Slow-Release vs. Quick-Release Fertilizer: What’s the Difference?
If you’re wondering why some fertilizers instantly boost plant growth while others last throughout the whole season, this article explains the differences between slow-release and quick-release fertilizers and how to choose the best products for specific plants.
![quick vs slow release fertilizer. Close-up shot of two hands pouring organic granular fertilizer onto a young sprout in the soil, in a sunny garden, against a blurred green background. This sprout has a thin vertical stem and a couple of cotyledons, which are oval, smooth, and green. Granular fertilizers are round in shape and come in different colors: white, blue, pink and black.](https://www.epicgardening.com/wp-content/uploads/2024/03/quick-vs-slow-release-fertilizer.jpeg)
Contents
With all the letters, dosages, deficiencies, and chemistry jargon, the world of fertilizers can be quite confusing. Thankfully, you can simplify how you feed your garden by applying basic concepts of plant nutrition and natural soil processes. There are thousands of fertilizer products on the market today, but every single one fits into one of these categories: slow-release or quick-release.
The category of fertilizer you choose from ultimately determines how fast your plant can uptake the nutrients and how often you have to reapply. It can also have major impacts on your local ecosystem and the health of your soil.
Let’s dig into the key differences between slow-release and quick-release fertilizers.
The Short Answer
![Close-up of a gardener's hand adding dry horse dung fertilizer to the base of a cucumber plant. The cucumber plant is a fast-growing annual vine with sprawling stems and large, lobed leaves. These leaves are dark green, with finely serrated edges.](https://www.epicgardening.com/wp-content/uploads/2024/03/farmer-giving-dry-horse-dung-fertilizer-.jpeg)
Slow-release fertilizers are organic, while quick-release fertilizers are synthetic. Imagine slow-release fertilizers as a gradual trickle of nutrients over a longer time period, while quick-release fertilizers give one megadose that lasts for a short time.
The majority of slow-release fertilizers are organic, which means they contain carbon and require microorganisms to break them down into plant-available nutrients. Slow-release fertilizers include compost, bone meal, fish emulsion, blood meal, alfalfa meal, and manure.
On the other hand, most quick-release fertilizers are synthetic, which means they are manmade and do not contain carbon. They bypass microbial breakdown, so they are instantly available to plants but dissipate quickly, requiring more frequent applications. Quick-release fertilizers include urea, ammonium nitrate, and superphosphate.
Organic slow-release fertilizers feed the soil, and synthetic quick-release fertilizers directly feed the plant. Your gut reaction may be to choose the latter, but once you understand the importance of a thriving soil microbiome in your garden, you may find yourself reaching for organic options because they contribute to lasting sustainability.
Comparison Chart: Slow-Release vs. Quick-Release Fertilizer
Slow-Release | Quick-Release |
Typically organic | Typically synthetic or manmade |
Longer-term plant nutrition | Short-term nutrients |
Require microbial breakdown | Instantly plant-available |
Feed the soil | Feed the plant |
Less frequent applications | More frequent applications |
Less likely to leach into groundwater | Higher risk for nutrient leaching |
Less risk of overfertilizing | Higher risk for “fertilizer burn” |
Typically come from natural resources | Mostly sourced from petroleum byproducts |
The Long Answer
The fundamental difference between these fertilizers is the rate of nutrient delivery to the plant. Slow-release fertilizers gradually make minerals and nutrients available to the plant over time, creating a more balanced soil ecosystem. Rapid-release fertilizers are highly water-soluble and provide an instant dose of nutrients.
Both types of products come with pros and cons, but the eco-minded organic gardener most often chooses slow-release fertilizers because they pose less environmental harm and require less frequent applications.
Here we’ll dig deeper into the pros and cons of each type, including plenty of examples and scientific data.
