The main difference between organic fertilizer and conventional fertilizer is the source material. Organic fertilizers are sourced from certain naturally-occurring materials whereas chemical fertilizers are manufactured from synthetic chemicals. Specific soil amendments are considered safe for organic gardening. These natural fertilizers can add nutrients and organic matter to garden soil.
What is Organic Fertilizer?
Fertilizers are materials applied to gardens to provide essential nutrients to plants. Although natural outdoor garden soil does contain essential nutrients, a good organic fertilizer will boost the nutrient availability without harming your garden. Think of organic fertilizer as a naturally-derived multivitamin for your plants!
Organic fertilizers are made from naturally-sourced materials that have been approved for use in organic gardening.Organic fertilizers such as composted leaves and herbivore manure are derived from living organisms. Some inorganic materials such as rock dust can also be considered safe for organic gardening if they are sourced from nature instead of from synthetic chemicals.
Not all naturally-sourced materials are approved for use in organic gardening due to the possibility of contamination in some materials. Synthetic chemicals are also not approved for organic use. According to the U.S. National Wildlife Federation, the average suburban lawn receives 10 times as much chemical pesticide per acre as farmland! It’s just as important to use organic lawn & garden products at home as it is to choose organic food at the market.
The Best Organic Fertilizer for a Home Garden
Choosing fertilizer can be tricky unless you know what type of soil is in your garden. A home soil test will give you a basic idea of the nutrients that your garden soil is lacking. It’s also nice to know what type of plants you’ll be growing as different plants have different nutrient needs.
Either send a sample of your garden soil to a lab for analysis or use a quick at-home test kit. In the USA, your local extension office may offer soil testing. The soil test will help you make an informed decision about the nutrients that your soil is lacking. It’s hard to shop for organic fertilizer without knowing what you’re looking for. Your garden’s soil nutrient information is very affordable data that is well worth it (especially if you end up needing less fertilizer than you thought!).
How to Make Organic Fertilizer
Learning how to make organic fertilizer is actually quite simple. You may already have some organic fertilizers in your yard! Here are some great DIY organic fertilizers you can make at home:
DIY Organic Fertilizers
- Organic Compost & Compost Tea – make nutrient-dense plant food from fall leaves
- Grass Clippings – feed your lawn with nitrogen from mulched clippings
- Worm Farm Castings – a great way to turn kitchen scraps into plant food
- Seaweed – full of micronutrients, rinse off the salt if you like
- Well-Composted Herbivore Manure – if you’re lucky enough to have it!
- Eggshells – full of calcium for your tomatoes (also makes a lovely mulch)
Once you know how to make organic fertilizer, you’ll be surprised at how much of your home and garden waste is repurposed into natural fertilizer for plants. Since an estimated 18% of municipal solid waste is composed of yard waste, diverting it away from the landfill and into plant food is a great way to cut down on household waste while also saving money.
Natural Fertilizer for Plants
The following materials make excellent natural fertilizer for plants. The estimated NPK ratio for each material is also shown (scroll down to learn about the NPK ratio):
- Earthworm Castings 1-0-0
- Rock Dust 0-0-0.2
- Liquid Seaweed 0-0-1
- Kelp Meal 1-0-2
- Fish Fertilizer 2-4-1
- Composted Cow Manure 0.5-0.5-0.5
- Composted Chicken Manure 2-2-2
These materials and other types of natural fertilizer for plants can be found at most garden centers. Natural fertilizers and soil amendments can also be ordered online (which is nice if you prefer not to carry heavy bags home from a store). Be sure to research the nutrient profiles of the natural fertilizer for plants you’re buying so you can learn how to make organic fertilizer that suits your garden soil and crops.
Buy Organic Fertilizer: Pre-Mixed All-Purpose Fertilizers
There are some great choices if you’d rather buy organic fertilizer or are looking to supplement your homemade garden fertilizers. I add a bit of store-bought organic fertilizer to my container plants, heavy-feeding garden plants, and even the lawn. Last year PRO-MIX provided me with this multi-purpose fertilizer to test and my pumpkins LOVED it! The nice thing about using an all-purpose fertilizer on the veggies was that the nearby flowers and shrubs didn’t mind it either.
All-Purpose Organic Fertilizers
- Espoma Garden Tone Organic Fertilizer 3-4-4 (USA)
- Dr. Earth Throw & Go Organic Fertilizer 5-5-5 (USA)
- Neptune Liquid Fish & Seaweed Fertilizer 2-3-1 (USA)
- Pro-Mix Granular Multi-Purpose Organic Fertilizer 7-3-3 (Canada)
- Gaia Green Organic All-Purpose Fertilizer 4-4-4 (Canada)
The all-purpose fertilizer options above can be a great way to increase the general nutrient availability in your garden soil. If you do buy fertilizer, confirm that it’s safe for organic gardening. Look for the OMRI-Listed logo or check the OMRI database (more about OMRI below).
