As you’re looking at your fertilizer bag, you see that series of numbers such as 10-10-10. The first number on the bag refers to the percentage of Nitrogen.  A 10-10-10 bag consists of 10% elemental Nitrogen. Nitrogen is one of the 3 macronutrients. The other 2 being Phosphorous and Potassium.

Nitrogen is needed in the plant to help in protein synthesis, formulation of enzymes and as a main constituent of chlorophyll. Nitrogen moves readily through the plant, so when a plant is deficient, the old leaves yellow first and will eventually drop. Shortly thereafter, new leaves will yellow. The plant also slows down in growth. So when we see a “hungry” plant, that is uniformly yellow or chlorotic, we can assume it is low in Nitrogen.

Did you know that 78% of our atmosphere is Nitrogen? Most plants, except legumes, cannot assimilate Nitrogen from the air. The three main sources of Nitrogen that plants can take up are urea, ammonia(NH4+) and nitrates(NO3-). Most ornamental plants prefer somewhat of a balance of urea or ammonium and nitrates. Too much urea or ammonia will make plants “soft” and stretchy, with extended internodes. Urea and ammonium having a positive ionic charge, will act as a cation and attach to our mostly negative charged soils with a CEC or Cation Exchange Capacity. These are taken up into the plant through active transport. Nitrates however are readily soluble in water and will not attach, as they are negatively charged anions. They will enter through a plant's root membrane as the plants are taking up water. Northern greenhouse growers like nitrates, as during cooler months their plants are still absorbing Nitrogen despite cool soil temperatures. Flowering plants in general love nitrates. Plants will have sturdier stems, great bud counts and a good leaf sheen.

Harrell’s NPK+ products are ideal for these growers. Ammonium nitrate and potassium nitrate being key constituents of these mixes. Excessive Nitrogen can induce deficiency symptoms of Potassium or Calcium. This is called nutrient antagonism. Some fertilizer ratios have Nitrogen way in excess over Potassium. This could result in problems in the future. As a general rule of thumb, try to keep your NPK ratios no higher than a 3-1-2 mix. So something like 18-6-12. Some grass type crops might be an exception to this. Foliar Nitrogen levels are often 3-4% in dry weight of the total. So when reading a foliar report, anything below 1.5% might be suspect. In a soil report, expect 35-80 ppm Nitrogen as good for control release mixes. Higher for quicker release mixes. 30 ppm or below means you are running out of fuel. Sprays of 20- 20-20 or our 9-3-6 are helpful in getting foliar Nitrogen levels up. Spray or drench either with Nitrogen levels at 200-250 ppm. Remember 1% Nitrogen on the bag is 10,000 ppm Nitrogen.

Article by Marshall Horsman and Matt Shultz