Slow-Release Fertilizer
![Close-up of a farmer giving organic fertilizer to young plant. These organic fertilizers consist of dry, crushed leaves. The young plant has pale green lobed leaves.](https://www.epicgardening.com/wp-content/uploads/2024/03/Farmer-giving-organic-fertilizer-to-young-plant-.jpeg)
The primary benefit of slow-release fertilizer is that it provides a steady amount of nutrients over time. You don’t need to apply it very often, and you don’t typically need to worry about fertilizer burn. While there are a few synthetic slow-release fertilizers (such as urea-formaldehyde), most truly slow-release fertilizers are organic.
The organic options are more natural and don’t require complex chemistry to understand. Mother Nature has been decomposing leaves, manure, and other dead plant or animal residues for billions of years before humans invented fertilizer. Plants have evolved age-old collaborations with soil microorganisms to decompose and consume these nutrients.
Soil is Like an External Digestive System
![Close-up of Earthworms in soil with compost. The compost is moist, lumpy, earthy, dark brown in color with kitchen scraps and long red-purple worms.](https://www.epicgardening.com/wp-content/uploads/2024/03/nutrient-rich-compost.jpeg)
Imagine organic plant nutrients (for example, the nitrogen and phosphorus in manure) as little bundles of food with a special lock on the outside. Plants cannot immediately “unlock” the food capsules and “eat” them because soil microbes have the key. Soil microbial communities like beneficial bacteria and fungi are necessary to break down the nutrients into plant-available forms.
In other words, the soil microbiome is sort of like an external digestive system for plants. Much like the microbiome of the human gut, beneficial soil microbes act like intermediaries to help plants digest their food. This is why slow-release fertilizers are gradually accessible over a longer period of time. It takes time for microbes to decompose the materials.
If your soil is lacking in microorganisms (or you are growing in a container), it may take even longer for plants to access the nutrients because there aren’t many organisms working in the soil. This can be remedied by using compost, worm castings, soil inoculants, and compost teas. Overall, soils with more microbial activity are better at processing slow-release fertilizer nutrients.
If you want to mimic nature and garden organically, slow-release fertilizers are the best products for you. Still, they can come with a few drawbacks to consider.
Examples of Slow-Release Fertilizer
![Close-up of a small garden trowel with a wooden handle scooping up manure on a blurred green background. Manure fertilizer is a natural soil amendment derived from animal waste. It has a crumbly texture and a light brown tint.](https://www.epicgardening.com/wp-content/uploads/2024/03/Manure.jpeg)
These fertilizers gradually release plant nutrients to maintain balanced plant nutrition over the entire lifecycle of a crop. They can also improve soil health over time.
Examples include:
- Compost
- Manure
- Organic all-purpose fertilizer
- Fish meal and fish emulsion
- Seaweed
- Kelp meal
- Bone meal
- Blood meal
- Bat guano
- Alfalfa meal
- Cottonseed meal
- Worm castings (vermicast)
- Some synthetic fertilizers, such as urea-formaldehyde or methylene urea
Pros
The science-backed benefits of slow-release organic fertilizers have prompted sustainable gardeners and farmers to switch to organic fertilizers for healthier soil and stronger crops. The pros of these products include:
Prolonged Nutrient Supply (Less Frequent Applications)
![Hands of a young girl with fresh soil in the garden on a blurred background. The girl pours fresh soil from one hand to the other. The soil is loose and black.](https://www.epicgardening.com/wp-content/uploads/2024/03/farmer-hand-holding-soil.jpeg)
Organic fertilizers create long-lasting soil fertility, so you don’t have to apply them as often. If you’re a lazy gardener, you’ll be glad to know sometimes you only need to apply them once or twice per year. They provide sufficient nutrition for your plant over a longer time period, which means you don’t need to repeatedly fertilize.
Anyone who has tended a high-maintenance lawn knows how annoying constant fertilizer application can be. Slow-release all-purpose products allow you to feed your plant and forget about it for a while.
