HIBISCUS
Queen of the Flowers

CHAPTER FOUR

What is pH and What Does it Mean?

Observation of plant growth in various parts of the garden is suggested, but this does not give the complete answer to the soil problem. Plant nutrient content of the soil can be determined through chemical analysis, but again this is only one of the factors that bears directly on fertility. Soil acidity, organic content, and drainage are also items which must be taken into account.

Hibiscus need a neutral to slightly acid soil and there are kits available for testing the soil. These are not expensive and could be of great advantage to the home gardener. One inexpensive kit available is "C.S.I.R.O. Soil p.H. Test Kit" which contains an information booklet, all testing gear and note book to record tests, and sells for approximately $9.00-$10.00. (circa 1980!!)

A soil test has practical value for the.hibiscus grower, it enables him to garden more intelligently. There is an advantage for the home gardener who follows the soil test recommendations. They enable him to make appropriate choices in purchasing fertilizer and other needed materials. The best use of time, physical effort, and plant care, plus protecting the investment in fine hibiscus plants, greatly increase the personal gain to be derived from the soil test. It is the first step toward soil improvement and better hibiscus. Don't sample unusual areas such as wet spots, burn piles, recently fertilized areas, or parts of the ground where pesticides have saturated the ground, as they will give an incorrect reading because of the unusual chemical content of those areas.

What does pH mean? You see it in many garden books. Written with a small "p" and a capital "H". It is a scale expressing the acidity or alkalinity of something, in particular referring to soil or a solution of blood or body fluid, etc.

Acidity is a measure of Hydrogen ion concentration, while alkalinity is a measure of Hydroxyl ion, such as Carbonate, etc. To really understand all the ins and outs of this can be a little technical for the average gardener.

In other words the pH of the soil depends on the chemical composition of its ingredients such as mineral content of rock, and the origin of the organic material content from decomposed matter from plant or animal organisms.This is what determines the pH of soils.

The pH value of the soil is an extremely important property, as it controls root activity, fertilizer availability and the production of plant poisoning Salts of Iron and Aluminium. The correct pH depends on the type of plants you intend to grow in your garden. Do they like acid soil. Or, do they like alkaline (limey) soil.

pH Scale is a set of numbers from 0 to 14, Zero (0) being extreme acid conditions. The middle point being pH 7 is a neutral state which is neither acid or alkaline. pH 14 would be extreme alkaline, so it can be seen that with pH 7 the scale of acidity increases the further it goes below pH 7 and alkalinity increases the further it goes above pH7. Recommended pH for growing hibiscus is about 6 to 7.

Colour pH Equivalent Blue-Green 7.5 Slightly Alkaline Green 7.0 Neutral Yellowish Green 6.5 Slightly Acid Yellow 6.0 Slightly Acid Orange 5.5 Moderately Acid Orange-Red 5.0 Very Acid Red 4.5 Extremely Acid

If the soil test shows that the pH is 7.5 or more (alkaline), use sulphur, iron sulphate, manganese sulphate, or aluminium sulphate to lower it. If your soil is too acid in reaction (less than 5.5), it may be rendered alkaline by the application of agricultural lime or dolomite once or twice a year. Specific advice on these matters should be secured from your garden centre or your Department of Primary Industries.