Solving Alkaline Water Problems
By Richard Lynch, Palos Verdes Pen., California
Reprinted from the Southern California Chapter Newsletter
Like all plants, rhododendrons and azaleas need calcium but because they normally are found in acid soils with a low free calcium content, they became adapted by taking up all the available calcium. Unfortunately, when grown in alkaline conditions they apparently are unable to discriminate or to absorb only the required amount of calcium. The plants take in too much to the exclusion of other necessary elements, particularly iron and magnesium, resulting in chlorosis and, often, complete loss of the plant. A high concentration of sodium is even more toxic than a calcium concentration and, in addition, sodium binds itself to clay particles, affecting the degree of soil permeability and therefore drainage.
With the recent switchover to 100% Colorado River water by the Los Angeles Metropolitan Water District, both of the above alkaline chemicals now are contained in larger percentages in our water supply. Colorado River water has a mineral content of 700 mg per liter compared with Feather River water containing 300 mg per liter. Feather River water was used from 1972 in most areas of the Los Angeles basin until March 1, 1977 when it was discontinued. Sodium has increased from 36 mg per liter to 108 mg per liter, and calcium from 34 mg per liter to 82 mg per liter. Hydrogen ion concentration or pH has increased from approximately 7.8 to more than 8.0.
Problems arising from this increase in alkalinity will show probably as one or all of the following:
1. Chlorosis: older, mature leaves will turn yellow except for green lines along the leaf veins;
2. Salt burn: brown tips and margins of leaves;
3. Growth depression: lack of general growth and bud set plus inability to use fertilizer and sometimes in conditions of advanced chlorosis, fertilizer burn.
(Refer to "Sodium Salts and Hardy Varieties of Azaleas," by Tom and Julius Nuccio Jr. In September, 1976 (Vol. 1, No. 2) Newsletter of the Southern California Chapter ARS)
The common solutions generally offered for these problems are leaching and/or sulfur applications, both of which have limited effectiveness. Leaching is a rather crude approach in that it results in washing away nutrients as well as some salts and replacing both with more salts. Sulfur applications are always ""after the fact" and very imprecise.
A better alternative is to try to solve the problem during irrigation by chemically neutralizing the effects of sodium and calcium before they can damage the plants. The method proposed here is to use a siphon or similar device coupled to the sprinkler system or garden hose to meter and deliver dilute sulfuric acid with the irrigation water to achieve the following:
1. Reduce pH from 8.0 to 5.0.
2. Cause the sulfuric acid to combine with the insoluble calcium carbonate and bicarbonate to produce soluble calcium sulfate (gypsum).
3. Initiate the secondary effect of lowering sodium concentration by causing the calcium sulfate (gypsum) ions to reverse the toxic processes of sodium. They replace sodium ions on soil particles and sodium also is carried down below plant roots as soluble sulfate.
At present, no really inexpensive siphon system capable of working with garden sprinklers has been tested satisfactorily. Pending further investigation, the following remarks are directed toward hand-held hose use.
The "Syfonex" made by the Hydroponic Chemical Co. of Ohio, which retails for around $4.50 in most nurseries, is a brass siphon which attaches between the water tap and the hose. It is equipped with a rubber tube to suck up concentrate from a pail in a ratio of 16 to 1 and is very simple to use.
Dilute (38%) sulfuric acid is available for swimming pool use at Safeway markets in one gallon containers. (Do not use muriatic acid which is hydrochloric). The sulfuric acid should be used at the rate of one tablespoon per gallon of water to lower pH one unit (assuming average water pressure of 40 to 45 pounds). The hose nozzle must be in its most open or unrestricted position during this operation for accurate metering. If no nozzle is used the acid strength should be reduced to one-half tablespoon per gallon of water to reduce pH by one unit. It is suggested that a pH test be performed on the water being delivered from the hose before plant irrigation to check metering accuracy and as a precaution against applying too acidic a mixture. Swimming-pool strength sulfuric acid is fairly weak but still extremely corrosive and should be used carefully. As a further precaution the concentrate should be well shaken prior to siphoning and no more than four tablespoons of sulfuric acid ever should be added per gallon of water.
It is hoped that the application of the above outlined procedure will result in more successful cultivation of these beautiful plants in our current, rather difficult environment.