More Balanced Nutrient Ratios
![Close-up of a woman's hand in a blue glove sprinkles ash on radish sprouts. Radish sprouts have rosettes of bright green, lobed leaves. Ash fertilizer is a natural soil amendment produced by burning organic materials such as wood, leaves, or crop residues.](https://www.epicgardening.com/wp-content/uploads/2024/03/a-womans-hand-sprinkles-ash-on-a-radish-sprout.jpeg)
Organic fertilizers tend to be more balanced in their nutrients, while synthetic fertilizers may pose issues with nutrient deficiencies or overdoses. For example, an all-purpose organic blend like Espoma Garden-Tone Organic Plant Food is derived from feather meal, poultry manure, bone meal, greensand, and potash (wood ashes). The blend of these materials creates a balanced NPK analysis of 3-4-4. When the ratios of nitrogen, phosphorus, and potassium are close together, this means the fertilizer provides balanced nutrition.
For comparison, quick-release nitrogen, like synthetic urea, has an NPK ratio of 46-0-0. You can see how this could quickly create a huge imbalance in the soil!
Balanced plant nutrition is important because excess amounts of certain nutrients can actually make other nutrients unavailable to plants. For example, soils with too much potassium can “tie up” micronutrients like boron and manganese. If you apply a quick-release synthetic potassium fertilizer like potassium chloride (0-0-60), it could lead to a deficiency in boron or manganese.
These complex interactions have to do with the mobility or immobility of certain minerals in the soil. Without digging too deeply into soil chemistry, suffice it to say that nature does the hard work for you. Most slow-release fertilizers deliver even ratios of nutrients rather than a spike in a single nutrient.
Support Healthy Soil Organisms
![Close-up of a man's hands adding compost to a young tomato seedling in the garden. This young seedling consists of compound leaves composed of multiple leaflets. The individual leaflets are generally lance-shaped and arranged alternately along the stem, with serrated margins.](https://www.epicgardening.com/wp-content/uploads/2024/03/Human-hands-and-tomato-seedling.jpeg)
Organic fertilizers don’t just feed your plants; they feed the soil organisms. Remember the external digestion analogy from above? While microorganisms work to digest nutrients for plant roots to uptake, they are simultaneously building soil structure and long-term fertility. The minerals from slow-release fertilizers enhance microbial populations to create a healthy, self-sustaining ecosystem belowground.
A diverse, abundant soil microbiome is directly linked to greater soil resilience and higher plant yields. Tiny soil organisms like bacteria, fungi, protozoa, beneficial nematodes, spiders, worms, and beetles are all vital members of your garden ecology. In addition to fueling plant growth, they help your plants withstand periods of drought, extreme weather, and pest or disease pressure.
Less Risk of Overfertilizing
![Close-up of a gardener's hand in a white glove full of granular fertilizer over a bed of young beet plants. These granular fertilizers are round in shape and grayish in color.](https://www.epicgardening.com/wp-content/uploads/2024/03/Young-adult-woman-palm-holding-complex-fertiliser-granules-for-beets.jpeg)
Overfertilizing can be detrimental to houseplants, vegetables, flowers, and trees. In mild cases, it can reduce flower production or reduce the aromatic fragrance of an herb. In extreme cases, overfertilizing can cause a plant to turn brown and yellow or completely die.
Gradual-release fertilizers are far less likely to “burn” your plants. These balanced, organic products provide a slow trickle of nutrients over time, so your plants aren’t blasted with massive amounts of nitrogen or potassium at one time.
Keep in mind that you still need to follow package directions. Never dump large amounts of fertilizer on any plant. Slow-release fertilizers can still cause overfertilization symptoms, but it is less likely.
Natural and Organic
![Close-up of a gardener's hands holding soil mixed with compost next to a compost pile. The compost pile consists of kitchen scraps.](https://www.epicgardening.com/wp-content/uploads/2024/03/Compost-in-hands.jpeg)
If you love nature, this benefit is very straightforward: slow-release organic fertilizers come from the Earth, while quick-release synthetic fertilizers are manmade and typically come from a chemistry lab at a fertilizer factory.
