What To Know and Consider Before Buying Fertilizer

If you are trying to figure out which fertilizer you should buy and how much you should use, consider this. I went into a large garden center and along one wall there is a display four shelves high and maybe 20 feet long with nothing but boxes, bags, jugs and bottles of fertilizer. There were at least 80 different choices, and this didn’t even include the lawn fertilizers behind me. The choices are daunting and confusing. But it doesn’t have to be.

The very basics of fertilizers is that there are only three major nutrients in them. These are indicated on the bag, bottle or box in a ratio that looks like 5-10-5. This means that inside that container, the stuff in it is 5 percent nitrogen, or N, 10 percent phosphorus, or P, and 5 percent potassium, or K. But there’s more to it. Or is it less?

Again, keeping things on the simple side, the nitrogen is primarily used as a nutrient to promote the production of the green we see in the leaves. The phosphorus is basically responsible for the fruits and flowers, and the potassium helps with root growth and drought resistance and aids in water loss and preventing wilting.

Beyond these three elements, the label may also show a variety of what we call “trace” elements that are in much smaller quantities. Then one more step down are the micronutrients followed by the macronutrients. Keep in mind that if you’re only growing houseplants and vegetables you may only need to be concerned with the N-P-K. However, fruit, roses and other specialty crops may require more of your attention when it comes to the micro and macro subsets.

To dig a little deeper, think about a lawn. What we’re after here is green grass. We know that nitrogen is partially responsible to produce that chlorophyll that makes the grass green so you should expect that a lawn fertilizer will have a good deal of nitrogen. For plants that we want to primarily get flowers from, we turn to phosphorus so the middle number will be higher in those fertilizers. So you can see why 10-0-4 would be a good lawn fertilizer while 5-10-5 would be good for geraniums, petunias and perennials.

Another thing to consider is the value in the fertilizer you buy. Let’s use a one-quart bottle of Tiger Bloom 2-8-4 as an example. You can tell from the analysis (2-8-4) that this fertilizer is intended for blooming plants because it’s got a high amount of phosphorus. At the same time, note that this 1-quart bottle costs $35 for the 32 ounces (1 quart) of product. Is this a good value?

To figure this out we have to determine how much of the contents is actually fertilizer and how much that fertilizer costs. To do this, add up the percentages of N-P-K, and in this case it comes to 14 percent. This means that 86 percent of what’s in that bottle isn’t fertilizer and just a liquid carrier. Doing the math, this reveals that the fertilizer is only worth $4.90 while you’re paying $30 for water or some similar carrier. Now, is that a good value?

On the other hand, there is the bottle of Neptune 2-4-1. This one comes in a 32-ounce bottle for $23. This means that 7 percent of what’s in the bottle is fertilizer. Doing the math we find that the fertilizer in this bottle is worth $2.24 while the carrier is costing $20.76. If you’re good with math you can do your own extrapolations to figure out the true cost of the N, P and K using the percentages in the N-P-K notation.

Now one other little tidbit that you may want to add to the confusing equation. The Tiger Bloom is not organic while the fish emulsion is. To many gardeners, this is an important consideration, and you should also look at the application rates as these may come into play as well. Can you make the organic fish emulsion into 4-8-2 and a bit closer to the Tiger Bloom ? Yes, all you have to do is double the application rate, but this also makes the fertilizer more expensive as it will only go half as far.

If cost isn’t your driving factor, there are other things to consider when you choose fertilizers, and here, we get into the age-old debate of organic vs. chemical and what we refer to as the method of delivery.

Over the years as I’ve come to better understand soils and soil chemistry, I’ve moved farther and farther away from chemical fertilizers. Simply put, they are not good for the environment in terms of their ability to pollute, but they also are quite harmful to soil microorganisms. Soil microorganisms are critical for good soil health and in soils where chemical fertilizers are used, they tend to become scarce or absent. Chemical fertilizers also have the ability to burn roots when they are improperly used and applied.

