Bonsai is the ancient art of growing miniature trees in containers. One of the keys to successfully growing bonsai is using a well-draining yet nutrient-rich soil mixture suited for the specific species of tree. Buying premade bonsai soil can be expensive, but you can easily make your own soil tailored to your bonsai trees. Read on to learn all about the components of bonsai soil and how to mix and prepare different recipes.
Understanding Bonsai Soil
Unlike the soil found in gardens and landscapes, bonsai soil is specially formulated to provide the ideal environment for growing miniature trees in containers. Here are some key characteristics of quality bonsai soil:
Fast draining – Bonsai soil must drain quickly to prevent root rot since it is planted in a confined pot.
Aeration – Good aeration allows oxygen to penetrate the soil and reach the roots.
Moisture retention – While well-draining, bonsai soil must also retain some moisture and nutrients to sustain the tree.
Small particles – Finer soil particles provide more surface area for roots to access nutrients and moisture.
pH balance – Most species thrive in slightly acidic soil with a pH between 5.5 and 6.8.
To create the perfect bonsai soil blend, you need the right combination of inorganic and organic components.
Inorganic Components
Inorganic materials make up the largest portion of bonsai soil, providing structure and ensuring excellent drainage. The most common choices include:
Akadama – Considered the gold standard; these baked clay granules from Japan help retain moisture and nutrients. Pricey when imported but excellent for most species.
Pumice – Lightweight volcanic rock that creates aeration and drainage. Use for conifers and other trees that demand sharp drainage.
Lava rock – Irregular, porous red/black particles made from volcanic lava flows. Retains less water than akadama but improves drainage.
Haydite – Lightweight ceramic clay granules fired into hard artificial stones. Adds weight and structure while creating porosity.
Diatomaceous earth – Silica particles composed of fossilized diatoms. Improves drainage and provides silica for plant growth.
Perlite or vermiculite – Light, porous minerals that aid with aeration and moisture retention when mixed with other components.
Granite grit – Crushed granite grit provides structure and weight for large, heavy bonsai specimens.
Sand – Coarse sand particles improve drainage quickly. Avoid beach sand which contains salt. Opt for river sand or horticultural sand.
Organic Components
While inorganic materials form the bulk of bonsai soil, organic matter is also vital to provide nutrients for trees. Good choices include:
1.Sphagnum peat moss – Adds moisture retention and slow-release nutrients. Helps buffer soil acidity.
2. Compost – Nutrient-rich, decomposed organic matter improves moisture retention and nourishes trees.
3. Bark fines – Finely shredded tree bark adds texture, drainage, and space for air pockets. Decay slowly over time to release nutrients.
4. Coconut coir – Better water retention than peat and provides micronutrients. Made from coconut husk fibers.
5. Worm castings – Nutrient-dense worm manure full of microorganisms, enzymes, and trace elements that enrich soil.
6. Leaf mold – Decayed leaves add organic matter. Chop finely before incorporating into soil.
7. Organic fertilizer – Well-composted manure, bone or kelp meal provides a slow but steady source of nutrients over time.
The ideal ratio for most bonsai soil recipes is 75% inorganic materials to 25% organic matter. The percentages can be adjusted based on the specific drainage and nutritional needs of different tree species. Conifers often thrive in a higher percentage of inorganic substances like pumice or lava rock while broadleaf trees like maples may need more peat moss and compost.
Basic Bonsai Soil Recipe
Follow this straightforward formula to create a versatile, well-balanced bonsai soil suitable for many indoor and outdoor species:
50% pumice, haydite or lava rock – Provides structure and fast drainage
25% akadama – Contributes moisture retention, porosity, and nutrients
20% bark fines or coconut coir – Adds organic matter to support plants
5% sphagnum peat moss – Retains moisture and creates acidic pH
Pinch of Osmocote slow-release fertilizer
Mix thoroughly while dry before using
This recipe works well for common bonsai trees like jade, birch, elm, oak, maple, juniper, pine, spruce, and fir trees. Adjust the ratios or components as needed to suit your specific plant.
Soil for Conifers
Conifers like pine, spruce, juniper, and cedar trees perform best in soil with extremely sharp drainage. Aim for a higher percentage of inorganic substances like:
75% pumice or lava rock
20% akadama or haydite
5% bark and peat
Avoid richer organic matter which may hold excessive moisture and lead to root rot. Fertilize carefully as conifers are sensitive to overfeeding.
Soil for Tropical Trees
Tropical and subtropical bonsai trees such as jade, fig, olive, elm, and some maples appreciate more moisture retention. Create a good tropical soil recipe with:
50% akadama
25% lava rock or expanded shale
15% fine bark
10% sphagnum peat
Pinch of granular fertilizer
The increased peat and akadama will help store water and nutrients in the warm, sunny environments tropicals prefer. Larger particle sizes improve drainage for species that dislike wet roots.
Customizing Your Soil
The ingredients and ratios of your bonsai soil can be customized to meet the needs of your individual trees. Here are some variations to consider:
More sand for cacti and other desert plants that demand fast drainage in arid climates.
Additional peat moss for azaleas, camellias, rhododendrons, and other acid-loving plants.
Extra perlite or vermiculite for seedlings and young trees still developing roots.
Increased compost ratio for trees with high nutritional demands like maples and fruit trees.
A sprinkle of lime if pH needs to be raised for trees that prefer alkaline soil.
Less or no sphagnum for Mediterranean trees adapted to fast-draining mineral earth.
Substitute calcined clay for akadama when not available.
Use granite grit chunks for heavy trees like oaks and olives to add weight in pots.
With the right balance of aggregate, organic matter, and amendments tailored to the tree, you can create an ideal bonsai soil. Test and adjust recipes as needed to achieve excellent results.
Preparing and Storing Bonsai Soil
Once chosen ingredients are measured out, there are some important steps to take before potting up bonsai trees in homemade soil:
Mix all dry components thoroughly before introducing moisture. This ensures particles are well integrated.
Disinfect reused soil by baking at 220°F for 30 minutes to kill pathogens. Let cool before using.
Moisten soil before use. Dry soil can wick moisture away from new roots. Mist lightly and mix.
Consider leaving rich soil to mellow in the open air for several weeks to stabilize pH and nutrients.
Store extra prepared soil in breathable containers like cloth bags or plastic colanders. Keep covered and away from rain.
Conclusion
By following the expert techniques used for generations, you can easily create custom bonsai soil for your treasured trees. Mixing your own blend gives you control over the ingredients and ratios to meet each plant’s specific requirements. Both new and experienced bonsai enthusiasts will appreciate the ability to prepare excellent soil at home for a fraction of the cost of commercial mixes. With the proper bonsai soil and careful cultivation, you can grow happy, healthy miniature trees for many years to come.