify the mix so it holds less moisture. In this case use more lava and/or pumice and less Akadama and sand. Suppliers Some of these materials are difficult to find, so here's a table of reliable sources.
Muck is another important "soil" mixture. It is a paste that's used as a binding agent to hold soil or objects such as rocks stable in the pot until the tree roots are established. When we use a rock slab (e.g. slate) instead of a pot, we often use Muck to create an edge that will prevent the soil mixture from sliding off. To do this, roll muck between your hands until it looks like a rope, perhaps 1/2 inch in diameter. Then lay the rope on top of the rock slab and arrange it until you like the shape. It usually should be irregular in shape. Now press it down until it sticks to the rock slab. Now add your trees and soil mixture. Recipe: Sift adobe soil, keeping only the fines (dust to 1/8"). Use a screen that's the same size as window screen or slightly smaller). Some peat moss is long and fibrous. If this is yours, cut it using scissors into lengths approximately 2" in length. Now mix half adobe and half peat moss. Add just enough water that it can be kneaded to a dough-like consistency. It's easy to knead if you put the mixture into heavy-duty zip lock bag. Hint: If you can find black adobe that will look best, but it's difficult to find. In fact, depending on where you live any kind of adobe soil may be difficult to find. If you are using Akadama in your soil mix you are probably throwing away the dust when you sift it. Don't -- use it in this recipe instead. Storage: If you have any left over, store it in the zip lock bag in your freezer. (Yes, your freezer. This will keep it from becoming moldy.) When you need it for your next project just remove from the freezer, let it thaw, add a bit more water if needed and then knead it a bit to get it flexible and ready for use.
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Soil
Basics
