Potting soil and media

Potting soil and media
The quality of the soil determines whether your potted plants will be healthy and vibrant. According to experience, unhealthy and dying potted plants are mostly planted in poor soil (mostly organic soil), or even worse, are planted in general gardening soil. Gardening soil tends to harden, which can hinder the growth of potted plants and even cause serious damage.

A good soil mix needs to have the following properties:

Good water retention
The soil must be able to retain enough moisture so that the potted plant can have sufficient moisture between waterings.

good drainage
Excess water must be drained out of the basin immediately. Soil that does not drain well and retains too much moisture will prevent aeration and allow salt accumulation. Excessive moisture in the root system will cause rot and the potted plant will not survive.

good breathability
A good soil mix will have enough space and air between the gravel. In addition to oxygen, plant roots also need good flora and mycorrhizae (a symbiosis between fungi and plant roots), so that they can produce enough food for root hairs to absorb and transmit to the leaves for photosynthesis.

Organic or not?
Soil selection is divided into organic and inorganic. The decayed material of dead plants such as peat, fallen leaves or bark is called organic soil. One concern with organic soils is the disintegration of organic material, which makes drainage difficult — although the rate of disintegration varies (pine bark is better at mixing it into the soil). Most humus soil can hardly retain moisture after it is completely dry; this is why commercially available cheap potted plants have a hard time surviving, because most of the water poured directly flows out of the pot.

Inorganic soil contains only trace amounts of organic matter or even no organic matter at all, such as volcanic lava rock, calcite, or high-temperature sintered clay. These media not only do not absorb a large amount of water and nutrients (compared to organic soil), but also Provides good drainage and breathability.

Well-structured, granular inorganic soil drains quickly and maintains good aeration. Tight and solid organic soil lacks gaps for drainage and ventilation, which can easily lead to root disease or root rot of potted plants.

soil composition
The most common potting soil ingredients are akadama soil, Kanuma soil, lava rock, as well as humus soil, fine gravel or river sand.

Potting Soil Composition
From left to right: humus soil, red jade soil, kanuma soil, lava stone
Akadama soil is Japanese clay that has been calcined at high temperatures to become hard. It is specially used for potting and is easy to obtain. It is sold in potting and gardening stores (online and physical). Must be sieved before use. It should be noted that akadama soil begins to disintegrate and pulverize in about 2 to 5 years (depending on the quality), which will affect ventilation. Therefore, when using akadama soil, you need to change the pot frequently, or mix it with other materials with good drainage. Medium (such as Sichuan sand). Check out the bonsai forums to find out which brands are common in your area.

Kanuma soil is a kind of soil formed by the natural deposition of volcanic ash. It has a soft texture and is good at retaining water and nutrients. Mixing Kanuma soil into the soil can help retain moisture and promote root development.

Mixing lava rock into your potting soil medium increases water retention and also strengthens the structure. Roots cannot grow into lava rock.

Organic humus soil contains peat moss, pearlite, and sand. Its disadvantages are poor drainage and airtightness; but it is very useful when used in mixed soil.

Gravel mixed into the potting soil can provide excellent drainage and air permeability. It can also be used alone in the bottom layer of the pot to enhance drainage. However, many experts no longer do this and only use Akadama soil, Kanuma soil, and lava rock. Just mix the stones.

Potting Soil Mix Recommendations
Different tree species require different soil mixes. Please go to the Potted Tree Species Guide to find out the most suitable soil mix for each tree species. There are two main soil mixes that beginners can start with, one for deciduous plants and one for coniferous plants. Both soil mixes contain Akadama soil (water retention), Kanuma soil (structure), and lava stone (breathability and drainage).

Be sure to adjust the two soil mixes to a ratio suitable for your environment. If you are unable to check your potted plants at least twice a day, use more Akadama soil (or add humus soil) to increase water retention. If your environment is humid, use lava rocks (or gravel) to increase soil drainage.

(If the medium is difficult to obtain, you can use a mixture of red jade soil and Sichuan sand. Beginners can use 50% of each. When you are familiar with your potted plants, you can make appropriate adjustments on your own.)