pH value

pH value and water retention are some of the important characteristics to know about when selecting the soil types for bonsai.

Generally speaking, deciduous trees prefer soil with a pH of 6.5 or less. Coniferous trees, on the other hand, prefer slightly acidic soil with a pH of around 5.5.

As explained shortly the pH value is measured by adding a soil sample to a quantity of water. The resulting pH value indicates how much the soil changed the pH of the water and can be measured with a simple kit if one needs to identify this. Often in case of a problem occurring that isn’t clearly related to overwatering, lack of fertilizing, or the opposite in both cases.

If the soil pH value is too far from the ideal there is a greater risk that some nutrients and minerals will become more available, and that even to the point of toxicity, where other nutrients become less available which also leads to poorer growth.

The importance of the right pH value will vary for each species. For Azaleas and Rhododendron, it’s very important to use a low pH value for these to grow and develop well.

Some trees will thrive almost equally well in one or the pH value.

Alkaline favouring trees

Examples of trees and shrubs favouring alkaline soil above pH 7,5 are Boxwood (Buxus sempevirens and B. harlandii), Blackthorn (Prunus spinosa), Cotoneaster (Cotoneaster), Field maple (Acer campestre), Hawthorn (Crataegus), Spindle tree (Euonymus), Yew (Taxus) to mention a few.

Acid-loving trees and shrubs

Some species demanding acid soils are Azaleas and Rhododendron.

Trees that like the soil slightly acidic are Japanese maples (Acer palmatum), Beech (Facus sylvatica), Birch (Betula), Crabapple (Malus var.) for example and Pines (Pinus) which also tolerate relatively acidic soils.