The correct method for repotting and changing the soil of azalea bonsai
The usual conventional method is to tip the plant's root ball out, remove part of the old soil, trim and tidy the root system, refill with fresh soil, and water. When soil is changed this way, the slightest carelessness in management will kill the plant. The longer it has been cultivated, the higher the mortality rate. The reason is: the old clump of soil left at the base of the trunk is not only compacted but also dry, and the balance of supply and demand between the top and bottom of the plant is lost. After the plant is potted up and watered thoroughly again, water finds it very hard to penetrate into the soil clump. Even if a lot of water is poured, the water all seeps out through the new soil layer, while the middle of the root ball remains dry (azaleas are shade-and-moisture-loving plants, and most of their fibrous roots have been removed), so they easily die from loss of water. Even if they do not die, their growth is very weak.
The so-called "fixed-pot soil change" means keeping the plant fixed in the pot, without repotting and without moving the pot soil, using only an iron trowel to dig out part of the old soil and old roots and fine fibrous roots around the edges of the pot soil, then filling in fresh soil. There are two methods: one is changing the soil on one side, completing a pot in two stages over two years. The other is changing the whole pot of soil, changing the soil once a year or once every two years.
Precautions:
1. 1-2 days before changing the soil, water thoroughly once, so that the pot soil stays moist.
2. It is best to change the soil on a cloudy day or before light rain.
3. It is best to grow it in a shallow pot.
4. For the soil, choose a loose, fertile, slightly acidic leaf-mould soil.