What to know about fertilizer and how to use it
As we look forward to spring and getting out to work in the landscape, one of the tools for success includes the use of fertilizers.
However, like any tool, it needs to be used properly.
Most of the nutrition that a plant needs comes from the soil itself. However, there are times, especially when the native soil has been scraped off, compacted, or topped with fill, that fertilizers are needed.
Here are some answers to some basic fertilizer questions that are intended to help in figuring out how to use fertilizers better, while creating a sustainable healthy landscape.
What is fertilizer?
There are 17 nutrients that are essential for plants to grow and thrive. They are grouped into macro-nutrients and micro-nutrients.
Macro-nutrients are those nutrients that plants use in larger amounts. They include nitrogen, potassium, phosphorus and magnesium.
Micro-nutrients, while just as critical, are needed by the plants in smaller amounts. They include boron, manganese, and zinc. Fertilizers are blends or mixtures of these elements that can be applied to provide for the plant’s needs, especially in the case of a nutrient deficiency.
How do plants take up fertilizer?
This is one of the most interesting things to me about how plants work. The nutrients are held in place by the soil particles.
Organic matter and clay particles hold onto these nutrients a lot better than sand particles. In order to be taken up by roots, the nutrients must be in a form that can be dissolved in the water that surrounds the soil particle.
Why fertilize?
We apply fertilizer to supply the nutrients to improve plant growth or correct a nutrient deficiency.
What about pH?
The pH of the soil is a measurement of the acidity, or alkalinity, of a soil. The key is maintaining a soil pH where most nutrients are made available to plants.
That pH range is typically 5.8-6.5. A perfectly neutral pH is 7.0 which means most plants prefer a slightly acidic soil pH. It is important because at low pH (acidic soil) and high pH (alkaline soils), some nutrients are excessively available to plants (toxicity) while others are in a form that makes them unavailable (deficiency) to plants.
With soil pH affecting the availability of nutrients to plants, it is recommended that folks get their soil pH tested first. Getting the soil pH figured out often corrects nutrient deficiencies without having to apply any fertilizer at all. For a lot more information on soil pH go to: edis.ifas.ufl.edu/publication/SS480.
Are there different types of fertilizers?
Yes, a walk down the fertilizer aisle can be very daunting when trying to figure out what is best for your needs.
Organic fertilizers are materials that come from living things, or once living things. They include manure, compost, and plant residues. They typically release nutrients more slowly as they are broken down by soil microbes.
Inorganic fertilizers are mined from the ground or synthesized from non-living materials. Most inorganic fertilizers are readily available to plants unless they are treated in a way that makes them release nutrients more slowly.
Quick-release fertilizers are typically inorganic fertilizers that are easily dissolved in the soil solution and are easily available to the plant. The downside is that they are also easily washed further down into the soil away from plant roots.
Slow-release fertilizers (or controlled release) release nutrients over a longer time. They can be organic, or inorganic fertilizers treated to be slow-release. Polymer, or sulfur coatings, are examples of slow-release treatments. The benefit of slow-release fertilizers is that nutrients are available to the plant longer and are less likely to be washed away from the plant.
How to figure out what is in fertilizer: There is a box on all fertilizer labels called the “Guaranteed Analysis”. This box will contain all the information on what nutrients as well as the amounts are in the fertilizer as well as if they are quick release, or slow release.
You can tell a lot about the quality of the fertilizer by looking at the guaranteed analysis.
What is the proper time to fertilize?
This is easy. Don’t fertilize when the plant is not growing. A good example is in the winter. If it is not growing, it is not taking up nutrients. Any fertilizer applied will be wasted.
Can you fertilize too much?
Yes, applying more of a nutrient than the plant can use can create a nutrient toxicity. This is easy to do with micronutrients. Some nutrient toxicities can cause plant decline or even death.
How do you fertilize potted plants?
Potted plants don’t need as much fertilizer because the root system is constricted to the size of the container. An all-purpose water-soluble fertilizer is usually the best option. Some are even formulated specifically for plants in containers. Read and follow the label on the fertilizer for timing and amount. Less is usually better. Occasionally flush out the fertilizer with additional water to prevent fertilizer buildup.
While this article might have been full of details, the key points are don’t provide more fertilizer than the plant can use and use quick release/ slow release based on the needs of the plant. With this information, you can navigate the fertilizer aisles with confidence. For more information from the University of Florida go to edis.ifas.ufl.edu/publication/MG448.