Slow Release Fertilizer: How To Use Them In The Garden

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When you compare controlled or slow release fertilizer to other commercial fertilizers, you will find that they are very convenient and provide predictable results.

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Still, you may wonder whether these products like Osmocote fertilizer can provide complete nutrition for your plants. 

Should you combine slow and controlled-release fertilizers with other soil supplements? Which types are best?

In this article, we will explore the qualities of slow-release fertilizers in comparison with other types and provide advice and guidance to help you make the best choices to suit your needs. Read on to learn more.

How To Choose Slow Release Fertilizer – Choose Carefully

When you shop for garden fertilizer, you may find the endless choices quite baffling.

There are so many different kinds of fertilizers – from quick releasing fertilizers, granules to powders to liquid fertilizers – and they all claim to be the best. How can you choose?

One thing you should always keep in mind when selecting commercial fertilizer products is that slow and controlled-release products like these are almost always preferable to quick-boost liquid plant foods.

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Photo Credit: Instagram @therootculturist

It may seem that products that offer a large boost of nutrients all at once would be preferable, but the fact is these types of products can be very harmful to your plants and do nothing to improve your soil.

Fertilizers labeled as time or slow release fertilizer provide plant nutrients more naturally, depending on interaction with natural organisms in your garden soil.

Controlled slow release fertilizer products (aka: coated) are a little bit different. They release nutrients in a specific and controlled manner regardless of fauna in the soil. Either way, the gradual delivery of nutrients is preferable to a sudden overdose.

Plants Need To Eat Regularly

No single fertilizer will meet all gardening needs, but if you want to choose one primary product – a complete fertilizer – to use on a regular basis, a controlled or slow-release fertilizer product is your best bet.

NOTE: Examples of a complete fertilizer 14-14-14 or Triple 14 fertilizer,

With these products, your different plants will not go through periods of intensive nutrition followed by starvation. This sort of feeding is just as bad for plants as it is for any other living being.

When plants’ roots are swamped in nutrients all at once, and then these nutrients are depleted and/or washed away, it goes without saying crops will suffer and may die. 

With controlled or slow-release formulas, your plants, including trees, shrubs, annuals, turf grasses, and perennials, can expect regular time-release feeding every day. Naturally, this provides for better overall health.

This type of plant feeding is also better for the environment. When nutrients are released in a measured manner, they have less chance of running off into waterways. 

Excessive fertilizer runoff is a big environmental problem and one that we would all do well to avoid.

How Are Fertilizer Release Rates Determined?

Most of the time, soil temperatures and soil moisture play a big part in the rate at which the nutrients are released. There are two reasons for this.

  • Soil temperature affects the rate at which nutrients diffuse over slow release fertilizer coating.
  • Temperature influences the microbial activity in the soil.

The Best Time Release Fertilizer Products Offer A Less Costly Alternative

Time release fertilizers provide very precise results; however, they can be a bit costly. Slow-release fertilizer formulas can provide a slightly more affordable alternative. There are currently two types of time-release fertilizers on the market.

1. Synthetic Organic Slow-Release Nitrogen Fertilizer: When fertilizer shopping, you are sure to run across quite a few that are labeled as combinations of formaldehyde, nitrogen, and urea. If you see the labels:

  • Urea Formaldehyde
  • Methylene Urea

…you will know that this is a “synthetic organic” product. These products are typically made using as much as 70% WIN or water-insoluble nitrogen.

The rate at which these products release nutrients is determined in large part by bacterial activity and not by temperature or availability of water. 

The longevity of these types of products varies from manufacturer to manufacturer, but the best ones can provide nutrition for a number of weeks or even months.

There is also a product known as IBDU or isobutylidene-diurea. This type of product is 90% WIN. The release of nutrients from this product is mostly controlled by soil moisture and pH levels. Conduct a soil test to determine the acidity and structure.

Another variable that determines the speed with which nutrients are released is particle size. If the fertilizer product is made up of small particles, the nutrients will be released more quickly.


2. Natural Organics: The soil improving abilities of natural, organic soil amendments make them a popular choice among home gardeners. There are many different kinds of organic fertilizers, and they release nutrients at various speeds. Determining factors include:

  • Temperature
  • Fungi in the soil
  • Bacteria in the soil

When the soil is very active biologically, nutrients are more readily available.