Organic fertilizers, on the other hand, tend to be soil builders that encourage and promote soil microorganisms. Yes, organic fertilizers will undoubtedly be more expensive then the chemical types, but remember that the organics are naturally time released and require less frequent application. Many contain mycorrhizal fungi, which are also a great benefit when it comes to soil building and soil health.

The next consideration is how the fertilizer is applied. Here I don’t mean do you apply it with a hose, a spreader, in rows or rings but what the physical characteristic of the fertilizer is. Obviously you know there are liquid fertilizers but when you get to solids there are many choices. Lawns rarely get fed with liquids, and here we mostly use granular or pelletized fertilizers. There are some granulars that are treated to be time released, but many of the long-lasting lawn fertilizers are encapsulated in a plastic-like material that breaks down slowly in the presence of water and warmth. These are much safer than, say, a bag of straight chemical 10-0-4, but much more expensive. The chemical 10-0-4 can also burn roots when it gets hot and humid, but the time-released fertilizer usually won’t do this.

Fruit trees are usually fertilized using banding, soil injection, holes filled with fertilizer (rare used these days) or tree spikes. If your fruit trees have large mulch rings or other non-lawn materials out to the drip line then you can find instructions on what fertilizer to use as you ring it around the tree at the drip line. Most gardeners with more than just a few fruit trees may use a soil injection method where a needle is inserted into the ground and fertilizer mixed with water is injected into the soil. The last method is using fertilizer spikes inserted as per the instructions, and these spikes release the nutrients over several weeks.

When considering which type of fertilizer to use, consider this: For a few cents you can mix the miracle product (a pure chemical fertilizer) with water and use it on your tomato plant. It acts like speed or amphetamine and gives the plant a quick shot of nutrients that may last a day or two. However, instead you could add an appropriate amount of an organic fertilizer in a ring around a similar tomato plant, work it into the top of the soil and water it in. That single dose of organic fertilizer may cost many times the cost of the chemical fertilizer, but it lasts and works days and even weeks longer than the miracle stuff. Food for thought. Nutrients, organic ones, for your plants.

For those who want to add fertilizer but don’t want to have to do it repeatedly during the year or growing season, you can use a product like Osmocote, which is time-released prill. In the presence of soil moisture it releases the nutrients over time. It’s available in several formulations depending on the type of plant you’ll use it on and the length of time you want it to last. It’s convenient but not cheap and not organic.

Products like Osmocote are great for use in planters and pots where you mix it in with the soil at the initial planting and you’re done. In very wet and warm summers though you may find the need for a supplemental application of a different fertilizer later in the season once the Osmocote leaches out.

If you use a product like Osmocote keep in mind that the plastic “prill” that contains the fertilizer may not degrade and can still show up in the soil even when the fertilizer is depleted. Let the time length on the label (as in three months etc.) be your guide and not the presence of the plastic casing.

As mentioned, I’ve pretty much turned away from chemical fertilizers. This means I need to keep better track of what I fertilize and when as multiple applications during the growing season are usually necessary. A mindful gardener learns how to read the leaves and flowers of a plant and or its fruit production to know when more fertilizer is needed.

Years ago, applying fertilizer to the foliage — foliar feeding — of some flowering plants and fruit trees was a common practice. However, research has shown that except in a few particular situations where there are trace element deficiencies, this method of adding nutrients is generally ineffective.

If you need a very basic primer on fertilizers, the North Carolina Cooperative Extension had a nice one here: tinyurl.com/4uzaacjc. Keep in mind that any dates and timing issues need to be adjusted for out here. And for those of you who limit nutrients to organics, remember that soil microorganisms that break down organics become most active when soil temperatures reach 50 degrees. Added nutrients to colder soil can result in the leaching of the unused material both in early spring and late fall.

I find that my roses need feeding about every two weeks once the soil warms up. The same with the few vegetables I grow, but my greens need very little other than a small amount worked into the soil at planting. The perennials get one feeding after the soil temperature reaches 50 degrees (at night) and my lawn gets an organic fertilizer once in May and again in late September. I bought a 1-pound jar of Miracle-Gro, a pure chemical, and very fast acting fertilizer about 10 years ago. For this convert, it’s still in the jar. Keep growing.