Fertilizers are any substance added to soil to supply nutrients and promote plant growth. They can be organic or inorganic, natural or synthetic. Organic fertilizers are sourced from naturally available materials while chemical or synthetic fertilizers are manufactured from synthetic chemicals. Organic fertilizers come from living organisms such as composted leaves and dried seeds, and animal by-products including bones, blood, and aged manure.
Organic fertilizers work together with soil microbes to release the most essential macronutrients nitrogen (N), phosphorus (P), and potassium (K) at a slow and steady rate. The manufacturer provides the percentage per weight of these nutrients in the NPK ratio. Different plant types have different nutritional needs at varying levels of growth.
These fertilizers have many other benefits too depending on the nutritional content, the type of plants, and the soil quality. However, note that they give off unpleasant odors since they are derived from dead plants and animal products.
Summary of the Best Organic Fertilizers
| IMAGE | PRODUCT | |
|---|---|---|
Best All-Purpose  |
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Best Starter  |
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Best Soil Builder  |
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Best for Tomatoes and Vegetables: Dr. Earth Tomato, Vegetable & Herb Fertilizer  |
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Best for Flowers  |
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Best for Potted Plants  |
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Reviews of the Best Organic Fertilizers
Best All-Purpose: Jobe’s Organics 09524 All-Purpose Granular Fertilizer
Jobe’s Organics offers all-natural fertilizers and potting soil for organic gardening. For many different kinds of plants, this all-purpose granular fertilizer provides a balance of NPK nutrients (at a 4-4-4 ratio). This organic fertilizer is made from feather meal, bone meal, processed poultry manure, and potassium sulfate. Jobe’s proprietary Biozome also includes a blend of beneficial microorganisms Archaea, bacteria, and mycorrhizal fungi.
This all-purpose organic fertilizer helps produce healthy plants including flowers, vegetables, shrubs, and trees. The included microbes are an essential component for this fast transfer of nutrients from the soil to plants. Archaea can help clean the soil and break down minerals into nutrients that plants can easily absorb.
Mycorrhizal fungi expand the root’s surface area, allowing plants to absorb more water and nutrients from the soil. They also increase plant resistance to stress. Furthermore, healthy bacteria improve soil structure. Overall, the Biozome microbes enhance soil health, promote plant growth, increase root mass, and help protect your plants against disease, drought, and pests.
Note that this product produces undesirable smells when used. To reduce the odors, mix it thoroughly with the soil before planting instead of applying it only on the soil surface. Also be reminded that the included microorganisms are healthy for outdoor gardens but may introduce fungus when used indoors.
Pros
• Fast-acting granular-style fertilizer
• Enhanced with proprietary microorganisms
• Effective on a variety of plants including vegetables, flowers, trees, and shrubs
• Can be applied less often than liquid fertilizer
Cons
• Strong smell
• May cause fungus growth indoors
Best Starter: Espoma Organic Bio-Tone Starter Plus
If you’re only starting to plant seeds or transplant them into the garden or pots, then you can use a starter fertilizer. Espoma is another reliable brand when it comes to organic gardening. The Espoma Bio-tone Starter Plus offers a good balance of NPK with 4-3-3 ratio. Use it to establish deep roots for any type of plants, new or transplanted.
This all-natural starter plant food is enhanced with beneficial bacteria and mycorrhizae. It works naturally within the soil to promote quick growth of larger root systems, prevent transplant loss, promote bigger blooms, and improve soil structure.
Mix the fertilizer into the top of the soil before planting. You can use it on the plant nursery, flower beds, or potted plants, in combination with other organic fertilizer options to supply more nutrients.
It’s very easy to use and customers have hardly any complaints, except for a few instances of mold or pest infestation, which can happen with any organic fertilizer. The easy solution is to mix it into the soil.
