Do You Know All Fertilizers For Your Plants? Full List

When you are in the nursery, are you confused by all of the options available? There are over thirty different fertilizers out there, each with their own unique properties and benefits. What are they, and which one do you use?

Fertilizers are soil additives that provide chemicals required for plant growth. Most fertilizers contain one or more of potassium, phosphorus, and nitrogen. Their specific ratio (called the N-P-K ratio) varies greatly among the 30 most common fertilizers:

Ammonium Nitrate34-0-0
Ammonium Sulfate21-0-0
Calcium Nitrate15.5-0-0
Diammonium Phosphate18-46-0
Monoammonium Phosphate11-48-0
Triple Super Phosphate0-46-0
Potassium Nitrate13-0-44
Potassium Chloride0-0-60
Blood Meal12-0-0

*These grades are indicative only as individual products will vary

This article will provide you with information about all of the fertilizers available. Read on to find out which ones you could or should not use for your potted plants.

What is a Fertilizer?

As outlined by the University of Tennessee, plants need around 18 different nutrients to complete their growing cycle. It can be challenging to find soil which this perfect blend of nutrients for your plant, and even then, as the plant grows, these chemicals are depleted due to use and decay. A fertilizer is any material that is added to the soil to replenish and enhance the chemical composition to make it more supportive of plant growth. The three essential plant nutrients are nitrogen, phosphorus, and potassium, and most fertilizers contain a combination of these three chemicals.

N-P-K Grade

The fertilizers you buy will likely show an N-P-K Grade on the product label. This shows the ratios of nitrogen (N), phosphorous (P), and potassium (K). For example, Potassium Nitrate (also called Saltpeter) has an N-P-K Grade of 13-0-44. This means that it has 13 percent nitrogen, no phosphorous, and 44% of potassium.

Organic vs. Inorganic Fertilizers

The main difference between fertilizers is whether these nutrients are delivered in organic or inorganic forms. Oregon State University explains that organic fertilizers are those that are made from either plant or animal sources.

The most popular organic fertilizers are compost, manure, or bone meal. Organic fertilizers usually hold a wide range of nutrients in small concentrations. Inorganic fertilizers are also called synthetic or commercial fertilizers, as they are man-made and manufactured substances.

They generally contain only a few nutrients, and most well-known synthetic fertilizers are ammonium phosphate or ammonium sulfate.

Fast vs. Slow Release Fertilizers

The other main difference between fertilizers is whether they are fast or slow release. Fast-release fertilizers are soluble in water and are quickly available for plant use. In contrast, slow-release fertilizers require a process to break down the material and release the nutrients. This process could be a fertilizer reaction with water or a microbial activity occurring within the fertilizer, for more check what the University of Arizona has to say.

While fast-release fertilizers can provide rapid assistance to needy plants, it is relatively easy to over-fertilize and create a soil condition unfavorable to the plant. For this reason, greater caution must be practiced with the application of fast-release fertilizers.

Many variables will affect how quickly the fertilizer is used by the soil and how often you need to reapply. In general, though, fast release fertilizers will likely need reapplication within two to four weeks. Slow-release products last longer usually required reapplication in approximately six to eight weeks.

Do You Know These 30 Fertilizers?

Now that you understand the critical characteristics of fertilizers, let’s dive in and find out more about the wide variety of organic and synthetic options in the market.


What is Urea?

Urea is a chemical present in the body of animals and used to metabolize nitrogen-containing compounds. It is found naturally in animal manure but is also produced synthetically. Urea is the most commonly used fertilizer for nitrogen, as it has the highest nitrogen content per unit (46%).

How is it sold?

Urea is sold in many forms, including as prills (solid globules), granules, pellets, crystals, and solutions. It can be purchased as granules in small 1lb (0.45 kg) bags, 10lb (4.5 kg) bags, or 45lb (20 kg) pails and can be sourced from Amazon here.

N-P-K Grade

Urea has an NPK grade of 46-0-0, as discussed here.

Is it suitable for indoor gardening?

Urea is suitable for indoor gardening; it has no color, odor, and is non-toxic. However, care must be taken to mix urea into the soil quickly after application; otherwise, it can react with the air and produce ammonia gas. Ammonia gas can irritate the eyes, skin, and respiratory tract. Care should be used to minimize skin contact and breathing in urea when applying it to the soil.

Is Urea Organic?

There are both organic and manufactured forms of urea available.

