When it comes to deciding on the right fertilizer for your plants, choosing between organic vs inorganic fertilizer is an open debate. Each has strengths and weaknesses – but you don’t have to use only one type. In this article, we’ll explain the facts and help you make an informed decision.
Inorganic fertilizers are manufactured, concentrated, and inexpensive, but often lack trace elements. Organic fertilizers are made from natural products such as worm castings, seaweed, or compost. They cost more but are safer to apply and offer a wider range of nutrients.
Overview Of Organic Vs Inorganic Fertilizer
Plants get most of their nutrition from photosynthesis, but they do require certain physical chemicals to aid the process. Most plants acquire these elements from the soil through their roots; many absorb nutrients through their leaves, too.
We can optimize plant growth by supplying necessary nutrients with regular fertilization. Some plants consume more than others: each species needs a specific feeding regimen.
There are two categories of fertilizer:
Organic fertilizers are made from a variety of natural products, from wood ash to worm castings to kelp. Organics are the oldest form of fertilizers and have the advantage of delivering a broad array of nutrients in a form friendly to plants.
Inorganic fertilizers are synthetic products. They are manufactured to contain a specific subset of plant nutrients. These fertilizers are quantifiable and relatively inexpensive.
There isn’t necessarily a right or wrong choice: both types of fertilizer have benefits and limitations!
Organic Vs Inorganic Fertilizer Summary
| Property | Organic Fertilizer | Inorganic Fertilizer |
| Ease Of Use | Often more messy to use and may have an offensive odor | Easy to apply, but highly concentrated, so care needed to avoid over-application. Come in a wide variety of forms. |
| Storage | Can be bulkier to store and may spoil | Easy to store and usually have a long shelf-life. |
| Nutrient Content | The nutrient content is less precise, but often contains a wider range of micronutrients. | Concentrated and precise concentrations. Wide variety of options. |
| Rate Of Nutrient Release | Broken down slowly in the soil to release their nutrients. More difficult to predict the rate of nutrient release. | Most provide immediate nutrient availability, although slow-release options are available. |
| Impact On Soil | Can improve the soil quality, structure, and enhance the microbiome. | No significant benefit to the soil, and can negatively impact the soil microbiome. |
| Price | Usually more expensive and less concentrated. | Usually much more affordable. |
| Safety | Generally safe for plants, people, and pets. | Easy to harm plants by overapplication. Essential to store safely away from children and pets. |
Fertilization Basics
There are 17 essential nutrients for plant growth – but these aren’t consumed in equal amounts. The three elements most heavily used by the plant are called macronutrients; they perform many vital biochemical functions within the plant and tend to be depleted first.
Macronutrients
Nitrogen (N) – A major component of chlorophyll, nitrogen is the element the plant needs in the largest amounts. It assists in photosynthesis, building proteins, energizing the plant’s system, and the production of leafy growth. A lack of nitrogen is the most common nutritional deficiency; its lack causes yellowing and stunting of foliage.
Phosphorus (P) – This element plays a part in photosynthesis and aids energy transfer within the plant’s system. Every plant cell contains this vital chemical, and a deficiency causes poor growth and stunted fruit and seeds.
Potassium (K) – Photosynthesis and cell production also depend upon adequate quantities of potassium. The element has a crucial role in the transport of energy and material within the plant, and it controls the opening and closing of stomata. Insufficient potassium causes poorly developed stems and roots, yellowing of the foliage, and leaf loss.
Micronutrients
Plants also need lesser amounts of important micronutrients like sulfur, magnesium, and calcium. Besides the micronutrients included in the 17 elements essential to plants, there are a host of ostensibly optional – but possibly useful – chemicals used in tiny amounts.
There isn’t a standard labeling format for micronutrients, and they are often missing from inorganic fertilizer packaging. In fact, the presence of a variety of micronutrients and trace elements is one of the main differences between inorganic and organic fertilizers.
Synthesized formulas sometimes contain only the big three macronutrients, although some contain additional micronutrients, whereas natural blends contain a diversity of nutrition.
