All plants need nourishment. In nature, plants cooperate with microorganisms like fungi and bacteria to scavenge nutrients from a variety of sources, including the organic and mineral content of the soil and gases in the atmosphere. Under cultivation, these systems are not as robust. Domestic plants, from lawn grass to houseplants, need a little help to grow their best. That’s where fertilizer comes in.
Organic fertilizers stimulate and support the natural processes plants use to feed themselves. The fertilizer feeds soil-dwelling microorganisms that then deliver the nutrients to plants. Over time, they increase soil organic matter which leads to improved soil aeration and water-holding capacity and a better physical growing environment.
The best organic fertilizer options have an optimal NPK ratio (percentage by volume of nitrogen, phosphorus, and potassium) for the plants to thrive. They’re derived from natural ingredients like plant scraps, animal waste, and minerals. Some are liquids, and others are dry. High-quality fertilizer requires minimal processing, is easy to apply, with a consistent texture throughout.
The best organic fertilizer makes edible or ornamental plants healthier, providing a balance of nutrients, quality ingredients, and an application method that suits the gardener. Below, learn tips on choosing the right kind for your plants, and to find out why the following fertilizers are top performers.
- BEST OVERALL: Jobe’s Organics 09524 Purpose Granular Fertilizer
- BEST LIQUID: Neptune’s Harvest Organic Hydrolized Fish & Seaweed
- BEST SLOW RELEASE: Jobe’s Organics All Purpose Fertilizer Spikes
- BEST SOIL BUILDER: Wiggle Worm Worm Castings Organic Fertilizer
Types of Organic Fertilizers
It’s important to choose the right type or combination of organic fertilizers for your garden. Some products may be entirely plant-based or animal-based. Others may include a combination of plant-, animal-, and mineral-based ingredients. It’s more than a matter of personal choice; these products actually serve different purposes.
Plant-based organic fertilizers include such products as compost, cottonseed meal, alfalfa meal, soybean meal, and seaweed. Although cottonseed meal and soybean meal each offer up to 7 percent nitrogen, most plant-based fertilizers offer lower nutrient levels.
This type of fertilizer is better known as sources of soil-improving carbon as well as enzymes and natural plant growth stimulants that aren’t found anywhere else. These products break down quickly and make excellent soil conditioners.
Animal-based fertilizers, such as blood meal, bone meal, and fish meal, deliver significantly higher levels of the vital macronutrients (nitrogen, phosphorus, and potassium) than their plant-based counterparts.
These fertilizers are made with waste materials of meat and fish processing facilities. Blood meal and bone meal are granular products that slowly release their nutrients throughout the growing season. Fish emulsion is typically used as a fast-acting liquid fertilizer.
Not all inorganic fertilizers are synthetics. Mineral fertilizers are not technically “organic” as they contain no carbon, but some are used as part of an organic fertility system. They are excellent sources of trace elements that may not be present in other fertilizers.
For instance, rock phosphate is a natural source of phosphorus that is mined from clay deposits. In addition to nearly 4 percent phosphorus, it contains high levels of calcium along with traces of nitrogen, potassium, magnesium, iron, manganese, copper, and boron.
Greensand is a type of sand or sandstone that is mined from shallow marine sediment. It contains about 3 percent potassium and a wealth of trace minerals, including iron, magnesium, calcium, phosphoric acid, and many others.
What to Consider When Choosing the Best Organic Fertilizer
All organic fertilizers are not created equal. Before buying and applying, learn which products act fast, which offer season-long feeding, and which will offer benefits other than nutrient delivery. Some fertilizers can even influence soil structure. Different crops have different requirements, so be sure to buy and apply what your plants need.
Dry vs. Liquid
Dry organic fertilizers should be worked into the soil for best results. Unlike synthetics that dissolve with irrigation or rainwater, organic fertilizers must be broken down by beneficial soil microbes before they can be absorbed by plants. Use these granular fertilizers at planting time to provide a long, slow feed for the duration of the growing season.
Liquid organic fertilizers offer a quick-feed option, typically packaged in a concentrated form that must be diluted with water. Mix at just the right strength for the plants you are tending. Young seedlings awaiting planting day may only need a half-strength feeding. Leafy greens benefit from a full-strength application as they approach maturity. Use liquid fertilizer to provide a strategic nutrient boost at just the right time of the season.
Fertilizers primarily include the macronutrients nitrogen (N), phosphorus (P), and potassium (K). Plants use these three elements in the greatest quantities. They are typically indicated on the front of the package in a numerical display, representing the percentages by weight of N-P-K. Fertilizers also contain micronutrients and other beneficial components.
- Nitrogen is present in chlorophyll, which produces the green color in plants and helps create their food source. This element stimulates lush, leafy growth.
- Phosphorus is essential for all plant growth and involved in several functions, promoting robust root development, flowering, and fruiting.