Ammonium Nitrate

What is Ammonium Nitrate?

Ammonium Nitrate is a compound of ammonia, salt, and nitric acid. It occurs naturally as a mineral salt, however now most Ammonium Nitrate is made synthetically and can be produced as a solid, liquid, or gas.

While it has a lower nitrogen content than urea (34%), it is also less reactive classing Ammonium Nitrate as a relatively stable fertilizer. However, with heat and pressure, it becomes an explosive substance.

How is it sold?

Due to security concerns, Ammonium Nitrate is not sold or available as a retail product. Government regulations have been imposed, meaning only commercial farming and agriculture businesses can obtain it, and then only under license.

N-P-K Grade

Ammonium Nitrate has an NPK grade of 34-0-0, as discussed by Smart Fertilizers.

Is it suitable for indoor gardening?

While Ammonium Nitrate is stable and suitable for indoor gardening purposes, as mentioned above, it is only available under license for commercial agriculture businesses.

Is Ammonium Nitrate Organic?

Ammonium Nitrate can be found in organic forms (as natural mineral salt) or synthetic one.

Ammonium Sulfate

What is Ammonium Sulfate?

Ammonium Sulfate (also called Sulfate of Ammonia) is a compound of ammonia and sulphuric acid. While it occurs naturally in the mineral, mascagnite is now made synthetically. This because it is rare to find in mineral form. It is an odorless and almost colorless crystal salt which is highly soluble in water.

This makes it a ready source of nutrients for plants; however, Ammonium Sulfate is lower in Nitrogen than Ammonium Nitrate (21%). The presence of sulfur (24%) works to increase the acidity (lower the Ph) of the soil and so it is recommended for alkaline soils.

How is it sold?

It is sold in crystal form in 4lb (1.8 kg) with a good quality one available on Amazon here.

N-P-K Grade

Ammonium Sulfate has an NPK grade of 21-0-0, as discussed by the manufacture.

Is it suitable for indoor gardening?

Ammonia Sulfate is suitable for indoor gardening as it is non-toxic, available in small quantities. The sulfur content makes it especially useful for leafy plants such as herbs.

Is Ammonium Sulfate Organic?

Ammonium Sulfate does exist in organic form. However, due to the rare natural form of Ammonium Sulfate (the mineral mascagnite), it is mostly available in synthetic form.

Calcium Nitrate

What is Calcium Nitrate?

Calcium Nitrate is a synthetic compound made by applying nitric acid to limestone and then neutralizing it with ammonia. It has an appearance like salt and is the only water-soluble form of calcium. This makes it invaluable as both a fertilizer and treatment for plant diseases resulting from calcium deficiency.

How is it sold?

Calcium Nitrate is sold in granular form in smaller quantities of 1lb (0.5 kg) up to 5lb (2.3 kg). There are some excellent sources of Calcium Nitrate available through Walmart here.

N-P-K Grade

Calcium Nitrate has an NPK grade of 15.5-0-0 with 19% Calcium, as discussed here.

Is it suitable for indoor gardening?

Calcium Nitrate is suitable for indoor gardening as it is non-toxic and is available in small quantities. Moreover, the best way to apply Calcium Nitrate is as a foliar spray, making it very suitable to treat house plants.

Is Calcium Nitrate Organic?

Calcium Nitrate is not organic. It is only available in a synthetic form.

Diammonium Phosphate

What is Diammonium Phosphate?

Diammonium Phosphate (DAP) is one of the most commonly used dry phosphorous based fertilizers on the market. It is manufactured by combining ammonia and phosphoric acid. Similar to the other manufactured fertilizers, it is highly soluble.

Therefore the nutrients in this fertilizer are readily available to the plants. As outlined by Michigan State University, because of the acidic nature of its ingredients, Diammonium Phosphate has an acidic effect on the soil.

How is it sold?

DAP is sold as granules or soluble powder. It can be purchased in small lots of 1lb (0.5 kg) and 2lb. It is available online at Walmart here.

N-P-K Grade

The NPK grade of DAP is 18-46-0, as discussed by Michigan State University.

Is it suitable for indoor gardening?

DAP is suitable for indoor gardening, with the caution to make sure recommended dilutions are followed. Too much DAP can burn the plants. Also, it is advised not to use in pots where seeds will be grown as it can damage the seeds.

Is Diammonium Phosphate Organic?

DAP is not organic. It is only available in the manufactured form.

