Both chemical and organic fertilizers are made up of macronutrients as well as micronutrients.
Macronutrients are those nutrients needed in large amounts and the presence or absence of any one macronutrient can have a detrimental effect on plant growth. See A Guide to Determine Nutrient Deficiency’s in Plants.
Three macronutrients – nitrogen (N), phosphorous (P) and potassium (K) – are essential for all plant growth. All fertilizer labels show the ratio of these three primary macronutrients. For example, 2:3:2 (14) represents the ratio of N:P:K, with 14% available plant food and the remainder being carrier constituents. Nitrogen is essential to maintain healthy, green, leaf growth, phosphorous is required for good root development, while potassium encourages flower and fruit formation. Secondary macronutrients are magnesium (Mg), calcium (Ca) and sulphur (S).
Micronutrients are trace elements that are needed, in minute quantities, to act as growth regulators in building chemical compounds in plant cells. See A Guide to Determine Signs of Nutrient Deficiency’s.
Micronutrients are iron (Fe), zinc (Zn), manganese (Mn), boron (B), molybdenum (Mo), and copper (Cu). These are usually included in plant food formulations such as Nitrosol, African Violet Food, Seagro, Supranure Plus, Multi-feed P, Kelpak and Trellmix.
Plant foods are highly concentrated and should be used with care. Follow directions for diluting them with water before application. Although they are usually indicated for pot plants, they can be beneficial for all plants.
Slow–release (SR) nitrogen fertilizers release nitrogen over a longer period, eliminating the risk of burning the plant with too much nitrogen and making it possible to fertilize fewer times in a season.
Nitrogen in a highly acceptable form is released by biological action, as and when the plant needs it. Slow–release nitrogen has made fertilizers more user-friendly. Examples are 3:2:1 (28) SR for lawns and general fertilizing of shrubs, trees and climbers; 3:1:5 (26) SR for roses, fruit trees, flowers and vegetables. Grostix Foliage 5:1:5 (22) for pot plants; and Supra 4:1:1 (18) for ferns and palms.
Any chemical fertilizer that does not contain slow–release (SR) nitrogen needs to be watered well after application to prevent plants from suffering chemical burn.