Minimal Nutrient Leaching (Better for the Environment)
![Close-up of a cow manure on green grass in a sunny garden. Natural compost material in a meadow. Cow manure is a natural fertilizer and soil amendment composed of decomposed organic matter from cattle waste. It appears as dark brown, crumbly material.](https://www.epicgardening.com/wp-content/uploads/2024/03/cow-manure-in-a-field-.jpeg)
Leaching is one of the biggest issues in the world of modern fertilizers. Rapid-release synthetic fertilizers are highly water-soluble, which means they are easily “flushed” out of the soil with rainfall or irrigation. These quick-release fertilizers (particularly nitrates) flow into groundwater, rivers, and ultimately the oceans, causing widespread devastation for fish and aquatic life. They are the primary reason for massive aquatic destruction, such as the Dead Zone in the Gulf of Mexico.
In contrast, gradual-release organic products are less likely to contaminate the groundwater because they are water-insoluble. They don’t dissolve readily in water. They naturally bind to soil particles and remain more stationary in the garden. Because slow-release materials require microbial breakdown, they are less likely to megadose a waterway with excessive nutrients that can imbalance the aquatic ecosystem. Organic fertilizers cause less pollution than synthetic ones.
Research shows that organic inputs reduce nutrient leaching and runoff by up to 30%. Other studies have confirmed that nitrate leaching is up to five times higher in conventional synthetic-fertilized plots versus organic ones. In other words, organic slow-release fertilizer is 5 times less likely to leach into the groundwater. This means far less pollution risk for the surrounding ecosystem!
However, beware that high amounts of improperly managed manure can also cause nutrient-leaching issues. It’s best to compost or age manure before using it in your garden and protect your piles from excessive rainfall. This is especially important if you live near a water source such as a pond or river.
Cons
The main drawbacks to gradual-release fertilizers are their timing, solubility, and a few ingredients with controversial sourcing.
Insoluble in Water
![Close-up of a gardener's hands adding organic granular fertilizer to a young plant in the garden. This plant has a thin stem with compound leaves, which consist of oval, jagged leaflets of green color. Granular fertilizers are round and yellow in color.](https://www.epicgardening.com/wp-content/uploads/2024/03/young-plant-in-soil-with-fertilizer.jpeg)
Slow-release organic fertilizers are mostly insoluble, which means they don’t readily dissolve in water. While there are some great liquid products (like liquid fish emulsion), most slow-release fertilizers are granular, pelleted, or ground up like compost.
The insolubility is why these products are less likely to leach into waterways (which is a good thing!) But it can also be problematic for some gardeners, specifically container gardeners, houseplant growers, and people using fertigation (liquid fertilization through drip lines).
Soil microbes are required to convert organic fertilizers into water-soluble forms. If your soil is lacking in soil microbes, slow-release fertilizers may have a difficult time breaking down. Plants could display signs of deficiencies because they are unable to uptake the fertilizer. This is yet another reason to prioritize amending with organic materials like compost and cover crops!
If you are growing indoors in containers without much microbial activity, consider using a more readily available organic fertilizer like Espoma Organic Indoor Plant Food.
Slower-Acting
![Close-up of a gardener pouring liquid fertilizer from a jar onto young cucumber plants in the garden. This liquid fertilizer is brown in color. Young cucumber plants have heart-shaped green leaves with finely jagged edges.](https://www.epicgardening.com/wp-content/uploads/2024/03/Woman-pours-liquid-mineral-fertilizer.jpeg)
The biggest drawback to organic fertilizers is that they require more patience. If your plant is yellowing due to a lack of nitrogen, a slow-release fertilizer won’t perk it back up in a day. It may take two to four weeks, depending on conditions.
Take note that some organic fertilizers like seaweed and fish emulsions release nutrients more rapidly than something like compost. This is because they are in liquid form and readily soluble. If you need a fast-acting fertilizer but still want to use organic products, choose a marine-based fertilizer like liquid fish or kelp. These options are great for helping a houseplant recover or supplying nutrients to a dying tomato plant.
However, just because they are organic doesn’t mean they can’t burn the plant. Never add large amounts of these fertilizers to your plants. Follow package instructions and avoid over-fertilizing, as this can still “burn” the crop.