Pros
• Guarantees healthy young plants
• Reduces transplant loss
• Enhanced with helpful bacteria and fungi
Cons
• May encourage infestation
Best Soil Builder: Wiggle Worm Soil Builder
Soil builders are a natural, carbon-based food source for soil microbes to promote aeration of the soil. The Wiggle Worm Soil Builder is an all-natural fertilizer made purely of worm castings without any filler such as wood chips. Earthworm castings (also called vermicast) are basically earthworm wastes. They are an ideal soil builder that promotes plant growth and improves soil quality.
Worm castings are produced by feeding worms with organic material rich in a variety of minerals. As the worms digest these minerals and trace elements, they are altered chemically and physically into an all-natural soil amendment. The tiny football-shaped product helps improve the soil aeration since they are loose. It also includes a diversity of soil microbes that promote root development and boost plant health.
Soil builder worm castings also improve soil drainage to prevent the roots from becoming waterlogged or developing root rot. Adding vermicast to your garden soil also increases its water retention capacity as it contains organic matter that absorbs water at only the amount needed by the roots. Its loose shape lets the extra water slip through and drain easily.
The Wiggle Worm Soil Builder worm castings are an odorless, non-burning, and nutrient-rich fertilizer suitable for any organic garden. It is ideal for indoor or outdoor use, in potted plants, flowers, vegetables, and trees. It’s a cost-effective and long-term solution to enrich the soil’s biodiversity and help plants to absorb nutrients. One 30-pound pack can go a long way. Simply apply on the soil surface every two months during the growing season, or mix it with potting soil before planting or repotting.
Pros
• All-natural earthworm castings are ideal for any plant
• Can provide long-term nutrients
• Helps improve soil aeration and water retention
Cons
• Natural products are prone to infestation
Best Liquid: Neptune’s Harvest Organic Hydrolized Fish & Seaweed Fertilizer
Organic liquid fertilizers are a great supplement to plant nutrition during the critical growth stages of your crops. Neptune’s Harvest offers a liquid concentrate made from North Atlantic fish and seaweed at a 2-3-1 NPK ratio. It’s ideal for most types of plants, flowers, vegetables, and shrubs, either indoors or outdoors.
The high amount of phosphorus enhances root growth, as well as flower and fruit development. The combination of fish and seaweed can help build natural sugars in plants, resulting in plentiful, fragrant blooms and vibrant, healthy foliage. Simply dilute the concentrate with water while following the application rates on the label directions depending on your plant needs, then apply it to the root areas until the soil is saturated or spray it onto the plants.
We remind you to be extra careful when diluting this product. This concentrated fish and seaweed fertilizer has a stinky (composted fish!) smell straight from the bottle, so it’s best to handle it with gloves, outdoors, when mixing with water. Once diluted, the odor will fade even when applied indoors. Pets may also sniff around the areas of application, so best keep them away.
Pros
• Can be sprayed or watered directly
• Works well on a variety of plants
• Indefinite shelf life
• Excellent results on different plants
Cons
• Must be mixed at each use, not stored when diluted
• Powerful fishy odor in concentrated form
Best for Tomatoes and Vegetables: Dr. Earth Tomato, Vegetable & Herb Fertilizer
Tomatoes and vegetable plants consume nutrients at a quick rate and need a supplement of the essential elements. The Dr. Earth Tomato, Vegetable & Herb Fertilizer is formulated to supply plenty of nutrients with NPK ratio of 4-6-3 ratio, along with 7.5 percent calcium necessary for tomatoes and vegetables. Dr. Earth TruBiotic soil also includes beneficial microbes and mycorrhizal fungi to help improve soil structure and enhance nutrient absorption capacity in your vegetable garden.
This organic fertilizer is made from nutrient-rich natural fertilizers including bone meal, alfalfa meal, fish meal, potassium sulphate, and rock phosphate. High calcium content prevents nutrient deficiency blossom end rot where your tomatoes or peppers look perfect on top but black and soaked on the end. This OMRI-certified organic fertilizer is ideal for new plantings, transplants, or potted plants. You can add it to the soil before planting, during repotting, or as a top dressing or fertilizer tea at two-month intervals during growing seasons.
It’s very easy to use and is excellent for a variety of vegetables, but like any organic fertilizer, the unpleasant smell can be a problem when used indoors. A few users have also experienced bug infestation after using the product.