A lack of micronutrient supplements isn’t necessarily a big deal: lesser-used elements are needed in such small quantities that sufficient amounts may already exist in the soil.
NPK Ratio
The three macronutrients are so important that retail fertilizers use a standardized format to list them on their labels. This convention, three numbers separated by dashes, is called the NPK ratio after the macronutrients’ chemical abbreviations.
The NPK numbers represent the proportion of each macronutrient in the fertilizer. A balanced set of numbers, such as 2-2-2 or 10-10-10, indicates an equal proportion of each element.
The absolute size of the numbers represents the amount of that chemical in relation to the whole quantity. Organic sources typically have lower NPK numbers than inorganic fertilizers.
Other Fertilization Factors
Successful fertilization involves more than the application of nutrients:
Bio-Availability
It doesn’t matter if a nutrient is abundant if the plant can’t use it. Like a thirsty sailor in an ocean of seawater knows, an element is only truly present if it’s in an accessible form.
There are two main ways a nutrient can be impossible for a plant to use:
- An element can be chemically structured in a form that roots can’t readily assimilate and put to work in the plant. Inorganic fertilizers can list ingredients that are technically present but impossible for the plant to use.
- The Bio-availability of nutrients can be affected by the soil’s pH, which is why you see specific pH ranges listed for different plants. Iron, for example, is easily assimilated in acidic conditions and becomes increasingly difficult for a plant to process as soil alkalinity increases. The pH can be tested and adjusted to the plant’s preferred range.
Safety
Nutrients can be supplied in such overabundance that they actually toxify the soil and prevent absorption or damage the roots.
This can happen even if you haven’t recently fertilized. An adjustment of pH can suddenly make elements available in quantities that overload the plant’s system. Slow-release formulas in the soil can be difficult to time, especially if the plant is new, and may lead to unsuspected overfertilization.
The danger of root burn can be lessened by buffering chemicals present in organic sources. Be sure to dilute synthetic fertilizers before application, and flush the soil routinely to remove unused product.
Nutrient Diversity
Natural soil contains a much larger range of elements than the ones a plant requires. Nutrient diversity is healthy: fertilizers with a wide variety of ingredients contribute to a more robust plant.
Some manufactured fertilizers contain just the three macronutrients with perhaps a few micronutrients thrown in. Even if the formula contained all 17 essential nutrients, they still wouldn’t provide the many beneficial trace elements a plant will use but can survive without.
The Microbial Ecosystem
Microbes inhabit the soil and play an important role in maintaining its health and fertility. Research is continually uncovering more information about how a vibrant microbial community benefits plants.
This invisible ecosystem is naturally present in soil and can be nourished through fertilization. Organic materials do better than inorganic formulas at providing varied nutrition to help the microbial population flourish.
If you’d like to learn more, I’ve written another article covering how fertilizer works in more detail.
Inorganic Fertilizers
One of the most important modern innovations for agriculture and gardening has been the development of synthetic fertilizers. Made of inorganic material, these manufactured compounds provide a concentrated, exact formulation of the most commonly needed nutrients.
Inorganic fertilizers are typically water-soluble and easily absorbed by the plant. They are generally fast-acting, though there are slow-release formulas, too.
Countless brands of synthetic fertilizer on the market can produce great results – with a few caveats.
Inorganic Fertilizer Advantages
Inorganic Fertilizers Are Easy to Use
There is little guesswork involved with manufactured fertilizers. They are made in a laboratory and the labeling is accurate.
If your plant requires more nitrogen, a synthetic formula can provide it quickly and precisely. Inorganic fertilizer is simple to measure and typically easy to dilute in water.
Uncomplicated Storage
Because inorganic fertilizer is so concentrated, it takes up less space. Manufactured formulas come in convenient sizes. Also, they aren’t subject to rapid deterioration.
Finally, the concentrated nature of synthetic fertilizers makes them unattractive to pests and animals, so they don’t need to stay securely locked up.