Organic Fertilizer for Vegetables
Here are the basic types of organic fertilizer for vegetables:
- Organic Compost – Add a layer of homemade compost for overall soil health
- Compost Tea – Create a treat for the soil (and foliar spray) that’s full of beneficial organisms
- Worm Farm Castings – Compost kitchen scraps into plant food without leaving the house
- Seaweed – Rinse off the salt if you like, it’s still full of micronutrients
- Well-Composted Herbivore Manure – Do your research, all manure is not created equal
- Eggshells – Full of calcium for your tomatoes
- Pre-Mixed Organic Fertilizer for Vegetables – For an overall nutritional boost:
These kinds of organic fertilizer for vegetables are a good place to start, but there’s nothing like a proper soil test to show you exactly what nutrients your soil needs to produce delicious veggies. The data is worth it! It’s hard to know what to buy or how to make organic fertilizer for vegetables if you’re not sure what ingredients your soil is missing in the first place.
Organic Lawn Fertilizer
Organic lawn fertilizer often centres around the nitrogen that grass craves. Lawns can fertilize themselves to some extent if you set your mulching mower blade high (3″) and mulch the grass clippings into the lawn. The clippings create their own nitrogen-rich organic lawn fertilizer that meets a portion of the lawn’s nitrogen needs.
To top up the nitrogen, choose an organic fertilizer that’s formulated for a lawn (with lots of nitrogen for healthy green blades of grass and little/no phosphorus helping out flowering plants). Safer Brand’s Ringer Lawn Restore (10-0-6) remains a very popular choice.
How to Apply Organic Lawn Fertilizer
Organic lawn fertilizer is best applied in the spring and fall rather than in the heat of summer. A top dressing of an inch of compost late in the fall will also boost soil health (the earthworms will love it). I never seem to have enough homemade compost, so sometimes I use some well-composted herbivore manure to add organic matter to the lawn soil.
Back to the importance of good soil testing, turf grasses prefer a slightly acidic soil pH. The grass won’t have optimal growing conditions if your soil is quite acidic or alkaline. Adjust soil pH with lime or sulfur.
Observe the weeds in your lawn as you apply the organic lawn fertilizer. Weeds thrive in lawns that have compact, acidic/alkaline, nutrient-poor soil. They also love frequent shallow watering and low mower blades. For instance, clover indicates a lack of nitrogen and air in the soil (I actually don’t mind clover, it’s cute and it fixes nitrogen). Addressing underlying problems will do more for the health of your lawn than simply applying fertilizer now and then. Organic, nutrient-dense, aerated soil that is deeply watered on an infrequent basis and mowed no shorter than 3″ is likely to produce a lush lawn.
NPK Ratios of Organic Fertilizer
Some store-bought organic fertilizers list a ratio of three essential plant nutrients on the package. The NPK ratio lists the amounts of nitrogen, phosphorus, and potassium. The higher the numbers are, the stronger the concentration of nutrients is (but more is not always better, really high numbers are more a marketing trick than they are useful).
Organic fertilizers generally show lower numbers in their NPK ratios when compared to synthetic chemical fertilizers. This is not a bad thing at all. Synthetic chemical fertilizers can be so concentrated that they can burn plants. They can also cause excess nutrient runoff into fresh water aquifers. You’re not necessarily getting less production for your money with a natural fertilizer for plants, but you are getting a safer product because of it’s slow and steady nutrient release.
Natural fertilizers for plants are generally applied in bulk when compared to synthetic fertilizers, so they really do need to have lower NPK digits to avoid burning plants. They are also biologically active, which can lead to variation in NPK ratio between batches. Because of these considerations, some organic fertilizers may not be labeled as “fertilizer” and may not show an NPK ratio. In these cases, look for “organic soil amendments”.
“Inorganic” Materials as Organic Fertilizers
The word “organic” has a slightly different meaning in horticulture as compared to chemistry. Some fertilizers which are “inorganic” from a chemistry perspective (because they are not derived from living matter) are actually approved for organic gardening. Many mined minerals in their natural form can be considered acceptable for organic gardening. This includes rock dust, diatomaceous earth, and gypsum.
Likewise, some natural fertilizers for plants which would be considered “organic” to a chemist aren’t approved for organic gardening. This includes manure from carnivores, manure from herbivores that has not been adequately composted, and sewer sludge or biosolid products. Those garden fertilizers are generally unacceptable in home organic gardening because of the potential for pathogen and chemical contamination.
Organic Fertilizers and OMRI Listing
Always check to see if a product is safe for organic gardening before using it. In the USA and Canada, the most reliable way to check if a product is safe for organic gardening is to look it up in the OMRI database (from the Organic Materials Review Institute). Alternatively, check for the OMRI-listed logo when buying organic fertilizer at the garden center or online. For a quick organic garden fertilizer reference, check this list of acceptable and unacceptable products in an organic program from the Dirt Doctor.
Totally Not Scientific Fertilizer Rule of Thumb: Most organic fertilizers are brown and look like they’re made of composted manure. Most synthetic chemical fertilizers are brightly coloured and look like they’re made of road salt or decorative beads. If it’s made of blue crystals or green beads, it’s probably not organic.
More Organic Supplies for your Garden
Check out the Garden Supplies Page for more organic gardening product recommendations. Check out the general Organic Gardening Page for a list of organic pest control materials. Also learn how to make organic fertilizer with your fall leaves as a natural fertilizer for your plants!
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