- Potassium regulates metabolic processes in the plant, establishing strong stems and further encouraging growth. This element boosts cellular defences against pests and diseases.
- Micronutrients including boron (B), zinc (Zn), manganese (Mn), iron (Fe), copper (Cu), molybdenum (Mo), and chlorine (Cl) in lesser quantities support overall plant health. Look for micronutrient contents on the back label of the fertilizer package.
- Microbes include soil-dwelling organisms that occur naturally in healthy soils, though populations may be lacking or spotty in a garden plot. Organic fertilizers often include dormant bacteria and fungi cultures to unlock nutrients and improve the efficacy of the fertilizer.
Note that side effects of using organic fertilizer include superficial fungal growth on the soil surface and attraction to worms and insects, neither of which are bad for plants.
Fertilizers are available in a variety of nutrient ratios, such as 10-10-10, 5-10-5, 0-5-0, and 1-0-0, partly because different plants use nutrients in different quantities. Keep the following standards in mind when selecting an appropriate fertilizer for your garden:
- Leafy plants like lawn grasses and salad greens are often considered “hungry” because of the amount of nitrogen they consume.
- Fruiting plants like tomatoes, cucumbers, and sweet corn consume a more balanced ratio of nutrients at relatively high levels.
- Landscape perennials, trees, and shrubs have lower overall nutrient requirements but still benefit from regular applications of other elements at low to moderate levels.
When shopping for organic fertilizer, consider your ultimate goal for the application. Liquid fertilizers feed crops quickly but do not build long-term soil fertility. Granular fertilizers provide a long, slow feed but won’t give a burst of nutrients at a particular point of the growing season. In many cases, both of these products can be used to complement one another.
Soil builders are a type of organic fertilizer, worm castings and compost being the most common varieties. This fertilizer is particularly beneficial for new gardens, providing relatively low levels of nutrients yet transforming the soil structure with bulk organic matter, humic acid, and dense microbial populations. Often applied in bulk as soil amendments or mulch, gardeners typically supplement this fertilizer with other types.
Fertilizer alone does not improve the condition of poor soil. If the ground is especially bad for growth, such as hardpan, sand, or gravel, add liberal amounts of organic matter in the form of compost, leaf mold, aged manure, and aged hardwood chips. The best garden strategy is to build a good soil structure with soil builders first, then follow up with other fertilizers.
To establish a fertilization program, start with a soil test. The results will show the current pH, nutrient levels, and organic content, and indicate necessary treatments to turn the plot into a productive garden. Annual soil testing can provide a system of nutrient benchmarking that will help you create an effective fertilization plan.
Our Top Picks
Several well-known brands offer excellent organic fertilizers, so it can be tough to choose. These recommendations consider the products’ nitrogen-phosphorus-potassium (NPK) analysis, ingredients, application method, and effectiveness in each category. Read on to discover some of the best organic fertilizer for thriving gardens.
From Jobe’s Organics, this all-purpose granular fertilizer is a fast-acting and balanced (4-4-4 NPK) organic fertilizer made from feather meal, bone meal, processed poultry manure, and sulfate of potash. It also includes multiple strains of beneficial archaea, bacteria, and fungi that quickly facilitate the transfer of nutrients to plants. Over time, these microbes work with the plant to improve the surrounding soil structure.
This is an optimal regular maintenance fertilizer for annuals, perennials, edibles, trees, shrubs, and almost all outdoor gardens. Be aware that excessive odor can be detected with this product. Minimize the odor by mixing this fertilizer with soil, rather than applying it on the surface.
Neptune’s Harvest has created a 2-3-1 NPK organic fertilizer made from North Atlantic fish and seaweed. This convenient liquid concentrate can nourish most types of plants, indoors and out. Simply mix the concentrate with water according to the label directions and apply it to the root zone.
The high phosphorus ratio stimulates deep root growth while boosting flower and fruit quality. This is a concentrated fish-based fertilizer, so the undiluted concentrate has an odor; however, the smell fades quickly, even when used on indoor plants.
A little goes a long way—houseplants use 1 tablespoon per gallon of water. Outdoor plants use 1/8 cup per gallon of water. Handle the product with gloves while diluting the concentrate.
These Jobe’s Organics fertilizer spikes deliver 4-4-4 NPK plant food directly to the plant’s root zone. They eliminate the mess of handling fertilizer with no required measuring or mixing. Use the 50 included spikes for indoor or outdoor containers or in planting beds.
In spring or early summer, simply insert the required number of spikes (based on container size or square feet of bed space) around each plant. Beneficial microbes in the formula help to break down the fertilizer for plants, increase soil organic content, and boost plant disease-resistance throughout the growing season.
Be sure to fully insert the spikes into the soil and cover them after installation. The beneficial microbes include several species of mycorrhizal fungi that can appear as fuzzy white growth if not completely buried.