Monoammonium Phosphate

What is Monoammonium Phosphate?

Monoammonium Phosphate (MAP) is very similar to DAP, except that there is less ammonium present. For this reason, it is slightly less acidic than DAP. MAP also has a higher phosphorus content than DAP, and so is suitable for blooming plants, including fruits and vegetables. As outlined by Michigan State University, in all other respects, MAP has precisely the same effects on the soils and plants as DAP.

How is it sold?

MAP is sold in granular form in 10lb (4.5 kg) bags and can be purchased online from Walmart.

N-P-K Grade

MAP has an NPK Grade of 11-48-0, as discussed here.

Is it suitable for indoor gardening?

As per DAP, MAP is suitable for indoor gardening.

Is Diammonium Phosphate Organic?

MAP is not organic. It is only available in manufactured form.

Triple Super Phosphate

What is Triple Super Phosphate?

Triple Super Phosphate (TSP) is produced by treating phosphate rock with phosphoric acid. As a result, it is a concentrated form of phosphorous. More precisely it is the highest content of phosphorous in dry fertilizers that do not contain nitrogen. It is water-soluble, so it is readily available for plant use.

How is it sold?

TSP is sold in 4lb (1.8 kg) bags of soluble granules with a good quality one from Amazon.

N-P-K Grade

TSP has an NPK Grade of 0-46-0, as discussed by the Michigan State University.

Is it suitable for indoor gardening?

While TSP is suitable for indoor gardening, this fertilizer is best for flowers, fruit trees, and shrubs. Therefore, it may not be relevant to the type of plants you are growing in your house.

Is Triple Super Phosphate Organic?

TSP is not organic, as it is a synthetic fertilizer.

Potassium Nitrate

What is Potassium Nitrate?

Potassium Nitrate, traditionally called Saltpeter, has been used as a fertilizer since the early Roman and Greek times. It is a compound of two nutrients essential for plant health being Nitrogen and Potassium. Potassium Nitrate is found naturally in cave deposits and in deserts. Still, most are now manufactured due to the decreased costs involved.

How is it sold?

Potassium Nitrate is sold in 4lb (1.8 kg) bags of soluble crystals with a good quality one available from Amazon here. Please note that due to some security concerns with Potassium Nitrate, valid identification may be required for purchase.

N-P-K Grade

Potassium Nitrate has an NPK Grade of 13-0-44.

Is it suitable for indoor gardening?

It can be used for indoor plants, but best only for those who have a dormant period such as perennial herbs. Potassium is a beneficial substance to help these plants build up their reserves for the dormant period.

Is Potassium Nitrate Organic?

While Potassium Nitrate is found in natural forms, the typical form is synthetic.

Potassium Chloride

What is Potassium Chloride?

Potassium Chloride is one of the highest sources of potassium. It is also known as muriate of potash (MOP). It is a transparent crystal readily dissolvable in water, making it a fast release option when potassium supplementation is required for the soil.

How is it sold?

Potassium Chloride can be purchased in 4lb (1.8 kg) bags of soluble crystals.

N-P-K Grade

Potassium Chloride has an NPK Grade of 0-0-60, as discussed here.

Is it suitable for indoor gardening?

While Potassium Chloride can be used indoors, the potassium content is best suited for growing potatoes and root vegetables such as carrots and parsnip. For this reason, Potassium Chloride may not be useful for your indoor garden.

Is Potassium Chloride Organic?

Potassium chloride does occur in nature solely as the mineral sylvite or combined with other minerals in ocean water and brine. However, there are also synthetic forms available. So, it is best to check the fertilizer label to determine whether it is organic or synthetic.

Blood Meal

What is Blood Meal?

Blood meal is a dry, inert powder made from blood and used as both an organic fertilizer and a high protein animal feed. It is one of the highest organic sources of nitrogen and promotes rapid vegetative growth.

How is it sold?

Blood meal is available in a range of sizes from 3lb (1.5kg) to 8lb (4kg) through Amazon here.

N-P-K Grade

The NPK grade for blood meal is generally 12-0-0.

Is it suitable for indoor gardening?

Blood meal is suitable for indoor gardening but in only minimal amounts. As suggested by the Penn State University, it can be added into commercial potting mixes, or used as a critical ingredient in making your oil soil mix. However, the high level of nitrogen should be used sparingly to avoid putting too much nitrogen into the soil.

