How to Fertilize Your Plants: Phosphorus and Potassium two of the Big 3 Plant Macronutrients.


The importance of phosphorus: phosphorous stimulates root formation, facilitates water and nitrogen uptake by plant roots, is required for the formation of ATP, an essential component of chromosomes, for bloom, is essential for seed formation and resistance to cold and disease.
Phosphorus sources include crushed bone and shells, but they must be broken down by microorganisms. It is mostly derived from phosphate rock that is mined and then ground up, ready for use in the garden. Phosphorus has low mobility, so sprinkling it on the surface of your garden soil is ineffective. Apply it at the time of planting or dig it into the soil, because phosphorus stays where it is applied. Unlike Nitrogen, Phosphorus is not easily leached and therefore poses no groundwater problems. Too much phosphorus can interfere with iron and calcium uptake.
Keep your phosphorus stored in a cool dry place. You don’t want it to be stinky and infested.

Symptoms of Phosphorus Deficiency

    • Plant growth is stunted
    • Leaves become darkened, and often accompanied by purple undersides and veins
    • Plants become susceptible to cold injury
    • Fruit and flower maturity is delayed

Phosphorus is a mobile element in plants, so older tissues show signs of deficiency first. Phosphorus deficiencies are common during cold temperatures. For example, if you plant your cucumbers before the last possible frost (May 24 in most of Canada), the leaves will turn yellow on top with purple undersides. Low temperatures induce phosphorus deficiencies.


Potassium is a Macronutrient in plants that is essential to several chemical processes such as activating the enzymes necessary for making protein, building macromolecules that aid sugar translocation and more. Potassium in plants helps to increase resistance to disease, making chlorophyll, builds up a plants resistance to cold and promotes the growth of larger and better quality fruit.
A deficiency of Potassium shows as a yellowing or purplish tips and margins on leaves.
Potassium, also called potash, is mined from mica and feldspar rocks.
Too much potassium can interfere with magnesium and calcium uptake.