Basic Requirements of Plant Life 
I N THIS SHORT GUIDE it is taken for granted that most trees and shrubs require the same things—as to 
food, air and water. Only exceptions are noted. Thus a plant needing more air than usual at its roots is 
marked “loose soil” or “drain”. Plants very easy to grow are referred to as “tolerant”. Normal plants may 
have no notes whatsoever. 
THE LEAVES NEED:— 
1. Air—“wind”, “city air”. 
Carbon is absorbed from air. 
Ordinarily the gardener has no 
worries about the leaves getting 
air. Some plants, like Tsuga, 
burn in strong winds. Bad city 
air is harmful to some trees. 
2. Light—“sun”, “shade”. 
Light makes the chlorophyl fac¬ 
tory turn its wheels. All plants 
need some. Even dense shade 
has some light. Those that get 
along best on little light are 
marked “shade” in this Guide. 
Those that need a great deal 
are marked “sun”. — Normal 
plants are not marked — they 
live in sun or part shade. 
3. Heat—“Zone I” to Zone VI”. 
There is a northern limit for 
every plant, beyond which it 
cannot live. For practical use 
the map at the right divides 
the country into Zones. Each 
plant description in this Guide 
has a related Zone limit (e.g., 
Abies Balsamea, page 11, it is 
Zone II). Look up your garden 
on the map and you can select 
hardy material. (The system is 
not perfect and local conditions 
effect changes.) 
THE ROOTS NEED:— 
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1. Air—“loose”, “heavy”, “drain”. 
Roots get oxygen from air that filters 
into the earth. Some plants need 
more than others. These must have 
loose soil in which the air is purer 
and will suffocate in heavy damp 
clays. Magnolias like heavy soil, but 
it must be drained from beneath or by 
the slope of the land. 
2. Water—“damp”, “dry”. 
Roots can only use chemicals that 
are dissolved in water. Also, water is 
the means of transportation up the 
stem. Some plants need more than 
others and die in severe droughts. In 
the descriptions (pages 11 to 37) such 
plants are marked “damp”. A loose 
soil quickly dries, a heavy soil keeps 
damp. Thus water and air for the 
roots are both present in a mixed soil. 
Normal plants that thrive in this 
“ordinary garden soil” need no nota¬ 
tion. Rainfall and drainage are com¬ 
bined in water and air supply. 
3. Food “humus”, “rich”, “barren”. 
a. Potassium—most soils have plenty. 
b. Phosphorus—needs to be added in 
most soils with fertilizer. 
c. Nitrogen — cannot be used until 
turned to nitrate. Fertilizer sup¬ 
plies it, but water quickly leaches 
it out, so the plant depends on bac¬ 
teria in the soil. These bacteria 
depend on:— 
1. Acidity of soil (lime, etc.) 
2. Drainage of soil (air). 
3. Humus in the soil (food). 
d. Iron, Lime, etc. in small quanti¬ 
ties usually present anywhere. 
Basic Facts 
First, the backbone of the soil is broken 
rock. Clay is finely powdered, sand 
coarsely broken. 
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Sand lets water run away at once, hence 
is full of air, but dry. Clay almost pro¬ 
hibits air, tho’ damp. A mixture (most 
soils) permits a balance between air and 
water. In this balanced condition soil 
bacteria can thrive. From this soil, 
water dissolves food (salts). 
Second, decayed organic matter, “humus”, 
“peat-moss”, “peat”, “leaf-mold”, etc., 
requires bacteria to break it down into 
decay. From this decay the soil-water 
About Soils 
dissolves food for roots. Also each par¬ 
ticle of humus acts as a little sponge, 
holding the water, yet permitting air 
around it. Some humus of some sort is 
present in most soils, any soil can be 
improved by some increase in humus. 
Manure combines humus and fertilizer. 
Third, nitrogen is useless to a plant until 
turned into nitrate. To provide this by 
fertilizers, means applying it after every 
heavy rain. Nature does it with soil 
bacteria. 
THE SOIL BACTERIA 
Plants use chemicals only after trans¬ 
formed by bacteria. “Top-soil” is a word 
which we give to soils filled with this life. 
Burning it over, kills them. Too heavy a 
dose of fresh manure chokes them. 
1. Their prime purpose is to provide 
nitrates. Phosphate helps this work. 
Some lime helps also. 
2. Bacteria promote decay, thus provide 
long-term food supply. Lime hastens 
this decay process. Bacteria are fussy 
about soil acidity. Most need “lime” 
reaction. Rhododendrons, etc., grow 
among bacteria which need acid soil. 
(The word “acid” in plant descrip¬ 
tions connotes this.) 
4 