As bone meal is a substance derived from animals, it also has a powerful smell that some people may find uncomfortable. So it would be best to test this product in an outdoor planter first before bringing it inside.

Is Blood Meal Organic?

Blood Meal is organic, being an all-natural fertilizer.

Bone Meal

What is Bone Meal?

Bone meal is a powder made from ground-up animal bones, usually beef bones. Similar to blood meal, it is a by-product of the animal slaughter process. It is a slow-release fertilizer, putting phosphorous into the soil for up to four months. Bone meal also contains calcium and is helpful for your flowering plants, including roses and bulbs.

How is it sold?

Bone meal is available online in quantities ranging from 3lb (1.5kh) to 20lb (9kg), with one highly recommended by over 700 users available from Amazon here.

N-P-K Grade

Bone meal can have an NPK grade up to 3-20-0, as discussed by Washington State University here.

Is it suitable for indoor gardening?

While bone meal delivers excellent nutrients for your flowering plants, it is known to smell bad, with some people likening it to a sewage smell. So, while technically there is no issue with indoor use, another source of nutrients is recommended to protect the comfort of your home environment.

Is Bone Meal Organic?

Blood Meal is organic, being a fertilizer made from all-natural ingredients.


What is Boron?

Boron is an element and a nutrient required for a plant to thrive through its complete lifecycle. It is known as a micronutrient because, as discussed by the University of Minnesota. However, it is an essential element, it is required in minimal amounts.

How is it sold?

As boron is only required in such small quantities, it is usually sold combined with other micronutrients such as iron, magnesium, and zinc in small 1lb (0.5kg) lots. One such product can be found on Amazon here.

N-P-K Grade

The NPK Grade for Boron is 0-0-0, as it is a pure element.

Is it suitable for indoor gardening?

Boron by itself is not generally used for indoor gardening, as the amounts required are usually contained within the potting mix you are using. If you are concerned about micronutrient deficiency, a combination can be added to the soil. This comes with a significant warning though for boron toxicity if too much is applied.

Is Boron Organic?

Boron is a natural element and, therefore, can be classed as organic.

Chelated Iron

What is Chelated iron?

Chelated Iron fertilizer is also known as sequestered iron. It is a soluble form of iron that can be used to promote healthy green leaves and to treat iron deficiency conditions such as Iron Chlorosis. As reported by the University of Florida, iron is essential for plant health. It cannot be directly added to the soil as it combines with other chemicals to form compounds that are not viable for use by the plant. Making a chelated form allows the iron to be dissolved in water and provided directly to the leaves.

How is it sold?

Chelated forms of iron are typically available in liquid form, combined with other micronutrients. It is available in 1 gallon (3.8L) bottles, such as those found on Amazon here.

N-P-K Grade

Iron is its own independent element, and so has an NPK Grade of 0-0-0.

Is it suitable for indoor gardening?

Chelated iron is safe, suitable, and easy to use for indoor gardening.

Is Chelated iron Organic?

Iron is a naturally occurring element, and so is also organic.

Compost Tea

What is Compost Tea?

Compost Tea is just as the name suggests – compost soaked in water. Compost is well known to provide the soil with beneficial microbes, and the tea becomes a diluted source of nutrients.

As a liquid, it can be sprayed on plant leaves or used to water with. As discussed by the University of Connecticut, real compost tea is ‘brewed’ under aerobic conditions (with oxygen). It is called actively aerated compost tea (AACT).

How is it sold?

Compost Tea is sold as either dry bags which are soaked in water, or as a ready-made liquid. Both are available online, and the liquid can be found in 1 Quart (approximately 1L) bottles on Amazon here.

N-P-K Grade

The NPK Grade of Compost Tea is 0.5-1-1. While the nitrogen, phosphorous, and potassium values may be relatively low, it is the microbes within the tea that provide benefit to the plants.

Is it suitable for indoor gardening?

Compost Tea is suitable for indoor gardening as it can be directly applied to individual plants.

Is Compost Tea Organic?

Compost Tea is organic as it includes only plant materials and rock powders.

Corn Gluten

What is Corn Gluten?

Corn Gluten is a by-product of corn milling and is a well-known, beneficial weed inhibitor and plant food. As outlined by Washington State University, it is a pre-emergent herbicide that prevents weeds from sprouting but is not effective on established weeds. It also has traces of nitrogen, which aids the overall health of the plant.

How is it sold?

