Basic botany being a study of plants must include a survey of plant environments. Atmospheric conditions have pronounced effects on plants.
In fact, many plants are limited by conditions of humidity, temperature, or winds.
Gardeners soon learn which ones require wind shelter, light shade, frequent mist spraying on hot days, or maybe a shift to higher ground to avoid spring and fall frost damage.
Whether they realize it or not, these gardeners are seeking a favorable atmospheric environment for their plants.
Other Environmental Aspects Affecting A Plant
Other aspects of the environment affect a plant. One of the most important and complex environments with which a plant or gardener has to cope is the soil.
Soil As A Good Starting Point
Soils influence the plants growing in them. In turn, plants can alter the soil on which they are growing.
Gardeners should know the basic botany involved in a plant’s relationship to its soil.
A good starting point is the soil itself.
Soil is a mixture of things animal, mineral, and vegetable, of things living and dead, of liquids, solids, gasses, and in many cases, of things nutritious and poisonous.
To be more specific, most soils supporting plant life are a mixture of weathered rock particles, such as:
- Humus made of decaying organic matter
- Air
- Soil solution composed of rainwater (dissolved the soluble mineral and organic materials of the soil)
- Living organisms make the soil dynamic.
Rock Layers In The Ground
If we dig deep in our garden, sooner or later, we will come to solid rock. Now let’s work upwards.
Just above the solid rock is a stratum of crumbling rock.
This decay is probably caused by soluble chemicals leaching down through the soil.
As we move upward, these rock particles become smaller and smaller, gravelly, then sandy, then silty, and finally, we are in clay.
This comes as a surprise to most persons who have not studied soils.
We speak of sandy soils as opposed to clay soils as if these conditions had no relationship.
Technically, sand, silt, and clay are all the same thing—weathered rock, the difference being in particle size.
In millimeters (approximately four one-hundredths of an inch), the sizes are:
- Coarse sand: 2.0 to 0.2 millimeter
- Fine sand: 0.2 to 0.02 millimeter
- Silt: 0.02 to 0.002 millimeter
- Clay: less than 0.002 millimeter
So we see that sand and clay are different “grinds” of the same thing—but thereby hangs an interesting tale.
Coarse rock particles of the gravel and sand are very inert.
They dissolve at a slow rate that is insignificant; they offer no nutrients to the overall soil picture.
They are just there, contributing only to lighten the soil and cause it to drain better.
But let’s look at clay, the extremely tiny bits of rock.
Due to their small size (a chemist would say they are in the colloid range), clay particles generally carry on their surfaces an electrostatic charge.
This means that they can act like tiny magnets in their effects on each other and also on dissolved chemicals in the soil solution.
Clay particles can attract and tightly hold nitrates, phosphates, potassium compounds, and all the various other nutrients of the soil solution.
They can also have a hold on the water with varying degrees of tension.
Clay particles are, so to speak – the deposit vaults of the soil banking system.
Most soils contain mixtures of all the various mineral particle sizes.
For example, clay soil generally contains more than 30% percent clay particles.
On the other hand, sandy soil usually is made up of less than 20% percent of sand and silt size particles.
Proper Proportion Of A Good, Fertile Loam
A good gardening soil must have the proper proportion of each particle size plus balanced air, soil solution, and organic matter.
Gardeners frequently speak longingly of a “good, fertile loam.”
Here is a typical Midwestern soil sample, with percentages by volume.
- Air: 25% percent
- Mineral particles: 40% percent
- Water: 26% percent
- Organic matter: 9% percent
The mineral part may be subdivided as:
- Coarse sand: 17% percent
- Fine sand: 30% percent
- Silt: 29%
- Clay: 24%
This soil is a good “prairie” loam.
It would grow fine grasses and grain crops provided sufficient nutrients were present.
The gardener seeking to grow forest types of flowers or plants from tropical jungles would add much humus to his loam.
For rain forest species, rhododendrons, and so on, a great deal of high acid peat moss would be needed.
Soil Solution As Food For A Plant
Where does fertility fit into this picture?
The only food a plant can use is that which is in solution.
Anything a plant takes into its roots must be dissolved in the soil solution.
Nutrients are said to be organic or inorganic, but in the final step of intake by the plant, it makes little difference.
To the plant, it matters not whether its calcium intake, so necessary to the function of its enzyme systems, has come from lime water poured out as a plasterer rinses his mixing pan, from soluble limestone that has weathered naturally or from bone meal dug in by a good gardener.
The difference comes in how the chemical, in this case, calcium, is added to the soil.
Soil can be ruined structurally, or the addition of calcium can much improve it.
Soil acidity may be affected in such a way that plants may grow better or not at all.