Some Unsustainable Resources
![Close-up of Worm castings organic fertilizer with a small garden trowel. Worm castings organic fertilizer, also known as vermicompost, is a nutrient-rich soil amendment produced by earthworms. It appears as dark, crumbly material with a fine, granular texture resembling coffee grounds.](https://www.epicgardening.com/wp-content/uploads/2024/03/Worm-castings-organic-fertilizer.jpeg)
Some organic fertilizers, like bat guano or greensand, have sustainability and sourcing issues. Bat guano is controversial because of the bat diseases spread by guano collectors in bat caves. In conjunction with habitat damage and urbanization, these diseases are contributing to global declines in bat populations.
As an alternative, we recommend using worm castings because they are cheap, readily available, and easy to collect from a DIY home worm bin. You can also install bat boxes in the trees surrounding your garden.
Greensand is another organic fertilizer with potential environmental concerns. It is a completely natural slow-release potassium fertilizer that contains a wealth of trace minerals. However, it is mined from 80 million-year-old marine deposits that are nonrenewable. Once all the greensand is mined, there won’t be any left because it takes so long to mineralize belowground. Kelp meal is a great renewable alternative.
Quick-Release Fertilizer
![Close-up of chemical fertilizers in a black metal scoop with blue granular fertilizers near growing watermelon plants. The watermelon plant is a sprawling, vine-like annual with large, lobed leaves that grow in a trailing manner along the ground.](https://www.epicgardening.com/wp-content/uploads/2024/03/Chemical-fertilizer-placed-on-the-ground-with-watermelon-plants.jpeg)
The biggest problem with quick-release fertilizer is the potential for environmental pollution. It can also cause issues with nutrient “burn” from overfertilizing your plants. However, some landscapers and container gardeners still prefer these products because they rapidly release nutrients into the root zone, effectively bypassing the need for microbial decomposition.
Here are the main pros and cons of synthetic plant nutrients, with examples and scientific research.
Examples
![Close-up of a gardener's hand in a blue glove pouring white granular fertilizer into the soil in the garden. These fertilizers consist of a bunch of tiny round balls.](https://www.epicgardening.com/wp-content/uploads/2024/03/Pouring-granulated-fertilizer-under-bushes-in-garden.jpeg)
Quick-release synthetic fertilizers are inorganic compounds. In chemistry, inorganic means a compound does not contain carbon. Coincidentally, these products are also not suitable for organic farming because they contain manmade synthetic chemicals.
Most of these fertilizers are made of byproducts from the petroleum industry. This may not be readily advertised on the package, but you should be able to look at the ingredients of a product blend to find the scientific names of the ingredients.
Quick-release fertilizer ingredients include:
- Urea
- Ammonium nitrate
- Ammonium phosphate
- Diammonium phosphate
- Potassium chloride
- Potassium sulfate
- Superphosphate
Pros
The key benefits of rapid-release fertilizers are quick absorption and advantages for potted plants.
Quick Absorption
![Close-up of a gardener's hand in a blue glove full of chemical fertilizers over a young seedling in a sunny garden. Chemical fertilizers have a fine structure that resembles wet salt. The young seedling has round green leaves with jagged edges.](https://www.epicgardening.com/wp-content/uploads/2024/03/gardening-hand-holding-fertilizer-close-to-soil-.jpeg)
The name of these fertilizers is a major giveaway: they quickly release nutrients into the plant root zone, which means the plants can rapidly absorb the “food.” There is no need for synthetic fertilizers to go through the “soil digestive system” to get to the plants. These chemical compounds are already “available” for plants to uptake right away.
If your plant is yellowing, necrotic, or lacking in flowers, a quick flush of fast-release fertilizer could provide very quick recovery, sometimes as fast as a few days to one week. Conventional farmers regularly use quick-release fertilizer because it boosts their crops instantly. However, organic farmers are not allowed to use synthetic products in their fields, so they must plan more to ensure that soil fertility is sufficient before planting.
