Fertilizer Basics


January 14, 2021

It does seem like an odd time to talk about fertilizers. There’s still snow on the ground, the wind is howling, Christmas is only five days away as I write this, and you’re probably like me, not at all interested in garden or lawn care right now. On the other hand, it’s never too early to learn the basics of fertilizers so that you get the right ones for the coming season. Did you catch the word “ones”? That’s right. You’ll be using multiple fertilizers. Lawns, flowers, vegetables all have different needs. In fact, vegetables have a wide variety of needs all by themselves. The questions really is what to use and when.

Fertilizer can be either good or bad. If you apply too much, it’s bad. If it’s wrong, it’s bad, too. The right fertilizer, applied properly, is good. But how can we tell what to apply and how much? The first thing to do is find out what nutrients you need. That is…what are the nutrients your soil is lacking? The only way to be sure is through a soil test. I use CSU because it’s close and I’m familiar with their reports. Nebraska is also a good lab, but it’s further away. You’ll need to collect your own samples and the lab will provide jars specific for the purpose. Instructions come in the jars with the shipping address. If you use CSU, you can obtain collection jars from the Laramie County Horticulturalist, Catherine Wissner. Her office is located on the fourth floor of the Pathfinder Building at LCCC.

To collect your soil sample, you’ll want to dig down about 12 inches in several spots around the area you want tested. A garden spade works well, but the best method is a soil auger if you have one. Take all the soil from your holes and mix it together. Mix it well because you’re goal is to get an overall look at your garden area. They put it on newspaper and let it dry for about a week or at least until it’s no longer moist. Remix it and fill the collection jar according to the instructions. Box it up and immediately send it by priority mail to the address in the instructions. It needs to get to the lab quickly so it doesn’t have time to deteriorate and lose nutrients. If you gave an email address you’ll have a response in 2-3 weeks. The formal paperwork will come a few weeks later. One of the things I like about the reports from CSU is that they give recommendations on what to do with your soil and how to go about it.

The next critical step, before you go out and purchase fertilizer, is to know what each of your plants are going to need. Yards are fairly simple and a standard lawn fertilizer that provides the needs shown in your soil report will be sufficient. Flowers and vegetables are a different story altogether. Flowers are the easiest of the two and, generally, one fertilizer will work for them all. There will be a few variations so it’s good to do your research before planting or buying your fertilizer. Vegetables, on the other hand, have a lot of variation. For example, tomatoes and peppers are very heavy feeders and may require supplemental calcium to prevent blossom end rot. That means that you may be fertilizing them more often and with a lower Nitrogen fertilizer, especially after they start to bloom. Bulbous veggies, like onions and garlic, are heavy feeders as well. Asparagus, on the other hand, will do well on a couple of applications in the spring with a higher Nitrogen fertilizer. This is the point where I deviate from the topic and mention that a good irrigation system with isolation valves comes in real handy.

Now to fertilizer. When you go to the store to buy your fertilizer, assuming you’re buying a brand name product, ignore all the pictures and descriptions on the bag. I mean the picture of the pretty lawns or big flowers as well as the comments like “For Vegetables” or “For Roses”, etc. All you really need to look at are the two boxes that provide the analysis of the ingredients and the application requirements. All fertilizers are shown with a numerical description, three numbers. For example, 10-2-5. Those numbers represent the percentages of Nitrogen (N), Phosphorus (P), and Potassium (K) in the package. Every package of fertilizer will have this description and they will always be in the same order, even if one of the numbers is 0. In the ingredients box, on some fertilizers, you can also find the percentages of the other nutrients that are considered secondary and even micronutrients in addition to the big three primary nutrients. On specialty fertilizers, some nutrients will be missing in the product, so there may be no analysis provided for those.

Nitrogen (N) is a major player in the TV commercials and the gorgeous pictures on the packages. Although in high demand for plants, it comes with a price if applied too heavily. Nitrogen is necessary for photosynthesis and for growth in stems and foliage. It also helps set the flowers. That’s as far as it goes. Too much nitrogen will cause the plants to produce an overabundance of sugar and become sweet. With sweet comes insects. You will have a beautiful green lawn or luscious foliage, but you’ll pay for it down the road. Cut the Nitrogen back once the buds start to form.

Phosphorus (P) promotes strong and vigorous roots, stems and flowers. It is the primary building block to help the plants use the other nutrients that they need. Without phosphorus, the plant will be small with fewer and smaller flowers and fruit. You can see a phosphorus deficiency in the plant itself because it will have a very bright green or maybe even a purplish cast. A good inexpensive way to maintain an adequate level of phosphorus is to add about two inches of compost every fall and work it in well.

Potassium (K) is the nutrient that provides the big, beautiful blossoms and fruits. It helps regulate water in the plant to provide just the right amount for the plant’s needs. By regulating water use, potassium also increases the plant’s drought tolerance. For vegetables in particular, good potassium levels provide large, high quality fruits and vegetables. Potassium is easily applied in either solid or liquid form and can be applied through your irrigation system if you’re using a drip-style system. I wouldn’t advise applying through a sprinkler system. You’d just waste too much of the nutrient.

The secondary nutrients that are critical, but not to the extent of the primary nutrients, are sulphur, calcium and magnesium. Calcium and magnesium always go together since they need each other to work. These nutrients are rarely deficient in Wyoming soils, but it does happen.

All of my fertilizers are applied through the drip irrigation system for both greenhouse and soil gardening. The drip system puts the fertilizer right where it needs to be rather than just throwing it out randomly. If you have any questions, ask a Master Gardener. It’s what we do.


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