6.4 External Factors that Affect Plant Growth

Nutrients Macronutrients: Micronutrients: Nutrients needed in amounts greater than 1% of dry weight Micronutrients: Nutrients needed in much smaller amounts Cl, Fe, B, Mn, Zn, Cu

Function of Macronutrients Nitrogen (N) Part of chlorophyll, proteins and nucleic acids Potassium (K) Controls opening/closing of stomata Calcium (Ca) Component of cell walls and membranes McGraa Hill page 597

Function of Macronutrients Magnesium (Mg) Part of chlorophyll, needed to make proteins Phosphorus (P) Part of proteins, nucleic acids and cell membranes Sulfur (S) Part of many proteins McGraa Hill page 597

pH levels Some plants thrive in acidic soil (pH 6-7): Pine, spruce, dogwood, blueberry, hydrangea, magnolia, holly, potatoes

pH levels Some plants thrive in basic soil (pH 7-8) Geraniums, petunias, lawn grass, beans, beets, lettuce, pears, plums

Light Requirements Photoperiod: the number of daylight hours Short-day plants flower and reproduce when photoperiods are shortening, example is chrysanthemum Long-day plants flower and reproduce when the photoperiods are lengthening, example spinach

Light Requirements Only 1% of radiant energy is captured by plants Chlorophyll Red and blue spectrum Carotenoids Blue green and violet spectrum