Corn Gluten is sold in granule form as part of an overall weed prevention product or in a liquid spray for easier application. The spray comes in 1 Quart (approximately 1L) bottles and can be found online at Amazon here.

N-P-K Grade

Corn Gluten has an NPK Grade of 8-0-0, as discussed here.

Is it suitable for indoor gardening?

Corn Gluten is best known for its weed prevention properties. Therefore, while safe for indoor use, it may not be relevant to indoor gardens. Also, Corn Gluten is not a selective herbicide. It can stop the growth of not only weeds but also some species of flowers and vegetables. For these reasons, Corn Gluten would not be recommended as the best supplement for your indoor plants.

Is Corn Gluten Organic?

Yes. Corn gluten is derived from plants and so is classified as organic.

Cottonseed Meal

What is Cottonseed Meal?

Cottonseed meal is a by-product of cotton processing. The cotton is removed from seeds that are then pressed to extract the oil. The remainder of the cottonseed is ground into a meal. As described by the New Mexico State University, cottonseed meal is a slow-release fertilizer and tends to be slightly acidic. This makes it most suitable for flowering plants such as camellias and azaleas. This fertilizer is not suited to vegetables.

How is it sold?

Cottonseed Meal is sold in bags of 3lb (1.4kg) to 5lb (2.3kg) with a highly rated one found online through Amazon here.

N-P-K Grade

While different products will vary, as published by the University of Idaho, the average NPK Grade for Cottonseed Meal is 7-2.5-1.5.

Is it suitable for indoor gardening?

Yes. Cottonseed Meal is both safe and easy to use on indoor plants. It is especially suited to the acid-loving plants, such as the flowers outlined above.

Is Cottonseed Meal Organic?

Cottonseed Meal is an organic fertilizer as it is derived solely from plant material.

Epsom Salt

What is Epsom Salt?

Epsom salt is a salt formed from the combination of magnesium and sulfur. Its chemical name is Magnesium Sulphate and is needed in plants to support the production of chlorophyll along with many other growth processes. Epsom salts is a highly soluble form of magnesium used to treat magnesium deficiency, mostly in flowering plants, fruits, and vegetables.

How is it sold?

Epsom salt has many human and plant uses, making it easy to source through supermarkets and bulk wholefood stores. It can also be purchased online in 4lb (almost 2kg) lots, with some directly available from Amazon here.

N-P-K Grade

The NPK Grade for Epsom Salts is 0-0-0. It is the magnesium and sulfur in this fertilizer that is of most value.

Is it suitable for indoor gardening?

Epsom Salts is an excellent source of soluble magnesium and is safe for both plant and human use. However, as a metal, magnesium can build up in potted plants. As reported by Washington State University, if there is no deficiency, Epsom Salts may lead to an oversupply of magnesium and even damage to the plant. For indoor plants, a well-balanced fertilizer suitable for the type of plants you are growing should be sufficient.

Is Epsom Salt Organic?

Epsom salt can either be mined and sold in its natural form, which would make it organic. It can also be manufactured, resulting in a synthetic form of Epsom Salt available as well.

Fish Meal

What is Fish Meal?

Fish Meal is a by-product of the fishery industry and is from the dried and ground tissue of leftover fish cuttings. Sometimes the oil is removed from this waste, while other times, the fish oil remains in the meal.

Fish Meal is mostly used as a feed for poultry or pigs. It also provides a wonderful source of natural nitrogen and phosphorus for plants. In its powdered form, it is generally used as a soil amendment to boost the planting substrate’s health.

How is it sold?

Fish Meal is sold as fertilizer in loose powder form. It can be purchased online in 5lb (2.3kg) boxes, such as that available from Amazon here.

N-P-K Grade

As shown by Oregon State University, The NPK Grade of Fish Meal can be up to 10-6-0. Products readily available on the market have a slightly lower nitrogen content, having an NPK grade of 8-6-0, as shown here.

Is it suitable for indoor gardening?

Fish meal is undoubtedly safe for use indoors and can readily be added into the soil of potted plants. However, there are two factors to consider for indoor use: the suitability to indoor plants and the smell.

As a fertilizer, fish meal is the most appropriate heavy feeder like corn, tomatoes, and potatoes and is recommended for outdoor plants, flower beds, trees, and shrubs. Also, similar to bone meal, fish meal does smell. So for both of these reasons, it is not highly recommended as a fertilizer for indoor conditions.

Is Fish Meal Organic?