Pros
• High nutrient content ideal for tomatoes and vegetables
• Yields bountiful, healthy crops
• Excellent for use throughout the season
Cons
• Unpleasant smell if used indoors
• Prone to bug infestation
Best for Flowers: Down to Earth Rose & Flower Fertilizer
Flowering plants require a higher concentration of phosphorus which is responsible for fruit and flower development. The Down To Earth Rose & Flower Mix is an all-natural fertilizer that provides 4-8-4 NPK and magnesium derived from organic materials including blood meal, alfalfa meal, seabird guano, and rock phosphate which are rich in phosphorus. This fertilizer blend provides the necessary nitrogen for root and stem growth, high levels of phosphorus for bountiful, long-lasting blooms, and potassium for healthy roots.
This OMRI-listed granular fertilizer is great for edible bulbs, like garlic and onion, roses, and perennials. Apply the necessary amount to the soil when planting in a vegetable garden, flower beds, or containers, and use once or twice a month throughout the growing season. Mix into the top of the soil as instructed, either for new plantings or established plants. Repeat application when your roses or perennials start to bloom.
It is easy to use and works excellently as advertised. There are very few negative reviews, most of the complaints concerning the smell and attraction to bugs, which is normal for any natural fertilizer.
Pros
• High phosphorus content ideal for flowering plants
• Produces beautiful flowers
• Excellent for use throughout the season
Cons
• Unpleasant smell if used indoors
• Prone to bug infestation
Best for Potted Plants: Jobe’s Organics All-Purpose Fertilizer Spikes
Potted plants and hanging baskets also need additional nutrients from organic fertilizers. However, over feeding your houseplants can decrease growth and make them more vulnerable to pests and diseases. Jobe’s fertilizer spikes for potted plants are formulated with a balanced nutritional content, at a 4-4-4 ratio similar to Jobe’s organic all-purpose granular fertilizer. These pre-measured spikes make it easy to fertilize potted plants without having to mix anything with the soil.
Each fertilizer spike provides a slow and steady release of nutrients to the roots. Soil microbes break down the organic fertilizer into nutrients readily available for the plants. A single spike can feed your houseplant for the entire season without any chemical runoff. Simply insert the number of spikes recommended for the pot or box size. Make sure they are fully buried under the soil near the roots to prevent mold growth on the soil surface.
You can use the spikes for indoor or outdoor pots or in planting beds. Although, for houseplants, using whole spikes may be too much and cause burning of leaves. Be sure to use just the right amount of fertilizer for any plant.
Pros
• Small enough to bury into the soil around most plants
• Slowly releases nutrients throughout the season
• Odorless for indoor use
Cons
• Using a whole spike may burn plants
• The scent may attract dogs
Types of Organic Fertilizers
When choosing an organic fertilizer for your garden, it’s important to know the right type for your crops. Some fertilizers contain plant-based or animal-based materials, or a combination of both. Others may include naturally sourced minerals. The type of fertilizer is an essential factor because the ingredients used to make it impact the nutritional value.
Plant-Based
Plant-based organic fertilizers include products created using compost, alfalfa meal, cottonseed meal, soybean meal, and kelp or seaweed. This type of fertilizer breaks down quicker than others, but most of them provide lower nutrient levels (cottonseed meal and soybean meal offer up to 7% nitrogen).
Plant-based fertilizers are a good source of soil-essential carbon and enzymes that promote natural plant growth. Although typically low on the three common macronutrients (nitrogen, phosphorous, potassium, or NPK) they make excellent soil conditioners. They also help add drainage and water retention to the soil.
Animal-Based
Animal-based fertilizers are made from organic matter such as composted manure, blood meal, bone meal, and fish meal. Compared to plant-based fertilizers, this type offers considerably higher levels of NPK (specifically, nitrogen) and other nutrients.
