Controlled vs. Slow Release Fertilizers: What’s the Difference & Which is best?

Controlled vs Slow Release Fertilizer

Just as our body needs a variety of nutrients to survive, so do our plants and grasses. One of such essential nutrient is fertilizer. Your turf is guaranteed to receive the nutrients to produce a green, lush, and healthy lawn when the right proportion is applied in the appropriate method.

There are two common types of fertilizers suitable for your lawn; Slow-release fertilizers (SRF) and Controlled-release fertilizers (CRF). Sometimes, both are mistaken to mean one fertilizer type. However, even they both do release plant nutrients at a slower rate than when highly-soluble conventional or ‘straight’ fertilizers are used, and they are different types of fertilizers.

They differ in the technology they require, the release method they use, longevity, factors that control the release, and more.

These differences might seem vague, but once explained, you’ll understand the distinctions between them, how each releases nutrients to your plants, and how you can operate each to achieve a lovely lawn.

Slow Release Fertilizers

Slow-release fertilizers release nutrients at a slower pace than highly-soluble traditional fertilizers. A known attribute of slow-release fertilizers is that they are not enclosed in coatings to achieve the extended discharge of nutrients.

Also, their rate and pattern of release are not controlled and influenced by other conditions such as microbial activity, pH, organic matter, and moisture, but is wholly dependent on the unpredictable climatic conditions.

A well-known method for producing slow-release fertilizers is with methylene urea generated through a manufacturing technique where long-chain molecules are created by chemically combining a nitrogen source with an aldehyde.

The primary function of the long-chain molecules is to sustain the delayed release of nitrogen by microbial action, which feeds on them gradually. The microbes gradually break down the long-chain molecules and, ultimately, the resulting ammonium nitrogen to nitrate (a form of nitrogen which plant turf can use).

With a slow-release fertilizer, the duration of release is dependent on soil microbial activity, which is motivated by soil moisture levels, growth medium, and temperature. Animal manures, composts, and ‘green manures’ enriches the soil and could also serve as slow-release fertilizers.

Still, their nutrient chemistry is complicated, and microbial activity is yet required to slowly transform the organic substances into minerals suitable for plants use.

Control Release Fertilizers

Controlled-release fertilizers are granules enclosed within carrier coatings/molecules to control nutrients release, thereby increasing nutrient supply to crops while minimizing environmental, ecological, and health risks.

They differ from Slow-release fertilizers as they are totally dependent on organic resins or polymer coatings to form prills which will regulate the rate, pattern, and duration of plant nutrient release to the soil.

The coatings function as a semi-permeable barrier to some molecules while allowing other essential particles to penetrate through. Here, the term ‘controlled’ indicates a much higher level of control in the rate, pattern, and duration of plant nutrient release than in slow-release fertilizers.

Control-release fertilizers are usually applied to an adequately-moist growth medium, with a one-way passage of water through the coatings to the inside of the compost in a process called ‘osmosis.’ The water absorbed partially dissolves the urea inside the prill to formulate a highly-concentrated solution. The urea solution is diffused into the turf.

The Association of American Plant Food Control Officials describes controlled-release fertilizers as fertilizers that contain nutrients in a way that the plant cannot immediately absorb. Uptake is delayed after application so that plants receive available nutrients for a longer time.

Distinctions between Slow- and Controlled-Release Fertilizers

At this point, you can deduce that the terms “slow-release fertilizer,” or SRF, and “controlled-release fertilizer,” or CRF, do not mean the same thing. Even when they both slowly release soluble plant nutrients at a slower rate, and for extended periods, they are not the same. The distinctions are further highlighted below;

  • Controlled-release fertilizer is acceptable for fertilizers, whose pattern and duration of nutrient release are well known and controllable during preparation and application.

Slow-release fertilizers involve a slower release rate of nutrients, but the frequency, pattern, and duration of nutrient release are not controlled because they depend on microbial organisms whose effectiveness is dependent on soil temperature and moisture conditions.

  • Controlled-release fertilizers are dependent on organic resins and polymer coatings to delay the nutrient release, while slow-release fertilizers are not enclosed in coats to achieve extended nutrient release.
  • Controlled release fertilizers last longer than slow-release fertilizers, mostly due to the coatings which define the speed with which nutrients are released.

Benefits of using Controlled and Slow Release Fertilizers

Various benefits abound when one uses either of the slower nutrients releasing fertilizers instead of quick-release ones.

  • The application of either controlled-release fertilizers or slow-release fertilizers can potentially decrease nutrient losses and fertilizer use by 20 to 30 percent of the recommended rate of a conventional fertilizer while enhancing nutrient-use efficiency.
  • With controlled-release fertilizer and slow-release fertilizer, fertilizer-associated risks are minimized, including leaf burning, water contamination, etc. The slow proportions of nutrient release can preserve nutrient concentrations in soil solution at a lower level to reduce runoff and leaching losses.
  • Eliminating frequent application of fertilizers reduces application and labor costs.
  • Another advantage of slow-release fertilizer is that the release rate is in tandem with that of the turf plants’ innate needs for nitrogen. Therefore, nitrogen is supplied to the plant at the same time they need it.

In colder weather, when the plant grows much slower, and its nitrogen demands are reduced, the amount of microbial activity also decreases, so there is no nitrogen loss to the soil.

  • The prohibition of fertilizer application in the late growth stage eliminates plant damages.
  • There is an increased amount of control over release rates, duration, and the pattern when either of the slower release fertilizers is used, and this eventually produces adequate synchronization with plants’ nitrogen demands.
  • For slow-release fertilizers, when you have enough supply of fertilizers like manure, the production cost is reduced.

Disadvantages of using Controlled release fertilizer or slow-release fertilizer.

  • Slow-release fertilizers may sometimes stand the risk of increased harmful leaching events. This situation arises as a result of their reliance on microbial digestion to stimulate nutrient availability. When satisfactory conditions for microbial activity follow after the cropping cycle, available surplus nutrients can be pollutants irrespective of the source.
  • Coated controlled-release fertilizers require more production costs than quick-release fertilizers.
  • Nutrient deficiencies may materialize if nutrients are not released as predicted due to either low temperatures, flooded/droughty soil, or weak activity of soil microbes.


Both slow release and controlled release fertilizers are considered the best type of fertilizer to use. The two kinds of fertilizers are known as the slow-release fertilizers, and each has a way of regulating the release of nutrients to extend to a lengthier period.

Although I’ve listed the advantages and disadvantages of using either fertilizer, each of them has their areas of relevance. I would recommend that if you prefer to control the rate and pattern of nutrients release and also extend the longevity of your fertilizer application, use controlled-release fertilizers.

On the other hand, if you want nutrients to release to align with the soil’s needs, and to prevent nutrition loss, use slow-release fertilizers. In all, ensure that your plants receive the vital nutrients needed in the appropriate proportion to keep them healthy and lovely.