THE EFFECT OF ALUMINUM SULPHATE ON RHODO.- 
DENDRONS AND OTHER ACID-SOIL PLANTS? 
By FReperick V. COovILLE 
[With 18 plates] 
INTRODUCTION 
Our native rhododendrons do not thrive in ordinary fertile garden 
or greenhouse soil, but they grow with great luxuriance in sand 
mixed with peat, or with rotting wood, or with half-rotted oak 
leaves. It is clear from many experiments heretofore made by the 
writer that, although both these types of soil contain an abundance 
of plant food, the rhododendrons thrive in the peat and sand mix- 
ture because the chemical reaction of the soil solution is acid, and 
they die in the ordinary fertile garden soil because the reaction is 
neutral or alkaline.2 (Pl. 13.) Except in acid soils, most rhodo- 
dendron plantings are failures. In nonacid soils the plants often 
subsist for a year or two on their old rootball of peat, but when 
that is used up they sicken and die if the surrounding soil is neutral 
or alkaline. 
The statement had been going around among nurserymen that 
rhododendrons could be made to thrive in an ordinary fertile soil 
through the application of magnesium sulphate, commonly known 
as Epsom salts, and at the suggestion of Harlan P. Kelsey it was 
determined to try the experiment. Knowing that one of my col- 
leagues, C. S. Scofield, had been using various sulphates in a re- 
markable series of experiments on the alkaline irrigated soils of the 
western United States, I asked his opinion regarding the probable 
action of magnesium sulphate in a rhododendron experiment. He 
replied that if magnesium sulphate would tend to bring about an 
acid reaction in an alkaline soil, aluminum sulphate should do it a 
great deal better. Aluminum sulphate therefore, happily, was 
included in the experiment. 
1An account of the earlier experiments here described was published March 24, 1923, 
by the American Horticultural Society, as their Bulletin 1, under the title, “The effect 
of aluminum sulphate on rhododendron seedlings.” 
? See also “ Experiments in blueberry culture,” issued as Bulletin No. 193, Bureau of 
Plant Industry, 1910, and “The formation of leafmold,’’ published in the Smithsonian 
Report for 1918, pages 333 to 348, also separately printed. 
369 