As Fish Meal is made from an animal source, it is classified as an organic fertilizer.

Green Sand

What is Greensand?

Greensand is a natural mineral harvested from ancient seabeds. As the seas declined and receded, they left behind a seabed full of marine nutrients that are now extracted and added to soil to improve the soil quality. It does this through the presence of the vital mineral called glauconite, which contains iron, potassium, and magnesium.

One of Greensand’s fundamental properties is its ability to absorb and hold water. So, it is used mostly to hold together loose and sandy soils and to break up clay soils. It is an incredibly slow-releasing additive, taking approximately four years to degrade from the soil.

How is it sold?

Greensand is sold as sand in 7.5lb (3.4kg) bags and is available online from Amazon here.

N-P-K Grade

As outlined by Oregon State University, depending on Greensand’s source, it can have an NPK Grade of up to 0-1.5-5. However the most readily available product on the market has an NPK grade of only 0-0-0.1.

Is it suitable for indoor gardening?

While it is possible to use Greensand to the soil of your indoor plants, it may be more useful to use a potting mix uniquely suited to the plants you are growing.

Is Greensand Organic?

Greensand is harvested from natural sources, and so is organic.


What is Guano?

Guano is the name given to excrement from either bats or seabirds. It is sourced from caves around bodies of water. It is harvested from areas with little precipitation, which would dilute the nutrients in the guano. The risk with guano is the transfer of diseases to the soil, but this is minimized by aging the product and subjecting it to decomposition activity from guano beetles.

How is it sold?

Both bat and seabird guano is available in bags ranging from 1.5lb (0.7kg) to 5lb (2.3kg). It can be sourced online from Amazon here.

N-P-K Grade

The NPK Grade will differ depending on the source, with bat guano having a rating of around 7-3-1 and seabird guano rating being 0-11-1. Bat guano more suitable for leafy plants as it is higher in nitrogen. Because of the higher phosphorous levels, seabird guano is better for fruit or seed plants.

Is it suitable for indoor gardening?

Guano is safe to use for indoor plants, but like any animal-based and excrement derived product, it may have a smell that could permeate your home. It is best to test any guano product outside before bringing into your home.

Is Guano Organic?

Yes, the guano is organic, as it comes from purely natural sources.


What is Humates?

As discussed by the University of Wisconsin, humates are the collective name for mineral organic matter extracted from decomposed organic matter such as coal or compost. These substances are treated with sodium hydroxide to dissolve the organic matter, which is then dried into humate, a black powder.

How is it sold?

Humates are sold as a soluble powder or in liquid form. The powder is soluble, sold in small quantities of around 7oz (200g), and can be found on Amazon here. The liquid can be purchased in 32ox (1kg) or 128oz (3.6kg) bottles and is located on Amazon here.

N-P-K Grade

Humates tend to have a high potassium content, with the general NPK ratio being 0-3-14.

Is it suitable for indoor gardening?

Humates are suitable and safe to use in indoor gardens.

Is Humates Organic?

Humates are extracted from decaying organic material, and so are classified as a natural fertilizer.


What is Kelp?

Kelp is the largest seaweed species, and as a product of the nutrient-rich ocean, it holds a wealth of both macro and micro-nutrients. As outlined by Washington State University, it is both a supplement for human nutrition and an organic soil conditioner to improve plants’ health.

How is it sold?

Kelp is sold in various forms, including raw, as a powder or meal, and as a liquid.

N-P-K Grade

As shown in the different kelp products here, there are slightly different NPK Grades depending on the form the kelp comes in. For example, as a powder, kelp is 1-0.1-2, whereas as a liquid, it is 0.5-0-0.5.

Is it suitable for indoor gardening?

Kelp is suitable for indoor gardening, but be mindful that it is advisable to keep it away from any pets due to the high arsenic content.

Is Kelp Organic?

Yes, kelp is made from natural ingredients and is therefore organic.


What is Manure?

Manure is animal excrement, usually from farm animals. Manure can be from dairy cows, horses, poultry, sheep, swine, or even more recently, llama manure has become available. It is sourced from vegetarian animals as their manure will include decomposing plant matter full of macro and micro-nutrients to assist with plant growth.

How is it sold?

You may likely be able to source bags of raw manure from local farms or stables. Otherwise, both chicken and cow manure can be purchased online in 3.75lb (1.7kg) and 5lb (2.3kg) bags from Amazon here. If higher quantities are required, you can find them from Walmart, which sells cow manure in 20lb (9kg) bags online or 50lb (23kg) bags.

