ACID-SOIL PLANTS—COVILLE 3881 
acidity it is deficient in plant food. When such a peat is used, nourishment 
for the plant must be supplied in some other component of the soil mixture. A 
very light peat of this kind, imported from Burope, consisting chiefly of 
brown fragments of sphagnum moss, is much used in the United States as a 
mulch, as an ingredient of potting mixtures, and in cutting beds, for acid-soil 
plants. It is well suited to these purposes, but being deficient in plant food it 
should not be used alone, or with sand only, as a potting soil. 
A sharp distinction should be made between half-rotted oak leaves and the 
ordinary compost of leaves with manure, garden soil, and garden trash. Such 
a compost is neutral or alkaline in reaction and should not be used on acid-soil 
plants. Sugar maple, elm, and linden leaves rot rapidly and so soon reach the 
alkaline stage that they also are not desirable for application to an acid-soil 
planting. Oak leaves, especially red oak leaves, rot slowly, and in two or 
three years, if the pile is turned over several times, make a good substitute for 
upland peat.* 
No manure, lime, or wood ashes should be applied to rhododendrons or 
other plants that require an acid soil, for all these substances tend to neutralize 
the necessary acidity. Cottonseed meal, ground soybeans, and spent malt, all 
of which contain a large amount of nitrogen in organic and acid form, are 
excellent fertilizers for acid-soil plants. Experiments made by the writer in 
the spring of 1926 show that skimmed milk and buttermilk are useful as fer- 
tilizers for acid-soil plants.” Undoubtedly the partially dried forms of these 
products now marketed for poultry feed are also serviceable as fertilizer for 
such plants. The warning should be given, however, that skimmed milk con- 
tains about ten times as much lime as cottonseed meal and that the possible 
cumulative effect of repeated applications may require remedial measures, such 
as the application of aluminum sulphate to remove the excess lime. In very 
sandy soils for which so little peat is available that the plants suffer for 
nourishment the following special acid fertilizer devised for blueberries and 
eranberries will probably do well for rhododendrons, applied at the rate of an 
eighth to a fourth of a pound per square yard.” 
Pounds 
CottGnsesdimeéali_oligil .2ecl “saulclues.o LoBOb ale IU Boones 10 
aN RPM Te icEe HCI: RENO RRel fatale el omaec Neate Ruel re a eh L EN mere oe 4 
SSRI RAN Ta RN on OC AS Ie aR a Ne PE 2 
Hard water, which is alkaline in reaction, will ultimately injure an acid- 
soil planting. Rainwater or some other water that is neutral or even acid 
in reaction should be used if practicable. If only alkaline water is available 
for sprinkling purposes it can be made neutral or slightly acid by dissolving 
in it a suitable amount of aluminum sulphate. The proper amount can be 
determined by adding to a teaspoonful of the treated water in a white dish 
a fraction of a drop of the dye known as bromthymol blue. If the amount of 
aluminum sulphate added to the water was just sufficient to make it neutral, 
its color under this test will be green; if it has become acid, yellow; if it is 
still alkaline, blue. : 
Ornamental plants vary in the degree of soil acidity or alkalinity to which 
they are best adapted. The preparation of authentic lists of species on this 
8 For a more extended discussion of the decay of leaves and its relation to acid soils 
see “ The formation of leafmold,” Smithsonian Report for 1918, pp. 353 to 8438. 
®*“ Buttermilk as a fertilizer for blueberries,’ Science, yol. 64, pp. 94 to 96, July 23, 
1926. 
For a discussion of fertilizer experiments see pp. 19 and 20 of ‘ Directions for blue- 
berry culture, 1921,” Bull. 974, U. S, Department of Agriculture, 24 pp. and 29 pls. 
20837—27———26 