If your soil is extremely poor, a quick-release fertilizer provides quick relief for nutrient-deficient plants. But you must beware that it won’t create lasting fertility the way that organic fertilizers do. In fact, the “quick fix” could actually cause your garden to have more problems over time.
Solubility in Water
![Close-up of a woman in yellow gloves pouring liquid chemical fertilizer into a large blue watering can in a sunny garden. A gardener pours fertilizer from a yellow bottle.](https://www.epicgardening.com/wp-content/uploads/2024/03/Woman-pours-liquid-mineral-fertilizer-into-watering-can.jpeg)
The solubility of quick-release fertilizers is a benefit for growers who need to instantly boost a plant or brighten a dying lawn. These products readily dissolve in water or come in a liquid form. They are easy to mix in a watering can or flow through a fertigation system.
More Precise Nutrient Ratios
![Close-up of a gardener's hand in a white glove pouring granular fertilizer from a wooden shovel into the soil in the garden. Granular fertilizers are small white-gray balls.](https://www.epicgardening.com/wp-content/uploads/2024/03/Granulated-mineral-fertilizer-.jpeg)
Advanced plant chemistry has made modern fertilizers extremely precise about their nutrient ratios. While the mineral nutrients of compost can vary widely based on the ingredients, the nutrients inside a synthetic fertilizer are very pinpointed.
Good for Houseplants
![Close-up of applying granular fertilizer to a potted plant indoors. There is a handful of brown granular fertilizer on the small iron spatula. The plant grows in a large clay pot.](https://www.epicgardening.com/wp-content/uploads/2024/03/Applying-a-fertilizer-on-the-potted-plant-at-home.jpeg)
Many houseplants and orchid growers prefer synthetic fertilizers because they are the industry standard for nurseries. The rapid release of nutrients is easy for promoting big blooms or helping a plant recover. However, as you’ll see below, this can also come with some major risks, like fertilizer burn or constant reapplications.
Cons
Quick-release fertilizers pose major issues for environmental sustainability, leaching, salt buildup, and the potential to burn your plants.
In my opinion, the risks of rapid-release fertilizer are not worth it. Organic gardeners should avoid these products. Nature already gave us all the fertility we need in the form of healthy soil amended with plant and animal byproducts!
Leaching Environmental Pollution
![Close-up of a green garden trowel with granular mineral fertilizers on the soil. Granular mineral fertilizer is a solid, dry substance typically made up of small, uniform pellets or granules with varying colors depending on the specific nutrients they contain: blue and yellow. These pellets are spherical.](https://www.epicgardening.com/wp-content/uploads/2024/03/mineral-fertilizer-.jpeg)
The high solubility of quick-release fertilizers means they are highly prone to leaching. When rain or irrigation water hits your front lawn or garden soil, synthetic fertilizers can easily runoff or leach out. Where do they go? Into the groundwater, where they can cause major environmental pollution that harms wildlife and contaminates drinking water supplies.
The Dead Zone in the Gulf of Mexico is a prime example of the ecological disasters caused by modern synthetic fertilizers. When excessive amounts of nitrates are applied to farm fields in the Midwest and Mississippi River basin, the rain washes excess fertilizer into the groundwater and streams. This water, full of fertilizer runoff, ends up in the Mississippi River, which flows to the Gulf of Mexico.
When the nutrient-heavy water reaches the gulf, it causes a problem called eutrophication. The excessive amounts of synthetic quick-release fertilizer fuel a sudden bloom in algal growth. This algae covers the ocean surface, effectively killing everything beneath it. The hypoxic (oxygen-devoid) zone below kills off all the fish and other aquatic life. As of 2023, the Dead Zone is over 4,000 square miles in size. In past years, it expanded to over 8,000 square miles.
If you care about oceans and clean, safe drinking water, consider avoiding synthetic quick-release fertilizers!