Wiggle Worm’s organic fertilizer is an ideal soil builder as it is made of 100 percent screened worm castings, with no wood chips or other filler. Earthworms are high-level soil builders that consume large quantities of rich organic material. The raw materials in this fertilizer contain a variety of minerals and trace elements. The worms digest the materials to chemically and physically convert them into a fertile soil amendment. The end product improves the soil’s water-holding capacity and aeration. It also includes a diversity of beneficial microbes that contribute to root development and boost overall plant health and vigor.
The worm castings in this fertilizer add an odorless, nutrient-rich component to supplement any organic gardening system. It is ideal for indoors or out, including houseplants, flowers, edibles, and more. It’s an efficient way to boost the soil’s biodiversity. At the recommended application rate of just ½ cup per plant or 1 cup per foot of row, a little goes a long way. Apply on the soil surface at two-month intervals during the growing season, or mix with potting soil during repotting.
The Advantages of Using Organic Fertilizer
Organic fertilizer supplies the nutrients that plants need in a naturally slow-release form, at a rate at which plants can use them. The plant food is made available through the biological action of beneficial microbes that work together with plants. Microbes consume the organic fertilizer ingredients and release the nutrients in a form from which the plants can benefit.
Plants shed leaves and roots that become soil organic matter that microbes can colonize. A healthy soil ecosystem includes a diverse array of life that helps manage this organic matter. Earthworms and beetles consume and break down dead plant material at the soil surface and carry it to the plant root where the microbes complete the cycle.
A residual effect of the beneficial microbes is their ability to reproduce and work within the natural nutrient cycling system. When managed well, an organic system increases the carbon content of the soil over time. The increased soil carbon, in the form of humus, enhances fertilizer efficiency by absorbing water and nutrients that would otherwise runoff.
- Organic fertilizer feeds plants at a naturally slow, steady rate.
- Organic fertilizer supports healthy, diverse soil ecology.
- Organic fertilizer increases fertilizer efficiency.
Tips for Using Organic Fertilizer
The key to effectively using organic fertilizer lies in understanding how it works. It takes time and warm temperatures for soil microbes to consume the product and then release plant-ready nutrients. In cool weather, it may take up to 6 weeks to see results, but 2 weeks is typical during the growing season.
Once applied, these naturally slow-acting products continue to feed through the whole gardening season. Get an early start by fertilizing at the time of planting seeds or 2 weeks before planting seedlings. The microbes that make these fertilizers available live within the soil.
Incorporate the fertilizer into the top 3 to 6 inches of the soil where they can access it. Use liquid organic fertilizer to supplement granular fertilizer when crops need a boost of nutrients, as when cabbage plants begin to form heads or when tomatoes begin to set fruit.
- Incorporate organic fertilizer into the soil for best results.
- Apply granular organic fertilizer once at the beginning of the season.
- Use liquid organic fertilizer when plants need more nutrition.
FAQs About Organic Fertilizers
If you’re just starting out with organic fertilizer, you may have a few concerns. Below, we’ve answered some of the most frequently asked questions about buying and using these products.
Q. What are the types of organic fertilizer?
Organic fertilizer ingredients vary widely but can be categorized as plant-based, animal-based, and mineral. Most organic fertilizers contain a combination of these types to provide a balance of essential macro and micronutrients, plus beneficial microbes that help make the nutrients available. Dry or granular fertilizers feed all season, while liquids provide a quick burst of nutrients.
Q. How can you tell if fertilizer is organic?
The easiest way to tell if fertilizer is organic is to check the label. Organic fertilizer companies work hard to be certified organic and typically include the word “organic” in the product name. Also, on the back of the package, you’ll find the ingredients list.
Organic ingredients are the by-products of plant and animal processing, including alfalfa meal, soybean meal, cottonseed meal, blood meal, bone meal, feather meal, composted manure, and others. Organic fertilizer does not include ammonium nitrate, superphosphate, potassium sulfate, or other synthetic ingredients.
Q. What type of nutrient is the most important for the plants?
The most volatile and most commonly lacking nutrient in soil is nitrogen, as it quickly turns into a gas and is released into the atmosphere. Other nutrients may persist in the soil for longer periods of time. However, nitrogen, phosphorus, and potassium are all needed in such quantities that they are considered macronutrients that must be replenished for healthy plant growth.
Q. How do you apply organic fertilizer to plants?
Apply organic fertilizer to the soil around the plants. Beneficial microbes within the soil release the nutrients from the fertilizer, making them available for plants to use.
Q. Can you over-fertilize your plants with organic fertilizers?
Yes. Although many organic fertilizers are promoted as non-burning, other problems can arise from excess nutrient loads, including insect and disease infestations. Ideally, follow fertilizer recommendations based on soil sample results. In the absence of a soil sample, follow the directions on the fertilizer label.