These fertilizers are created with waste from meat and fish processing. Composted animal manures provide organic matter but few nutrients. Blood meal comes from the blood of slaughtered animals and bone meal is created from fish bones. Both usually come in powdered form. Fish emulsion is a liquid fertilizer made from processed fish remains. These fertilizers are high in many nutrients but usually give unpleasant smells and may attract pets and rodents.
Mineral-Based
Naturally available fertilizers such as rock phosphate and greensand are actually mined, which may be unsustainable. Technically, mineral fertilizers are not organic as they don’t contain carbon, but they can be used in combination with organic fertilizers. They can provide trace elements not found in organic fertilizers as well as essential nutritional components in higher concentrations than other naturally sourced materials.
In particular, rock phosphate mined from clay deposits is a natural source of phosphorus. It contains about 4 percent phosphorus along with high levels of calcium and traces of macronutrients nitrogen, potassium, and iron, magnesium, copper, manganese, and boron. Also, greensand is a green compound from sandstone mined from anoxic (oxygen-depleted) marine environments. It contains about 3 percent potassium as well as many trace minerals, like iron, magnesium, and calcium.
What to Consider When Choosing the Best Organic Fertilizer
Before you buy and apply organic fertilizers to your garden, you must know what to look for depending on the crops you cultivate. Choose a product that can provide the essential macro and micronutrients your plants need throughout the growing season, as well as other benefits that can improve the soil structure.
Organic Certification
Anyone can say a fertilizer is “organic” so you need to be extra careful and make sure the product is registered with the Organic Materials Review Institute or OMRI. Being OMRI listed means the product has been certified by the independent, nonprofit organization to successfully comply with USDA organic farming requirements. Always look for this label to make sure the fertilizer is safe for organic gardening. In the USA and Canada, you can look up a product in the OMRI database to check if it’s certified organic.
Liquid vs. Dry Fertilizer
Organic fertilizers come in granular or powdered form and liquid form. Dry fertilizer takes longer to break down while the liquid type dilutes with water for quick absorption. Many growers use both types at different stages of plant growth, but make sure you don’t use too much. Too much fertilizer, whether organic or synthetic, can contaminate water supplies.
For best results, dry organic fertilizers must be worked into the soil to allow microbes to break down the nutrients so they can be easily absorbed by plants. Use these granular fertilizers before or at the time of planting to provide nutitional value at a slow and steady pace throughout the growing season.
On the other hand, liquid organic fertilizers provide a quick-feed solution for growing plants. It usually comes in a thick, concentrated liquid form that you must dilute with water. Use a liquid fertilizer to give your plants a quick nutrient boost when it’s most needed in the season. Mix at half strength for young seedlings, and at full strength for when plants start to bloom or set fruit.
Nutrients
Different plants have different needs, but the three most essential nutrients plants need in the highest quantities are nitrogen (N), phosphorus (P), and potassium (K). The amounts of these elements present in the product must be indicated by the manufacturer on the package in a ratio of N-P-K representing the percentages by the total weight.
Nitrogen is necessary for plant growth as it is important in producing amino acids which are building blocks of plant proteins. It is also present in chlorophyll, which creates the green color in leaves.
Phosphorus is vital in enhancing the plant’s ability to store and use energy, especially during the process of photosynthesis. This element is essential in promoting root development, as well as flowering and fruiting.
Lastly, potassium is vital for the regulation of plant growth and encouraging deep roots, strong stems, and well-developed fruits and flowers.
Fertilizers also contain micronutrients including boron (B), zinc (Zn), manganese (Mn), iron (Fe), copper (Cu), and magnesium (Mg) in smaller quantities to promote plant development. Look for micronutrient contents on the back label of the fertilizer package.
Organic fertilizers may also include necessary bacteria and fungi cultures to improve the efficacy of the fertilizer and enrich the soil. As a side effect of using organic fertilizer, you may notice fungal growth on the surface as well as worms and insects in the soil, which are usually not bad for plants.
The Best Traditional Natural Plant Foods
Natural fertilizers take some time to break down and they are ideally added to the soil a few months before planting. If you don’t want to purchase commercial fertilizers, here are a few natural sources traditionally used as fertilizers.
