Article 27 – ‘The pH factor (Part I)’

The first signs of demise

Bonsai either given as a gift, individually purchased or one cultivated by other means, grafting, a cutting or from seed is usually lavished with care and attention to ensure its health and vitality. As the seasons progress new buds flowers and or fruit appear, enhancing the tree’s ruggedness and or beauty, a wonderful miniature specimen of its full size counterpart. But things begin to change, autumn is still a long way off, the tree’s leaves start to turn yellow and this is the first sign that something is not as it should be and questions start running through ones mind.

  • Was it watered enough or too much  
  • Was it given the correct type and quantity of feed
  • Should it have had full sun or partial shade
  • Has it been attacked by pests or disease
  • Did it need re-potting
  • Was it pruned at the wrong time of year

One then resorts to searching the world wide web looking for answers in trying to solve the problem/s, but how can we resolve the problem if we don’t know what it is. The above mentioned questions may have something to do with the tree’s poor state of health or potential demise, but not in every case. Arguably the main contributing factor causing a tree to wither and die is the medium or soil composition in which the tree is planted.

Acidic to alkaline

Soil contains a multitude of living organisms that consume, digest, and cycle nutrients. These living organisms include archaea, bacteria, actinomycetes, fungi, algae, protozoa, and a wide range of insects for example. Mites, nematodes, earthworms and ants all of which are important to the vitality of a soil composition, which in turn is vitally important to any and all growing mediums. But if these much needed organisms have expired, then the soil is effectively spent and of little use. However, the lack of organisms although of great importance is not the only issue, what is just as important is the type of soil composition and its pH content.

For example, some species such as Rhododendrons and Azaleas family Ericaceae will only survive in acidic soils. Whilst others the common Beech Fagus sylvatica and Hawthorn Crataegus laevigata prefer alkaline and some can be borderline, Cotoneaster family Rosaceae and Hazel family Corylaceae. But how do we know what kind of soil is correct for our particular bonsai? pH is measured from 1 to 14 and if we consider that a pH of 7.0 is neutral, all above will be alkaline and all below will be acidic, as shown in the following chart for the most common species found in bonsai.


pH chart.1

pH chart.2

pH chart.3

As the chart indicates most trees will survive in soil which has some degree of acidity up to a more neutral range, whereas others can tolerate a more alkaline based composition. To give a clearer definition consider the image below, which gives an indication of the acidic and alkaline values and the pH tolerance zone for most plants.

Soil pH graph

In the next article of ‘The pH factor’ (Part II) we look at soil differences, the possibilities of changing their pH content and a brief look at soil pH testing devices. Until next time BW, N.

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