Frequent Applications Required
![Close-up of a man's hand applying fertilizer to a tomato seedling in the garden. Fertilizers are granulated, they are in the form of rounded gray pallets. The tomato plant consists of green compound leaves that are composed of oval leaflets with jagged edges.](https://www.epicgardening.com/wp-content/uploads/2024/03/Small-gardens-with-beautiful-different-green-flower.jpg)
The most annoying thing about quick-release fertilizers is their neediness: they must constantly be reapplied! The rapid release also means rapid decomposition. As plants use up the nutrients, they quickly become hungry for more.
While slow-release organic fertilizers build up soil fertility over time, synthetic products create a constant need for reapplication. Once you become accustomed to feeding plants with synthetic nutrients, you are stuck on a sort of “fertilizer treadmill”: you have to keep buying more fertilizer and apply it many times throughout the season. This isn’t only higher maintenance; it results in a higher risk for issues like overfertilization or leaching.
Salts
![Close-up of woman's hands holding fresh soil in the garden. The gardener is wearing a beige sweater. The soil is loose and black.](https://www.epicgardening.com/wp-content/uploads/2024/03/Hands-of-farmer-showing-black-soil-.jpeg)
The residual salts from excessive synthetic fertilizer use can harm soil health. In other words, synthetic fertilizers contain salts that hurt soil microbes and reduce soil fertility over time. This is why modern industrial agriculture faces such tremendous challenges with soil health and sustainability. After decades of synthetic fertilizer application, the soil of some crop fields becomes completely degraded and no longer farmable.
Risk of Nutrient Burn
![Close-up of green grass and chemically burnt grass in the garden. Grass appears as a lush, dense carpet of thin, blade-like leaves that emerge from the soil in tufts. Chemically burned grass appears brown and has a wilted and scorched appearance.](https://www.epicgardening.com/wp-content/uploads/2024/03/chemical-burned-grass.jpeg)
Over-fertilizing is a major risk with quick-release fertilizers because these products tend to be highly concentrated. The result is nitrogen “burn” or fertilizer “burn” because the plant receives an overdose of nutrients that it cannot process. Imagine it as similar to taking an outrageous amount of vitamins at one time (bad idea!)
When a plant is doused in a concentrated synthetic fertilizer, it can cause rapid wilting, yellowing, browning, leaf drop, or plant death. While you can over-fertilize with any product, it’s particularly risky with rapid-release nutrients because they megadose the plant all at once.
Synthetic With Petroleum Byproducts
![Close-up of a gardener's hands in blue gloves holding a handful of granular fertilizer over a large bag of fertilizer. These fertilizers are granular, round in shape, and come in different colors: white, grey, red and beige.](https://www.epicgardening.com/wp-content/uploads/2024/03/Farmer-holding-granulated-fertilizer.jpeg)
The majority of synthetic fertilizers are man-made from petroleum byproducts. Synthetic nitrates are even manufactured using a similar process to the nitrogen bomb! After World War I, the government had a lot of leftover ammonium nitrate that was originally used for explosives in the war. They realized that it could be used as a nitrogen fertilizer and began selling it to farmers.
Most modern-day quick-release fertilizers are still made with the same Haber-Bosch process used in WWI. This method for producing synthetic nitrates uses high pressures and high temperatures to synthesize ammonium nitrate. This process alone is estimated to contribute to nearly 2% of global carbon dioxide emissions every year.
So, if you’ve ever heard of fertilizer plants exploding or barns catching on fire, now you know why! Quick-release nitrogen (specifically ammonium nitrate) is highly flammable and explosive because it was originally developed for wartime use.
If you want to keep petroleum and explosive ingredients out of your garden, choose slow-release fertilizers instead.
Final Thoughts
Ultimately, the differences between these two types of plant nutrients are fairly clear in their names. Slow-release provides a gradual trickle of nutrients, while fast-release is an instant dose.
However, it’s more important to understand that slow-release fertilizers are typically organic and more sustainable for use in a home garden. They require fewer applications and naturally improve soil health over time.
Rapid-release fertilizers tend to be synthetic and pose risks for environmental pollution, over-fertilizing, and reduced soil health. But some container gardeners and landscapers still prefer the latter because it is fast-acting.