Natural organics come in a number of different mediums. Among them are:

All are good choices. The more you learn about gardening and fertilizers, the better able you will be to select just the right organic matter to suit your needs.

Different Choices In Slow-Release Fertilizers

At present, there are three main types of slow release fertilizers available for home gardening. They vary in price, but all are rather costly when compared with fast release products.

Nonetheless, the fact that the application is less frequent and less time-consuming can certainly help you make up for the cost difference.

Plant soil with green fertilizer pellets.Pin
Photo Credit: Instagram @perfectplantsnursery

This slow-release fertilizer type is generally superior to fast-release products or quick-release forms, and that is why it is usually chosen for use in nurseries. 

As a home gardener, you will do well to choose high-quality slow-release fertilizers to establish your new plants because they are probably already accustomed to it.

Are Slow-Release Fertilizer Products Preferable To Natural, Organic Fertilizers?

Time release fertilizers are more predictable and more concentrated than natural, organic slow-release fertilizers. They are a little bit easier to use and are less expensive in the long term.

Additionally, they take quite a bit of the guesswork out of fertilizer application because they do not depend upon fauna in the soil or temperature to work. However, testing the soil is always recommended when using organic or chemical fertilizers.

Home gardeners can feel confident when using these products because studies on their formulation and efficacy have been quite extensive. 

You can expect the advertised results to be reliably available when you follow packaging instructions.

Additionally, the instructions provided with these types of products are very detailed and precise, so you needn’t reinvent the wheel to use them.

Are There Any Down-Sides To Commercially Prepared Slow Release Fertilizer?

You must remember that these inorganic fertilizers are not natural and do not improve your soil. 

Sooner or later, your soil will be depleted no matter how many chemical amendments you use. You will need to add some truly natural organic material on a regular basis to help keep your soil healthy.

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Photo Credit: Instagram @leafessentials.cebu

What Is Coated Fertilizer?

Some products are termed “coated.” There are a number of different formulations of this type of product, but all of them provide the basic plant nutrition you would expect in a good fertilizer:

  • Ammonium Phosphate
  • Magnesium Phosphate
  • Calcium Phosphate
  • Ammonium Nitrate
  • Potassium Nitrate

..and more.

1. Nutricote fertilizer is granulated, and the granules are coated with a chemical release agent incorporated into a thermoplastic resin shell. Nutricote fertilizer (Amazon) is what many professional growers use because it REALLY WORKS.

The resulting pellets are typically tiny gray spheres. Depending on how the pellets were formulated and produced, they will release nutrients in a measured manner for as long as 12 months, given a soil temperature of 77 degrees Fahrenheit. Water also influences the rate of nutrient release. Look for the term “Nutricote” to identify this type of fertilizer.

2. Nutri-Pak style fertilizer was created by the University of Wisconsin. This type of product consists of a balanced nutrient solution contained in small, plastic packages that are intended to be dropped into the planting hole (perfect for root development) when new plants are introduced to the garden.

Packets are supposed to be active for as long as five years. While this certainly seems to offer some convenience, there are definite downsides to burying bits of plastic around your garden on a regular basis.

3. Osmocote is another form of granular slow-release fertilizer. It has been available to home gardeners in many different formulations for over three decades. Each specialized formulation is based in a balanced, complete fertilizer consisting of:

  • Ammonium phosphate
  • Calcium phosphate
  • Ammonium nitrate
  • Potassium sulfate

These slow release fertilizer granules are coated with alkyde resin (plastic) to create very small, yellow-brown spheres.

The coating of the granules can be varied to best suit the type of conditions where the product will be used. Also, results differ from one environment to another.

For example, the Osmocote 14-14-14 blend can last for 4-5 months at lower soil temperatures (60° degrees Fahrenheit). 

At higher temperatures, the nutrients are released faster, so you can expect the product to last for 3-4 months at temperatures of 70° degrees Fahrenheit and only 1-2 months at temperatures of 80° degrees Fahrenheit.

Osmocote is an excellent product for lower temperatures because this slow release fertilizer releases a greater amount of nutrients in cool soil than any other product.

