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.
Organic fertilizers come from natural ingredients like plant scraps, animal waste, and minerals. Some are liquids, and others are dry. They require minimal processing, are easy to apply, and have a consistent texture throughout the package. The best organic fertilizers can make edible or ornamental plants healthier by providing a balance of nutrients, quality ingredients, and the most appropriate application or use for the plants’ needs.
- BEST OVERALL: Jobe’s Organics 09524 Purpose Granular Fertilizer
- BEST BANG FOR THE BUCK: Espoma PT18 Plant Tone
- BEST FOR LAWNS: Milorganite 0636 Organic Nitrogen Fertilizer
- BEST LIQUID: Neptune’s Harvest Organic Hydrolized Fish & Seaweed
- BEST SLOW RELEASE: Jobe’s Organics All Purpose Fertilizer Spikes
- BEST STARTER: Espoma Bio-Tone Starter Plus Plant Food
- BEST FOR FLOWERS: Dr. Earth 707P Organic 8 Bud & Bloom Fertilizer
- BEST SOIL BUILDER: Wiggle Worm 30-lb 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. They are 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 calcium than their plant-based counterparts. These fertilizers, plus fish emulsion and shellfish fertilizer, 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 available 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. They are typically packaged in a concentrated form that must be mixed with water before application. 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, such as 10-10-10, representing the percentages by weight of N-P-K. Nitrogen stimulates lush, leafy growth. Phosphorus promotes robust root development, flowering, and fruiting. Potassium regulates metabolic processes and boosts plant defenses against pests and diseases.
There are also seven micronutrients that plants need in lesser quantities to support overall plant health, including boron (B), zinc (Zn), manganese (Mn), iron (Fe), copper (Cu), molybdenum (Mo), and chlorine (Cl). Look for micronutrient contents on the back label of the fertilizer package.
Organic systems rely on soil-dwelling organisms to unlock nutrients and make them available to plants. These microbes naturally occur in healthy soils, but their populations may be lacking or spotty in a garden plot. Organic fertilizer manufacturers often include dormant bacteria and fungi cultures within their products to inoculate the garden and improve the efficacy of the fertilizer.
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. 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 nutrients 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 another type of organic fertilizer. They are often applied in bulk, as soil amendments or mulch. Brand-new gardens especially benefit from soil builders, such as worm castings or compost. These products provide relatively low levels of plant nutrients but transform the structure of the soil with bulk organic matter, humic acid, and dense populations of beneficial microbes. Gardeners who use soil builders typically supplement plant nutrition with other organic fertilizers.
Fertilizer alone does not improve the condition of poor soil. If the ground is especially bad for growth, such as hardpan, sand, or gravel, first 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 a fertilization strategy.
To establish a fertilization program, start with a soil test. Submit a soil sample to your local Cooperative Extension Service. The results will show the current pH, nutrient levels, and organic content, and provide instructions on the 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 on the market today.
Jobe’s Organics 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, instead of applying it on the surface. Other possible 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.
Espoma Plant Tone is a slow-release 5-3-3 organic fertilizer derived from feather meal, poultry manure, cocoa meal, bone meal, cottonseed meal, greensand, humates, sulfate of potash, and sulfate of potash magnesia. Added beneficial microbes activate in the soil to increase the fertilizer’s efficiency and improve soil structure. This fertilizer is an excellent general-purpose choice for season-long use on flowers, vegetables, trees, and shrubs.
However, this organic fertilizer is not meant for houseplants, unless they will spend several weeks outdoors. It is a high-quality product but can emit a bit of a smell. Mixing it into the soil minimizes the odor. Store any unused portion in a sealed container to avoid attracting animals with the scent.
Milorganite’s Organic Nitrogen Fertilizer is a slow-release 6-4-0 NPK fertilizer composed of heat-dried microbes that have digested the organic matter in wastewater. Milorganite fertilizers have been used to maintain golf courses for nearly a century. Their slow-release formula, including 4 percent iron, stimulates strong root development and deep-green growth for up to 10 weeks. The product won’t burn grass, and it is factory tested daily for compliance with EPA standards.
Since it is a slow-release product, it requires a little patience. It takes eight to 10 weeks to see the full effect when using this fertilizer to rejuvenate a lawn. Other factors like soil pH, water, diseases, and insects also affect how green a lawn looks. If a fertilizer like this doesn’t result in a greener lawn, have the soil tested by the county’s Cooperative Extension Service. Also, bear in mind that fertilizer alone does not cause grass to grow into bare patches. It might be necessary to sow seed or lay sod in addition to fertilizing.
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. A little goes a long way—houseplants use 1 tablespoon per gallon of water. Outdoor plants use ⅛ cup per gallon of water. 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. Check the package for damage or leaks upon arrival and handle the product with gloves while diluting the concentrate.
Jobe’s Organics All Purpose 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.
Espoma Bio-Tone Starter Plus is a 4-3-3 NPK organic fertilizer derived from feather meal, poultry manure, bone meal, alfalfa meal, greensand, humates, sulfate of potash, and sulfate of potash magnesia, plus 13 species of beneficial microbes.
Bio-Tone is unique in its incorporation of humates, complex organic molecules formed within the earth during the decomposition of ancient plants and animals. They neutralize the soil and improve nutrient uptake of plants. The beneficial microbe mix in Bio-Tone includes 10 species of fungi that work in conjunction with plants to increase root mass by up to 30 percent, and healthy roots give plants the best start.
The nutrient mix includes 2.4-percent slow-release nitrogen for an extended feed time. Use this fertilizer at planting time for all outdoor plants and when repotting houseplants. Be sure to mix thoroughly with the soil to eliminate the smell. Some superficial fungal growth might appear on the soil surface after planting but is not of concern.
Dr. Earth Organic Bud & Bloom Fertilizer is a 3-9-4 NPK fertilizer made from fish bone meal, alfalfa meal, feather meal, soft rock phosphate, and mined potassium phosphate. The high phosphorus content provides ideal conditions for flowering and fruiting plants, including bulbs and rhizomes. No chicken manure or wastewater sludge means no bad smell.
This fertilizer has excellent microbe content, with more than 20 strains of beneficial bacteria and fungi to boost plant immunity and increase nutrient efficiency. Mix this fertilizer into the soil before planting for quick root establishment and heavy yields of flowers and fruit. Dr. Earth fertilizer is primarily manufactured for dry application to be incorporated into the soil ahead of planting or as a maintenance fertilizer for established plants. The label includes directions for making a fertilizer tea as well, which might be beneficial for fruit growers.
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. The microbes consume the organic fertilizer ingredients and release the nutrients in a form from which the plants can benefit. The 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 zone where the microbes complete the cycle.
A residual effect of the beneficial microbes packaged into organic fertilizer is their ability to reproduce and work within the natural nutrient cycling system that makes this material available to plants. When managed well, an organic system increases the carbon content of the soil over time. The increased soil carbon, in the form of humus, increases the efficiency of fertilizer. It absorbs water and nutrients that would otherwise runoff and makes them available to plants.
- 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 six weeks to see results, but two weeks is typical during the growing season. The benefit is that, 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 two 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. They include alfalfa meal, soybean meal, cottonseed meal, blood meal, bone meal, feather meal, composted manure, and other easily recognizable items. Organic fertilizer will not include ammonium nitrate, superphosphate, potassium sulfate, or other synthetic products.
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 nonburning, 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.