What you're learning
Slow-release fertilizers release a small, steady amount of nutrients absorbed by the soil over the course of time. This is made possible by the technology of coated pellets or prills that releases nutrients into the soil in intervals.
The release rates depend on the amount of time, soil temperature, and soil moisture, as well as pH. For the most part, soil temperature dictates how much nutrients get released as well as microbial activity.
In contrast, quick-release fertilizers such as ammonium nitrate or urea and ammonium phosphate, although are cheaper, may be more harmful to soil quality and the environment.
Most quick-release fertilizers come in liquid and granular forms and are water-soluble supplying the nutrients immediately. Excess fertilizer washes off lawns and gardens with water and drains into nearby water bodies. Excess nutrients deplete oxygen in water affecting aquatic life and affect overall water quality.
Types of slow-release fertilizers
It can be quite overwhelming to shop for a fertilizer with the various choices available. The types are also quite confusing but mainly fall into two types:
Organic and Soluble
There are organic environmentally friendly slow-release fertilizers made from plant, animal, and mineral ingredients. The release rates are dependent on microbial activity which is triggered by a moist and warm environment.
Coated Slow-release Fertilizer
This type controls the release and interaction of the fertilizer and soil by physical means like coating. This type accounts for about 95% of slow-release fertilizers. The release rates also depend on moisture and warmth and could take up to 12 months.
What is a good slow-release fertilizer?
Choosing the right slow-release fertilizer for your plants should primarily address what the plants need. The effectivity depends on supplying the nutrients at the right time, at the right rate, and place for the crop.
Similar to quick-release fertilizers, slow-release fertilizers have N-P-K ratios. Each number represents a percentage of each essential nutrient making up the fertilizer. Each element has its specific purpose:
- Nitrogen aids in plant growth and healthy leaf coloring
- Phosphorus is important in root development and the production of seeds, flowers, and fruits
- Potassium keeps the stems nice and strong and supports the overall growth
Before adding fertilizers to your garden or plants, consider doing a soil test to see what specific nutrients it needs. You can purchase a soil test kit and do a quick test or send off samples to a local agricultural laboratory.
How do you use slow-release fertilizer?
For indoor houseplants
For indoor plants, you might want a fertilizer that has higher nitrogen and less phosphorus content. This ensures you have healthy green foliage growing all year long.
Fertilize during the spring and summer where active growth is expected. Notice how fast your plants are growing and complement with fertilizer use. The frequency of fertilization would vary from every week for heavy feathers to every few weeks for non-heavy feeders. Yellowing leaves may be a sign of nutrient deficiency.
In fall and winter or during dormant periods, dilute the fertilizer to half its potency.
For the vegetable garden
Trees, shrubs, and perennials would benefit from 14-14-14 slow-release fertilizers. Consider a higher phosphorus content for flowering or fruit-bearing plants that are heavy feeders.
Note that herbs grow better with less fertilizer and should only be fed half the recommended amount.
For the lawn
If it is more for general use like lawns, you can consider using fertilizers with a relatively higher nitrogen ratio. Look for turf fertilizers, that have at least 25% or more nitrogen in slow release form. Note that nitrogen is very mobile and so the amount to maintain the turf varies for different lawns.
If available, choose fertilizers combined with herbicides for common lawn weeds to save you a bit of time.
It is best to fertilize just before expected grass growth periods and will vary from one area to another. It is also ideal to set up a regular schedule for fertilizing your lawn.
One thing to keep in mind is that in the warmer season, the nutrients in slow-release fertilizers are released at a higher rate. So spread the fertilizer in spring or summer or right before the growing period.
Read product labels carefully and safely handle fertilizers by using gloves and limiting your hand’s exposure to them. Also, store all plant food in a cool, dry place.