Possible Independent Variables

• air movement (wind speeds, wind direction)

• atmospheric carbon dioxide (low to high concentrations)

• atmospheric humidity (low to high humidity)

• atmospheric pollution (fresh air to polluted air)

• chemical concentration (low to high concentration)

• chemicals (none vs. household chemicals)

• competition (no competition, interspecific, intraspecific)

• environment (laboratory, yard, field)

• hormone concentration (low to high)

• hormone (auxins, gibberellins, cytokinins)

• insects (presence, absence, density of insects)

• light angle (overhead, oblique, angle)

• light color (red, orange, yellow, green,  blue, violet)

• light intensity (absence or presence; high to low intensity)

• light quality (incandescent, fluorescent, natural)

• nutrient application (foliar, systemic)

• nutrients (N, P, K concentrations)

• nutrients (natural, synthetic, manufacturer)

• pesticide application (foliar, water, injection)

• pesticide concentration (low to high)

• pesticide type (insecticides, snail killers, fungicides)

• planting density (one to many per pot)

• salinity (fresh vs. saline, low to high, sodium chloride vs. other salts)

• soil bio-matter (debris from conifers, broad leaf trees, or grasses)

• soil classification (alfisols,  andisols, aridisols, entisols)

• soil pH (alkaline, neutral, acidic)

• soil profile (humus, top soil, elluviation, subsoil, regolith, bedrock)

• soil source (field, stream bank, mountain side, sediment)

• soil type (sand, clay, silt, loam)

• temperature (high to low, boiling, freezing)

• temperature treatments (duration, regimen)

• water application (foliar, basin, subsurface)

• water pH (acidic, basic, neutral, pH 0-14)

• water pollution (household chemicals, acid, base)

water source (tap, distilled, bottled, stream, lake, ocean