It’s here. We can start planting vegetables, annuals, perennials, trees, and shrubs. For many of us, that is the fun part, but it also means caring for those plants becomes a summer-long responsibility. You probably have the light and water requirements memorized and know about weeds popping up after every rain. However, fertilizers can be confusing. There are just so many of them, and they seem to use a code that needs to be deciphered. Perhaps the following will help.
Before getting to the letter codes, we must understand the differing methods of fertilizing, organic or conventional. Organic fertilizer works more slowly because it functions by promoting a healthy soil in which roots can take up nutrients. It will not burn plants if you accidentally use too much. Conventional fertilizer works as soon as it is applied because it is readily available to roots, however there is a danger of “burning” the plants if too much is used. They both come in granular and water-soluble types. Which type you choose depends on how you garden. It is also okay to use one type on certain plants and another on the rest of your yard.
The next thing to consider is whether the fertilizer is slow-release or fast-acting. Usually, slow release will be in granular form, and fast will be water soluble. In-ground beds respond well to slow-release because it is spread once in spring, when it is easy to see where it lands. You want it on the soil, not on the plant itself. Water-soluble is good for containers, but slow-release also works fine.
All-purpose fertilizer will have the letters N, P, K on the package, the three most needed elements in plants. N stands for nitrogen, which promotes healthy green foliage. This number may be higher than the other two, especially if using it on annuals and perennials. P stands for phosphorus, which contributes to strong roots and blooms. The number corresponding to P on the package will be higher for bulbs, corms, and tubers in fertilizer for those plants. K means potassium, and it promotes healthy plant growth.
A balanced fertilizer will have equal amounts of N, P, K, such as 10-10-10 or 12-12-12. If the fertilizer is for a specific type of plant, it is no longer balanced. For example, an organic bulb fertilizer might say 3-5-3.
Plants also need some micronutrients, but you rarely need to worry about those unless a soil test says you are deficient in one.
Annuals require more fertilizer than perennials because most of them bloom all summer and have multiple flowers per stem. Perennials bloom at a specific time and then usually not again until next year. They use less energy and require less fertilizer.
If you need help understanding fertilizer or any other gardening problem, call the Edgar County Extension Master Gardeners at 217-465-8585 or email schiver@illinois.edu.
Illinois Extension leads public outreach for University of Illinois by translating research into action plans that allow Illinois families, businesses, and community leaders to solve problems, make informed decisions, and adapt to changes and opportunities. Illinois Extension is part of the University of Illinois Urbana-Champaign College of Agricultural, Consumer and Environmental Sciences.