4. Polyon is also available in several different formulations using standard fertilizer ingredients such as:

  • Ammoniated phosphates
  • Ammonium nitrate
  • Potassium nitrate
  • Potassium sulfate
  • Urea

Polyon pellets are typically green. Their polymer shell is very thin and very hard. In fact, it is almost impossible to break. 

As a result, release of nutrients is quite gradual. Temperature triggers nutrient release, and the product can be effective for as long as nine months at temperatures of 86° degrees Fahrenheit.

5. Sulfur-coated urea (SCU) is another form of slow-release fertilizer. It is available in two forms. The sulfur can either be sprayed onto granular urea in a molten form to create the fertilizer granules’ shell, or SCU can be provided on its own, encapsulated in polymer. Both of these products are very affordable and provide good nourishment for lawns, turfs, and gardens.

Costa  Comparison Among Fertilizers

When comparing the cost of a fertilizer product, you will get the most accurate results by calculating how much its nitrogen content costs per pound. 

To do this, you would multiply the total weight of the product by the percentage of nitrogen it contains. Divide the total cost of the product by the resulting number.

How Should You Use Slow Release & Controlled Release Fertilizers?

One of the main reasons many gardeners choose commercial slow release fertilizer products is that they are fast and easy to use yet provide long lasting results. 

Here is a brief guide to help you make the most of these handy products throughout your home, garden and yard:

1. Fertilizing Your Houseplants: You will need to keep a close eye on your plants to judge how quickly they are growing. You must also keep the season and the type of lighting you are using in mind.

Generally speaking, follow the instructions on product labels during the growing season (spring and summer) and dilute fertilizer to half during the dormant season (fall and winter).

If your plants are growing very rapidly and/or you have abundant sunlight or artificial light, you may want to increase the amount of fertilizer used during the growing season. This is especially true if you notice excessive yellowing of leaves.

2. Plant Food For Your Outdoor Container Plants: For outdoor plants, you will want to use a longer term, controlled, or slow release fertilizers. Begin fertilizing just before growth begins in the springtime. Choose according to whether or not your plants will remain in their pots throughout the growing season.

If you plan to transfer them, choose a shorter-term product (2-3 months effectiveness). If you plan to keep them in containers for the entire growing season, choose a product that will feed them for the entire season (3-4 months).

Learn More About Specialty Fertilizers Here

3. Lawn Fertilizer: The fertilizer for grass usually contains quite a bit of nitrogen (polymer coated or methylene urea or SCU) in a controlled-release form. This type of fertilizer is ideal for the very regimented lawn care required to keep grass looking good.

It’s smart to set up a regular schedule for lawn fertilizing using fertilizer like this best seller. Typically, it’s best to fertilize just before expected growth periods. This varies a bit from area to area. 

For example, in the northern US you would fertilize in the spring and fall to feed the cool season grasses that grow there.

In the southern US, you would feed your healthy lawn in the spring and summertime. This will help support southern grasses that thrive in warm weather.

In the north, a lawn needs around two or three pounds seasonally of actual nitrogen fertilizer per one-thousand square feet of surface area. Bermuda grass lawns in the southern states need double that amount.

Generally speaking, following package directions will yield good results. If in doubt, you can always consult with your coop extension agent to get specific instructions that are tailored to your situation.

4. Fertilizing Your Landscaping: It’s best to fertilize your landscape plants late in the winter or early in the spring in preparation for the growing season. 

With controlled or slow release fertilizers, this should be all you need for good foliage and healthy root systems in the spring and summer months. Another application during the fall will help keep your plants happy and comfortable during the winter.

If your plants are overcrowded, be sure to fertilize by scattering ten to fifteen pounds of controlled release fertilizer around them twice annually. If they are well spaced, and your soil is regularly amended, you can get away with feeding annually. If you decide to do this, be sure to feed generously.

5. Fertilizing Flowers: When fertilizing indoor flowers, use the same sort of schedule and methods you would use for houseplants. If your flowers are outdoor perennials or annuals, use the same strategies you would use for landscape plants.