Compost releases nutrients slowly and helps the soil retain moisture. You can put your kitchen scraps to use by making your own compost for your garden. Some common food waste you can add to your homemade compost includes coffee grounds, eggshells, and fruit peelings. Soaked coffee grounds are good for plants that thrive in acidic soil, such as blueberries, roses, and tomatoes. For plants that don’t like acid, add crushed eggshells, which are a good source of calcium. Lastly, fruit peels are rich in nutrients necessary for plant growth, like nitrogen from orange peels, and potassium from banana peels.
Bone Meal is created by pulverizing animal bones in slaughterhouses, which means it’s not a vegan option. You can also make your own bone meal at home by grinding bone scraps. Bone meal is an excellent source of phosphorus as well as calcium and other trace elements.
You can also use your garden waste to fertilize your plants naturally. Grass clippings and weeds from your garden or lawn are rich in nitrogen and make excellent fertilizers. Fallen leaves are also high in nutrients and help retain soil moisture.
The Advantages of Using Organic Fertilizer
Organic fertilizers provide a natural source of nutrition that requires less effort from you. Although the desired result doesn’t come as quickly as artificial fertilizers, they provide a healthier environment overall. They support microbes, fungi, and other organisms beneficial for natural plant growth.
The slow release of nutrients allows for consistent assimilation at a rate that plants need. The necessary nutrients are supplied through a biological process involving microbes. This natural, steady release of plant food also avoids burning from overfertilization.
Organic fertilizers support a healthy and diverse soil ecosystem. Healthy soil includes microbes that break down organic matter into essential nutrients, as well as worms, insects, and other organisms that burrow through soil and provide aeration.
Organic material from these fertilizers also improves the structure of the soil so it is less likely to erode. It also acts as a buffer to help neutralize acidity or alkalinity and also enhances water and nutrient retention.
Tips for Using Organic Fertilizer
To get all the benefits of organic fertilizers, it’s vital to understand how they work. It will take some time for soil microbes to consume organic matter and release nutrients that the plants can readily absorb. During the growing season, it can take about two weeks to see results. But in cool weather, it may take up to six weeks on average.
After application, these natural fertilizers will continue to supply nutritional value to your crops throughout the whole season. You can start fertilizing at the same time you plant the seeds or two weeks before planting seedlings to allow the microbes within the soil to break down the nutrients and the soil to absorb them.
For best results, add the fertilizers to the top three to six inches of the soil. Different plants need a variety of nutrients in different levels at each stage of growth. You can use liquid fertilizer as a supplement to dry fertilizer to give a boost of nutrients when your crops need them, like when tomato plants bloom or when cabbage plants form heads.
Although organic fertilizers are generally less harmful, they still pose risks to children and pets if consumed in high concentrations. Dogs may sniff around for the scent of blood or bone meal, while cats are attracted to fish emulsion. Pets may dig into the soil where you have applied these fertilizers and disturb your plants. Avoid ingestion by working into the soil and applying the fertilizers at the root level. Keep unused fertilizers in a storage space safe from pets and rodents.
Lastly, different plants have different nutrient needs and thrive in varying levels of soil pH. Perform a soil test before planting and fertilizing to get the best results.
FAQs
What type of nutrient is the most important for plants?
Nitrogen is considered the most important for plants, as it is consumed in great amounts and the soil often lacks this element as it can quickly turn into gas. While nitrogen, phosphorus, and potassium are all essential macronutrients for healthy plant growth, you may need higher levels of nitrogen from an organic fertilizer since other nutrients remain in the soil for a longer period.
How do you apply organic fertilizers to plants?
Apply organic fertilizer by working into the soil before planting. Beneficial microbes within the soil will break down the nutrients from the fertilizer and release them into the soil for plants to use. You can also apply the fertilizer around the soil where your plants are growing.
Can you over-fertilize your plants with organic fertilizers?
Just like with any type of fertilizer, it’s possible to over-fertilize your plants with organic fertilizers. Although the organic type can prevent burning, you may still face problems including excess nutrients if you don’t use the right fertilizer.
