Teague: Smart fertilizing is all in numbers, scheduling

June 13, 2014 

Keeping plants healthy and productive entails establishing a regular, consistent fertilization schedule. Fertilization replaces nutrients in the soil that are drawn up and expended or consumed by the plants.

During the peak growing seasons, the roots of plants that produce crops that are harvested or removed by deadheading from the plant (i.e., tomatoes, peaches, roses in the summer; or peas, citrus, pansies in the winter) can quickly exhaust the nutrient resources in the soil if the nutrients are not regularly replenished.

There are two important pieces of information that you should look for on fertilizer labels: the percentages of each nutrient and the recommended feeding schedule. You will find a wide variance in both.

Fertilizer labels generally display three numbers — say 10-10-10 or 5-10-5. The first number gives the percentage of nitrogen in the product; the second represents the percentage of phosphorus; the third indicates the percentage of potassium.

Choosing the right fertilizer for your plants depends on understanding the effects of these three macronutrients, especially phosphorus.

Nitrogen promotes green growth, phosphorus fosters flower production and potassium is essential for root development and vigorous health. If you're feeding a plant that produces flowers that turn into summer vegetables like tomatoes or that produces summer bouquets like roses, you'll want to choose a fertilizer with a higher middle number, like 5-10-5 or 4-6-2, that provides a higher ratio of phosphorus. If you're trying to reinvigorate the ferns that were nearly killed off by last winter's freezes, you'll want to apply a fertilizer with a higher first number, providing a higher ratio of nitrogen.

How do different percentages and different formulations with different recommended feeding schedules actually affect plants? Let's compare two popular name brands of rose and flower fertilizers (anonymously, of course).

The liquid formulation of a well-known brand lists percentages of nitrogen, phosphorus and potassium as 24-8-16 and recommends feeding roses every seven to 14 days. The lower middle number doesn't match the requirement for a higher percentage of phosphorus for good flower production.

What you will see is lots of lush green growth. (I experimented with their tomato food and had 12-foot vines with two tomatoes each). The short time between feedings indicates that the nutrients in the liquid fertilizer dissipate quickly from the soil.

The other brand, an organic granular formulation, lists percentages of 4-6-2 and recommends feeding every two months. The higher ratio of phosphorus helps ensure good crop production and the much longer period between feedings is a good indication that the nutrients are consistently available over a longer time.

Understanding the differences between products can help you maintain a healthy garden throughout our long growing seasons.


Elinor Teague is a Fresno County master gardener. Send her plant questions at etgrow@comcast.net or features@fresnobee.com ("plants" in the subject line).

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