You can claim just about anything when you talk about soil amendments in Texas. That’s how we’ve ended up with crazy products on the shelves that have confusing, wild-eyed claims that their contents have “stimulating microbes” and “activating enzymes.”
I’m of the opinion that a forceful “if you claim it, you have to prove it” rule would surely be of benefit to those of us who take our gardening seriously. Now, when it comes to calling something a “fertilizer,” that statement does have to be proved — it’s a state law, and it’s clearly defined.
The end result? On one hand, we’re protected from misinformation and untruths, but we may need a little protection from ourselves because the terminology that’s used to describe fertilizers and soil amendments can be confusing, and knowing how to use them correctly isn’t an easy matter either.
Buying the best fertilizer and timing its use are critical considerations, and they demand a good understanding of a few simple facts.
Digital Access For Only $0.99
For the most comprehensive local coverage, subscribe today.
Organic or inorganic?
The purpose of this isn’t to change anyone’s way of thinking, but instead to explain how plants utilize the nutrients we supply to them. The major elements — nitrogen, phosphorus and potassium — move into plants’ roots suspended in water. Before they can do so, they must be broken down into very simple, water-soluble forms.
At the point that nitrogen, as one example, enters a plant’s roots, there is no difference in that nitrogen, whether it was produced in a factory or is the by-product of a cattle business. In that respect, organic and inorganic fertilizers are taken up by plants in exactly the same way — by osmosis in water solution.
However, there are two vital ways that the two types of fertilizers differ. Organic fertilizers dissolve (become “available”) much more slowly than inorganic types. That means they’re less likely to cause burning of foliage, but it also means that it will take them much longer to show positive results. Inorganic fertilizers, by comparison, become available for plant use fairly rapidly, so you’ll see the response more quickly.
Another big difference between organic and inorganic plant foods lies with their content percentages. The three numbers in each product’s analysis represent percentages of nitrogen, phosphorus and potassium. Adding the analysis numbers up, an organic fertilizer with a 1-2-1 mix contains 4 percent actual nutrients. Inorganic types like 12-12-12 contain 36 percent. That makes a big difference in amounts you’ll need to apply to achieve anywhere near the same results.
Soil tests tell true story
It’s important to note here tha, no matter whether you’re using organics or inorganics, you need to have your soil tested. Texas A&M has a fine soil testing lab. See http://soiltesting.tamu.edu for details and instructions. Local nurseries also offer soil tests from time to time.
When your soil test comes back, don’t be surprised if it suggests you need to apply only nitrogen — absolutely no phosphorus (middle number of the analysis) and no potassium. Phosphorus (and sometimes potassium) is almost always present in very excessive amounts in North Texas clay soils.
You probably grew up thinking that phosphorus was “for roots, flowers and fruit,” and it does promote those responses in plants, but there is already enough. Even so, I’ll admit that it feels odd to apply an all-nitrogen fertilizer around flowering and fruiting plants.
Texas A&M began use of the term “EarthKind” 18 or 20 years ago. In the case of fertilizers, it carries that “all-nitrogen” message but adds into the instructions that half or more of that nitrogen should be in an encapsulated or coated, slow-release form.
Your fertilizer will also contain minor elements, more commonly referred to as the “trace elements package.” This means it will include nutrients that are just as important but that are utilized in smaller amounts. Chief among them are iron, zinc, sulfur and others.
You may be tempted to buy a fertilizer with a weedkiller added. They are certainly credible products, and in the right places, they can do just what you want. However, they also bring a risk of causing serious harm or death to adjacent trees and shrubs, and because of literally thousands of questions I’ve been asked by anxious homeowners over the years, I will not recommend them.
To be clear: I do believe in inorganic fertilizers, and I also believe in a prudent use of herbicides. I just don’t think they should be applied at the same time.
Timing the applications
I normally encourage gardeners to fertilize in anticipation of prime spurts of growth. It takes nutrients a couple of weeks to be assimilated into the plants — and longer for organics — so you want that head start.
Whatever type of all-nitrogen (or at least, high-nitrogen) fertilizer you choose, apply it on your watering day. To minimize stripes and missed spots, put out half of the plant food while walking east-to-west and the other half while walking north-to-south.
The best times to fertilize Bermuda grass are early April, early June, early August and early October. St. Augustine has a problem with gray leaf spot in the summer, and that fungus develops most rapidly when high levels of nitrogen are maintained midseason. So, for St. Augustine, the best times to feed are early April, early June and early September.
One annual feeding in May is sufficient for buffalo grass. Early May and early September are the times to feed zoysias.
Neil Sperry publishes “Gardens Magazine” and hosts “Texas Gardening” from 8 to 10 a.m. Sunday on WBAP/820 AM. Reach him during those hours at 800-288-9227. Online: http://neilsperry.com.