Remember that it’s a good idea to provide nourishment when you plant. You can either scatter the fertilizer over the surface of the soil and water it in or work it into the first couple of inches of soil. Be careful not to let the undiluted product sit against the base of the plant, as it could cause damage.

6. Fertilizing Your Vegetable Garden: You may be surprised to know that some veggies do better with fast-release fertilizer. Examples include cold-weather vegetables like lettuce and radishes. The reason for this is that organic, slow release and controlled-release fertilizers all need warm soil to work well. Fast release fertilizer is perfect for cool soil.

For warm weather crops like corn and tomatoes, you should apply a 14-14-14 fertilizer with a 3-4 month controlled release when you plant. Work about ten pounds per 500 square feet into the soil.

Remember That All-Natural Organic Fertilizer Is Naturally Slow Releasing

When you use all organic compost and other completely natural soil amendments, you can build soil that is naturally rich and nourishing. 

However, this may take quite an extended period of time. If you are an aspiring organic gardener with poor soil, you may have to make some compromises to get started.

There are lots of organic materials that can both condition the soil and feed your plants in the long term. 

As you are getting started, you may want to enrich your soil with organic matter and carefully choose commercial slow-release and controlled-release fertilizing products to support successful gardening. You can gradually fade these from your practices as your soil quality improves.

Things To Consider When Choosing Commercial Fertilizers

When you are choosing chemical and/or commercial fertilizers to help supplement poor soil conditions while you build up your soil organically, it is important to understand the many ways in which chemical fertilizers can be detrimental.

We have discussed the fact that excessive use over time can actually deplete your soil and damage waterways, so when you are choosing supplements, you must look for those that are made with organic products as much as possible.

Additionally, it is wise to know the processes used in producing the products you buy. If the production of the product causes tremendous environmental damage, this negates any benefits to be had by using it.

Luckily, today greater environmental awareness has caused greater demand for more environmentally friendly commercial fertilizers made using naturally mined rock minerals and simple animal and plant matter.

Even though these products exist now, finding and identifying them can be challenging and complicated. The standards that are currently in place to differentiate chemical and organic fertilizers are complex.

You may see the word “organic” used on a number of products that are actually nothing but detrimental chemicals. To be sure of getting a higher quality and more natural product, look for these terms in the labeling:

  • Natural Organic
  • Slow Release
  • Low Analysis

Also, pay close attention to the ratio of organic NPK fertilizers. If a product is labeled as being organic, but the NPK ratio (nitrogen, phosphorus, potassium) total is higher than 15, it probably is not organic.

Remember that truly natural fertilizers have a lower NPK ratio because this ratio is based on nutrients that are immediately available. 

Natural fertilizers do not have a high percentage of immediately available nutrients. Instead, they release nutrients slowly over a long period. This is beneficial to all concerned!

Is It Hard To Use All-Natural Organic Fertilizers?

The convenience of chemical fertilizer is a big selling point, and many gardeners feel anxious about switching to natural fertilizing methods. Rest assured that using high-quality, natural organic fertilizer products is quite easy and very effective.

You can special blend your own mixtures if you want to and add a pinch of blood meal here and a touch of manure there if you like, but you don’t have to. 

These days there are a number of good all-purpose commercial natural organic fertilizers on the fertilizers market that you can use in every area of your yard and garden.

Modern Products Are Neat & Tidy

If you are worried that organic gardening will be messy, fear not! You will not need to shovel horse manure or scour the beaches for kelp. 

You can purchase both manure and kelp in dehydrated pellet form that is easy to toss about in the garden or even add to containers and house plants.

You can also find specialty organic fertilizers at high-quality garden centers and online. Some choices include organic mixes for:

As you learn more about organic fertilizers, you may wish to dabble in creating your own specialty mixes. Luckily, today you can buy all kinds of organic components, such as:

  • Chicken Feather Meal
  • Chicken Manure
  • Blood Meal
  • Green Sand
  • Bone Meal (Amazon) – details on Bone Meal uses
  • Fish Meal or Emulsion

…and more in tidy, easy-to-use packages.

Dry Organic Fertilizers Are Nicely Balanced & Naturally Slow Release

The advantage of using entirely natural dry fertilizer is that, unlike chemical fertilizers, it will not burn young plants.

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