TM 5-803-13/AFM 126-8
(a) Lime. The addition of lime to the soil
Local agencies such as the State Agricultural Experiment
Station, County Extension agents, Soil and Water
reduces acidity. Many woody plants are somewhat
Conservation District, state university or qualified private
tolerant of soil acidity and require no pH adjustment.
organizations may be contacted for information about
However, some ornamental plants may require that an
laboratory soil tests. The laboratory test report will
alkaline soil condition be maintained. Advice on correct
include specific recommendations on materials required
amounts and times for liming can be obtained from a
to bring the soil to acceptable levels of acidity (pH) and
reliable local nursery or County Extension agent.
(b) Sulfur. If soil tests reveal that the soil is too
organic content.
alkaline, it is generally good practice to add sulfur in the
b. Additives. Various materials may be needed to
form of commercially available, acid-producing com-
improve substandard soil, but precautions should be
pounds. Aluminum sulfate is the most readily available
taken in their use.
source of sulfur. Again, as with lime, advice should be
(1) Soil conditioners. The addition of soil condi-
sought concerning the quantity of chemicals which should
tioners improves the friability and, except for sand, the
be added to achieve the desired pH.
moisture-retaining capacity of the soil. Humus (peat),
(3) Fertilizers. The use of fast-acting fertilizers in
spent manure, sand and commercially available minerals
the soil mixture at planting time is of little value since
such as vermiculite and perlite can be mixed with plant-
plants are not able to use plant food effectively until they
ing soil. As a general rule, a mixture of one part sand or
become established. Highly soluble plant food may leach
mineral soil conditioner, one part humus and one part
away before the plants have recovered sufficiently to use
topsoil will provide a Soil mixture suitable for planting
it. In fact, the use of fast-acting fertilizer in the soil at
trees and shrubs.
planting time may actually burn or damage plants. It is
(a) Sand and minerals. Coarse sand and
more effective and safer to use slow-release fertilizer
minerals such as vermiculite and perlite are especially
pellets in the soil or to top-dress plant pits and beds with
useful for making heavy clay soils more friable. Since
a moderate amount of fertilizer at the time of planting.
none of these soil conditioners contain plant nutrients,
(4) Soil wetting agent. The addition of a commer-
they should be supplemented with fertilizer. Sand is
cially manufactured soil wetting agent increases the
usually the most readily available and inexpensive
ability of heavy clay soils to absorb water. Such an agent
material, but is much heavier than mineral conditioners.
is especially useful in large plant containers for increased
Vermiculite and perlite are light in weight and should be
moisture penetration prior to transplanting. Although the
used for planter boxes or roof gardens where structural
cost may be justified in limited areas such as planter
load is a significant consideration.
boxes, these wetting agents are not recommended for
(b) Humus. Humus, in the form of peat moss, rot-
large scale use. Wetting agents may be applied as an
ted sawdust or spent manure, can be added to the soil to
additive dissolved in water or in granular form as part of
provide organic matter and promote healthy plant growth.
the planting soil mixture.
If peat is not readily available, any decomposed vegetable
compost can be used. If the cost of adding commercial
humus (peat) to the soil is too high, acceptable results
surrounding them remain saturated, because roots cannot
often can be obtained by use of more economical and
absorb oxygen and the plants will suffocate. Excess soil
locally available sources of organic material.
water becomes stagnant and the roots of newly set plants
(2) PH adjusters. The need for pH adjusters may
often rot. Surface or subsurface drainage must be
be indicated by the laboratory test report and recom-
provided to collect and carry away excess water since
mendations. The pH scale for most soils ranges from 4.0
most plant species are not capable of enduring prolonged
(strongly acid) to 10.0 (strongly alkaline) with 7.0 being
periods under wet soil conditions. Some plants, such as
neutral. Most plants absorb nutrients best from soils
willows, grow better under these circumstances, but they
between pH 6.0 to pH 6.5, whereas lawn grasses thrive at
are few in number. Newly set plants are more susceptible
pH 6.5 to pH 7.0. Ericaceous plants are acid-loving and
to suffocation from excess water than well-established
prefer soil which tests at about 6.0. If available soil varies
plants. Collection of excess water may be accomplished
radically from acceptable levels of acidity or alkalinity,
by either of the methods described below.
pH adjusters can be used. Correct measurement and
a. Surface drainage. Surface drainage in swales or
thorough mixing are essential when adding these
ditches is the most common means of collecting water
materials. Too much acidity in the soil is as harmful to
and providing positive drainage. This method is more
plants as too much alkalinity, even for such ericaceous,
economical than subsurface systems. When drainage
broad-leaved evergreens as azaleas and rhododendrons.
swales or ditches must be crossed by pedestrian or
Lime and sulfur are the most commonly used pH
automobile traffic, it is better to provide subsurface sys-
adjusters.
tems. Swales and ditches are difficult to maintain if banks
3-3
Previous Page