N-P-K Grade

Is it suitable for indoor gardening?

While the nutrients in manure would be beneficial for indoor plants and safe to use, the smell makes manure contraindicated for indoor gardening.

Is Manure Organic?

Yes, manure is an organic fertilizer.


What is Milorganite?

Milorganite is a biosolid sludge which is a product from the sewage treatment and water purification process. It is named after the Milwaukee Metropolitan Sewerage District that developed it – MILwaukee ORGAnic NITrogEn. Milorganite is beneficial for a variety of plants but is best known as a slow-release fertilizer for lawns. As tested by the University of Georgia, it has been shown to be an effective repellant for deer and other foragers of grasses and crops.

How is it sold?

Milorganite is sold in bags ranging from 5lb (2.3kg) to 50lb (23kg) and is available online.

N-P-K Grade

This product has a relatively low nitrogen and phosphorous rating, with an NPK Grade of 6-2-0. However, Milorganite is very high in iron, being 15% of the composition.

Is it suitable for indoor gardening?

Milorganite can be used for indoor plants, but (as stated by the manufacturer), it can be smelly. So it is best to work into the top few inches of potting mix to help mask the smell.

Is Milorganite Organic?

Yes, Milorganite is organic as it is made of natural ingredients from the water reclamation process.


What is Miracid?

Miracid is a manufactured and trademark plant food name from the Miracle-Gro brand of gardening products. It is recommended for use on acid-loving plants such as rhododendrons, orchids, and azaleas. It is a mixture of ammonium and potassium phosphate, urea, potassium chloride, boric acid, sodium molybdate, zinc, iron, manganese, and copper.

How is it sold?

Miracid is sold in 4lb (1.8kg) bags and can be sourced online from Amazon here.

N-P-K Grade

The NPK Grade for Miracid is 30-10-10.

Is it suitable for indoor gardening?

The manufacturers recommend Miracid for indoor and outdoor use, with only a small amount required for indoor pots and around ½ teaspoon per gallon every two weeks.

Is Miracid Organic?

Many of the ingredients in Miracid are synthetic; therefore, it is not an organic fertilizer.


What is Osmocote?

Osmocote is a registered business name for a range of controlled-release fertilizers. There are Osmocote fertilizer products known as a classic, pro, plus, flower and vegetable, and nursery, all with their own unique ingredients and uses. In common, though, the nutrient prill is covered by a coating that opens and releases its nutrients as the soil temperature warms. Some of the ingredients include ammonium nitrate and phosphate, potassium and magnesium sulfate, iron phosphate, manganese sulfate, sodium molybdate, copper sulfate, and zinc oxide.

How is it sold?

Osmocote products are sold in bangs ranging from 1lb (0.5kg) to 50lb (23kg) bags and containers and can be purchased online.

N-P-K Grade

The NPK Grade of Osmocote products varies depending on the specific use of the fertilizer. For example, the Flower and Vegetable product has a ratio of 14-14-14, and the Pro version has an NPK Grade of 19-5-9.

Is it suitable for indoor gardening?

Osmocote products are suitable for use in indoor gardens.

Is Osmocote Organic?

Osmocote contains some synthetic elements and therefore, cannot be classified as organic.

Soybean Meal

What is Soybean Meal?

Soybean Meal is created from soybeans leftover from the oil extraction process. They are ground down into a coarse powder, high in protein and a source of nitrogen.

The meal is often used as food for pigs, cows, and chickens and can also be used to improve the soil’s nutrient quality.

How is it sold?

As Soybean Meal is sold as animal food, it may be purchased in bulk lots from feed supply stores. Smaller quantities can be bought online, such as the 5lb (2.3kg) boxes.

N-P-K Grade

The NPK Grade of Soybean Meal is 7-1-2.

Is it suitable for indoor gardening?

Soybean meal is suitable for indoor gardening.

Is Soybean Meal Organic?

Soybean Meal is made only from plant material and therefore is an organic fertilizer.


What is Sul-Po-Mag?

Sul-Po-Mag is the trade name for a mineral known as sulfate of potash-magnesia. Other names for this mineral are langbeinite and K-Mag. It is considered to be a highly economical source of potassium for organic growers. Still, as outlined by the University of Massachusetts, it should only be used when magnesium is also required. The potassium content makes Sul-Po-Mag specifically beneficial for fruiting plants.