Inorganic Ferilizers Are Inexpensive
Manufactured fertilizers are cost-effective in comparison with organic products. They are produced by large-scale manufacturing that takes advantage of economies of scale.
Because they are concentrated, inorganic fertilizers also go farther per pound then organic products.
Precise Ingredient Listing
Inorganic fertilizer can boost a fast-growing plant with what it needs most: macronutrients. Because synthetic fertilizer is created through a controlled chemical process, it produces an exact end product.
Using inorganic fertilizer, you can dose your plants with great precision. This exactness is helpful when trying to correct soil for macronutrient deficiencies.
Disadvantages of Inorganic Fertilizers
Incomplete Range of Nutrients
The downside of synthetic manufacturing is that it limits the fertilizer to a few specific ingredients, typically the macronutrients. Some manufacturers include a selection of micronutrients, but it doesn’t erase the essential sterility of inorganic products.
The assumption is that the soil will already contain sufficient micronutrients for plant health: industry is giving a nod to the importance of organic matter to plants.
Bioavailability Issues
Many elements can exist in a chemical structure that plants cannot interact with. What’s more, an inorganic fertilizer can list an ingredient even if it’s not in a form the plant can use.
Reputable fertilizers are unlikely to have this problem; but, without doing research, it is difficult for gardeners to know if they are buying effective fertilizer or a powder made of fillers.
Inorganic Fertilizers Are Easy To Overuse
The concentrated nature of synthetic fertilizers makes it easy to overfeed a plant. Overfertilization can toxify the soil and harm roots, causing stunting and brown leaves.
To apply inorganic fertilizers safely, apply sparingly using only half or a quarter of the label’s recommendation.
Pro Tip: Water the plant a day before fertilizing so that the soil is moistened and the roots are well-hydrated.
Lack of Microbial Nutrition
Since synthetic fertilizers are concentrated formulas with an incomplete range of nutrients, they can leave the soil’s microbial population undernourished and foster an imbalance of organisms. A poor microbial community can result in less healthy soil.
Organic Fertilizers
Organic fertilizers are made from plant or animal products. This is the oldest category of fertilizers: organic fertilizers have been used for thousands of years. Because of this, organic fertilizers have a great deal of lore attached to them … some of this is still valuable.
Plants evolved using organic sources, so this kind of fertilizer is especially plant-friendly. Organic matter also tends to improve the soil’s structure and water transmission. It won’t cake on top of the soil, either.
Many organic fertilizers aren’t as consumer-friendly as synthetic retail products and may seem old-fashioned, but they will never be outdated … because plants love them. You can read more about fertilizing plants with organic fertilizers in this article.
Organic Fertilizer Advantages
Wide Range Of Nutrients
Organic fertilizers contain a lower absolute percentage of macronutrients than synthetic fertilizers, but they offer a much greater variety of elements.
This is important because plants evolved with high nutritional diversity and can utilize more than the 17 essential nutrients. A rich organic menu of nutrients allows the plant feed efficiently.
Organic Fertilizers Are Safe To Use
The expansive pallet of elements contained in organic fertilizers includes chemical buffers that help plants absorb nutrients. These buffers slow things down, avoiding overly rapid assimilation of nutrients and possible damage to the plant’s roots.
Another factor in slowing the absorption of organic fertilizers is the time needed for microbes to break down the material to make it accessible to plants. Note that some organic fertilizers like fish emulsion are more readily available to the plant.
For these reasons, it’s harder – but not impossible – to overdose your plants when using organic vs inorganic fertilizer.
Environmentally Sound
Organic fertilizers fit perfectly with the back-to-nature ethos of many modern gardeners. Organics are largely biodegradable and safe for the environment.
Furthermore, you don’t have to worry about unnaturally concentrated nutrients or corrosive chemical additives in your home.
Most organic products are sustainable, too – though some have questions attached. For example, peat moss has traditionally been harvested from ancient bogs, though steps have been taken in some areas to restore these lands after harvesting. Worker health in organic production is an issue for some products.
