Question of the Week Number 2: March 22, 2018

“Neil, I have several types of shrubs and flowers as well as a lawn and vegetable garden. Do I need a separate fertilizer for each?”

What could my answer be that might surprise you? Well, it’s highly likely that one fertilizer is all that you really need for all of those plants. That’s unless you have some plants that are really unusual.

What’s in a fertilizer?
Any product sold in Texas as a plant food or fertilizer must disclose on its container what is called its “guaranteed analysis.” It will consist of three numbers, representing respectively the percentage content of nitrogen, phosphorus and potassium.

Photo: With this many kinds of plants, you’d assume you’d need several types of plant foods. But, no! One fertilizer, carefully chosen, can satisfy all your plants’ requirements.

What those nutrients do…
If you had a plant physiology lab, and if you could control nutrient solutions so that you could see the effects of omitting one nutrient at a time, you would see that the three macro elements (those used in largest amounts) have these effects on plant growth:

Nitrogen (N): Promotes stems and leaves.

Phosphorus (P): Promotes roots, flowers and fruit.

Potassium (K): Aids in summer and winter hardiness.

So most of us would conclude that we need to include some of each of these nutrients in our fertilizer regime.

But wait! There’s more!

Continued Below


Clay soils hold excess phosphorus for long periods of time (years). When that happens, the phosphorus has adverse effects on other nutrients, and plant growth is impeded.

Calcareous (limestone-based) soils already have ample amounts of potassium.

Therefore, he said, don’t be surprised if a soil test shows that you need to add only nitrogen, first number of the analysis.

Of course, no fertilizer will be 100 percent nutrients. There will be inert materials, or “carriers” that are included in the package to dilute the fertilizer. Without them it would be almost impossible to distribute a granular fertilizer evenly.

You want to look for a product where half or more of the nitrogen is in slow-release form. It may say that it’s “coated” or “encapsulated.” Both refer to a means of slowing the solubility of the nitrogen so that it will be “available” for uptake by the plants’ roots over a long period of time.

If any of this is unclear, ask your local Texas Certified Nursery Professional to show you what I’m talking about on the back of the bag of a product he or she has available for sale. It’s a critical lesson that, once learned, will be useful for the rest of your gardening career.

Note: The Texas A&M Soil Testing Laboratory offers complete testing of all your soil nutrient, pH and salinity issues. Here is a link for more information.

Posted by Neil Sperry
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