Am I Applying Too Much Nitrogen?

Q. We fertilize all of our bushes early spring and mid fall with a 5-10-5 liquid plant tonic.  Hopefully this isn't too much nitrogen.

This concentrated fertilizer
 has no nitrogen but very
high percentages of phosphorus
and potassium

A. There are two ways to look at this question. Applying too much nitrogen can mean either applying it too often or applying too much in a single application. If you follow label directions, the amount of nitrogen applied should be correct. Apply nitrogen as often as 8 weeks apart if you want continuous growth.

             Applying excessive amounts of nitrogen can damage plants or cause excessive growth of leaves and stems.

            When judging how much fertilizer to apply and how often, observe the plant. If the plant does not have good growth or the flower size and numbers have diminished, apply fertilizers or “plant tonics” if you prefer.

Applying too much nitrogen, the first number, is not normally a long-term problem. The potential long-term problem involves the over application of the second or middle number, phosphorus. 

Phosphorus stays bound in many soils for much longer periods of time than nitrogen. Apply fertilizers containing high levels of phosphorus (middle number) less often than fertilizers that contain high levels of nitrogen.

As a general rule of thumb, apply fertilizers containing phosphorus once a year to established plants, two weeks before flowering. The rest of the time use high nitrogen fertilizers.

The exception is at planting time. Every time seed or transplants go in the ground, apply a high phosphorus fertilizer. Before planting, mix high phosphorus fertilizers in the soil to the same depth the roots will grow.

Bagged compost can be hard to find. Most
bagged products that contain compost are
soil mixes, not straight compost.

Consider using compost instead of a mineral fertilizer. I am talking about compost which is harder to find, not a soil mix that contains compost. Most composts have a good balance of nitrogen, phosphorus and potassium and can be used as a substitute for mineral fertilizers.

Composts provide plants with a lot of minor elements not found in mineral fertilizers. Compost lowers soil alkalinity, stimulates good soil microorganisms and provides humus or “black gold” to the soil. It is a very powerful addition to desert soils.