Despite these challenges, however, organic fertilizers are generally renewable and healthy for the ecosystem.
Organic Fertilizers Provide Microbial Sustenance
Like plants, microbes evolved to consume natural products: the rich diversity of organic material makes it an excellent food for soil organisms. In turn, a healthy microbial community benefits the soil by making it more fertile, friable, and nourishing to plants.
Though science hasn’t uncovered all the nutrients that make up a healthy soil ecosystem, we don’t need to know the details when using organics! Nature takes care of it.
Disadvantages of Organic Fertilizers
Weaker in Macronutrients
Organic fertilizers contain a much lower concentration of macronutrients – the very elements plants use most. Instead of a beefy synthetic NPK ratio like 20-10-10, an organic formula produces lower counts like 2-1-1. This simply means that given the same volume or weight of organic and inorganic fertilizer, the organic fertilizer will normally contain fewer nutrients.
This isn’t necessarily a big disadvantage – it just means you need to use more organic fertilizer to achieve the same result compared to inorganic fertilizer. Synthetic fertilizer was created for agriculture rather than houseplants: fast-growing vegetables consume more macronutrients than a slow-growing Peperomia.
Organic Fertilizers Are Often More Expensive
Organic fertilizers are more costly than synthetics; sometimes, significantly so. Because organic matter is grown and harvested and prepared rather than manufactured, its production doesn’t benefit much from economies of scale.
Also, since organic fertilizers provide a relatively small percentage of macronutrients, you may need more if it’s your only fertilization method.
This extra expense is balanced by the fact a potted plant doesn’t need a lot of fertilizer. While organic formulas may be pricey when compared to a manufactured inorganic brand, this becomes less significant considering how long they last.
Unsavory Properties
Let’s just get it out there: one of the challenges of organic fertilizer is getting used to it. Fish emulsion smells like the rotten fish juice it is. Compost gets everywhere and stinks. Even if properly seasoned manure isn’t really offensive, it still lacks an attractive cachet.
Many gardeners couldn’t care less, but other residents in their home may not favor a seaweed cologne. On the plus side, the scent dissipates in time – and you’ll get more used to it. Though it may seem strange to you now, many growers even come to like the smell.
The organic fertilizer that seems to choke people up the most is fish emulsion. It’s wonderful plant food but quite … distinctive. It is less eye-watering if well diluted, though two tablespoons per gallon of water is standard practice. Open a window.
Nutrient Content Of Organic Fertilizers Is Less Quantifiable
Unlike manufactured fertilizer, the chemical profile and amounts of each nutrient in organic material is approximated. Its components are less strictly quantifiable.
This fuzzy area allows organic producers some latitude for making claims on their labels, so seek reputable sources. Some growers make their own organic fertilizer despite the effort because it provides assurance.
The occasions when the less-precise nature of organic fertilizers might make a difference are when following a strict feeding regimen or addressing a specific deficiency.
Organic Fertilizers Are Harder To Store
Some organic fertilizers come in a handy bottle, but manure, compost, bone meal and suchlike are bulky and messy to use. Also, you often need more of them than you would a concentrated fertilizer – it’s inconvenient to stash a bag of manure under the sink.
Additionally, organic products are more prone to spoilage than dry manufactured formulas. Lastly, their delicious aroma attracts pests and animals, so organics must be stored in a secure location.
Organic Vs Inorganic Fertilizer – Decision Time
You don’t have to choose between manufactured or all-natural products! Now that you know the benefits – and limitations – of each type, you can find your own fertilizing strategy.
For example, using organic amendments to prepare the soil along with timely additions of a dilute synthetic fertilizer can produce beautiful, healthy results. Some growers substitute in kelp or fish products. You can judiciously mix the categories to suit your situation: your plants won’t mind!
If you’d like to learn more about fertilizing and growing healthy houseplants, check out some of the articles listed below, or take a look at my book, “Houseplants Made Easy”.