How is it sold?

Sul-Po-Mag is sold as a water-soluble powder in bags ranging from 5lb (2.3kg) to 50lb (23kg). It can be purchased online.

N-P-K Grade

The NPK Grade for Sul-Po-Mag is 0-0-22, with 11% Magnesium and 22% Sulphur content.

Is it suitable for indoor gardening?

Yes, Sul-Po-Mag is suitable for indoor gardening, with just 1 Tablespoon required per gallon of soil in containers.

Is Sul-Po-Mag Meal Organic?

Yes, Sul-Po-Mag is derived from a naturally occurring mineral, and so is classed as an organic fertilizer.

Rot Stop

What is Rot Stop?

Rot Stop is a trading name for a product manufactured by Bonide. It is made from calcium chloride and it is used specifically to treat tomato blossom end rot caused by calcium deficiency.

How is it sold?

Rot Stop is sold in liquid form, either in 16oz (473ml) bottles or in a form ready to spray, which is 32oz (946ml). Both can be purchased online.

N-P-K Grade

Rot Stop does not provide any nitrogen, potassium, or phosphorous, so its NPK Grade is 0-0-0. However, it does have 9% calcium, an active ingredient to stop blossom rot on tomatoes.

Is it suitable for indoor gardening?

Rot Stop is suitable for use indoors but will only be relevant if you are growing tomatoes inside.

Is Rot Stop Organic?

No. Rot Stop is a manufactured fertilizer and therefore is not organic.

Wood Ash

What is Wood Ash?

Wood ash is a residue after the wood has been burnt. It is a good source of fast-acting potassium and helps neutralize acidic soil. However, specific physical and chemical characteristics of wood ash can greatly depend on the source of the wood with more information on this available from the University of Georgia here. This makes checking the specific properties of the wood ash you are purchasing very important.

How is it sold?

Wood ash can be purchased as a powder in 1 gallon (4.5L) bags. It can be sourced online from Amazon here.

N-P-K Grade

While the NPK Grade of wood ash can vary significantly across products, it is generally around 0-1-3, as outlined here. Calcium is the most abundant element in wood ash (around 15%), which assists in the neutralization of acidity in the soil.

Is it suitable for indoor gardening?

While wood ash can be used for indoor gardening, there are few dangers. The dust particles can disperse, causing respiratory tract symptoms, and the alkaline nature can irritate the skin.

Is Wood Ash Organic?

Yes, Wood Ash is an organic fertilizer.

Fertilizing Good Practice

Many of the fertilizers outlined in this article concentrate on providing the primary macronutrients for your potted plants, being nitrogen (N), phosphorus (P), and potassium (K). However, there are also secondary macronutrients required for plant health as well, being: magnesium (Mg), calcium (Ca), and sulfur (S).

Eight other elements are known as micronutrients, which are also essential for your plant’s thriving but are needed in much smaller amounts. These micronutrients are boron, chlorine, copper, iron, manganese, molybdenum, nickel, and zinc.

While there may be specific fertilizers to amend the acidity level of the soil or to address a particular mineral deficiency, a range of fertilizers will seek to deliver a broad spread of all the macro and micro-nutrients required for your plant. The message here is that while the macronutrients are vital, don’t forget the micro-nutrients of plant health.

Fertilizing Problems

Most of the fertilization problems come from over-fertilization and not knowing your soil. Check this fertilization guide for herbs if you want to know more. In a hurry? Here some quick takeaways:

  1. Do not fertilize in winter: during the colder months, many plants slow their growth and become ‘dormant’ during which fertilizer is not used and just accumulates into the soil damaging the plants.
  2. Fertilize more in summer: due to a higher temperature and more light, your indoor plants will grow, and therefore will need many more nutrients to support this growth.
  3. Don’t over-fertilize: If a little bit of fertilizer is good for the plant, then a lot must be even better. Wrong! Too much of either macro and micronutrients in the soil can create a toxic environment for your plant and interrupt its growth and normal functioning. Check this fertilization guide from some good practice when fertilizing. is part of the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites like mine to earn advertising fees by promoting good quality products. I may receive a small commission when you buy through links on my website.


A young Italian guy with a passion for growing edible herbs. After moving to the UK 6 years ago in a tiny flat, it was impossible to grow herbs outside. So I start my journey in growing indoor and so I decided to share my knowledge.

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