DIY Organic Fertilizer: Demystifying Single-Ingredient Fertilizers


Single-ingredient organic fertilizers have long been a mystery to me, and since I haven’t wanted to screw things up, I’ve been using the already-blended mixes from brands like Gardner and Bloome, which have formulations that work well for the different labeled uses (acid-loving plants, flowering plants, etc). Yet using single-ingredient fertilizers, and blending them yourself, gives you a greater degree of control in tailoring your fertilizer to the plants you have and the needs of your own soil. Making your own fertilizer from bulk ingredients can also save you money over buying ready-made blends.

Why is fertilizing important? While in theory a healthy soil provides all the nutrients your plants need, in reality most gardens could use a little help. When homes are constructed, the topsoil is often scraped away and sold, and compaction from construction, the use of landscaping fabric, or having incompatible soils trucked in (sand “topsoil” set on top of an existing clay subsoil, etc) can all contribute to nutrient deficiencies for decades to come. Given the wide variety of plants we all grow and their diverse needs, I decided to tackle my fear of the single-ingredient fertilizer aisle and figure out just what all those ingredients actually are.

Bone meal contains phosphorus and calcium and is used for flowering perennials, shrubs and trees. It is also used when planting bulbs to promote the development of strong roots and early season growth, though you may want to avoid it if critters regularly dig up your bulbs, as the smell is appealing to animals.

Cottonseed meal is a strong source of nitrogen and acidifies the soil. Use cottonseed meal to feed blueberries, azaleas, rhododendrons and boxwoods. These shallow-rooted shrubs greatly benefit from the slowly released nutrients, applied in early spring to promote vegetative growth.

Crab meal is rich in chitin and helps to enhance the activity of soil microbes. Chitin is a nitrogen-containing compound that has a structure similar to cellulose. It’s found in the shells of crustaceans such as shrimp and crabs, as well as in the exoskeleton of insects. Tilled in, crushed chitin can help to combat root rot, powdery mildew, early and late blight, as well as root-knot nematodes. The nitrogen content supports foliage growth.

Feather meal is great for heavy feeders such as corn, cole crops such as broccoli, cauliflower, Brussels sprouts and cabbage, and leafy green vegetables. It’s one of the strongest, fastest-releasing sources of organic nitrogen.

Fish meal has both nitrogen and phosphorus and is great for vegetable gardens, trees and shrubs, plus flower beds. Fish meal also enhances microbial life, promotes an early season boost to your plants and helps with root development.

Greensand is made up of the blue-green mineral glauconite, which is an iron potassium silicate. Since the early 1700’s this has been a recommended soil conditioner. Greensand is used to loosen heavy clay soil and can absorb up to one-third of its weight in water. Its best use is in providing roses and tomatoes the minerals and micronutrients they need to thrive, and in the case of tomatoes, develop a rich, full flavor and nutrient profile.

Kelp meal is from the North Atlantic Ocean and is pure Ascophyllum nodosum seaweed. It’s a source of potassium (K) and is used in early spring or fall application. It also helps with improving nutrient uptake plus reduces environmental stresses. But the main benefit of using kelp and other seaweed fertilizers is that they contain growth hormones and natural plant growth regulators that help plants grow fast, healthy and strong. I personally would make sure to incorporate some kelp or seaweed into any fertilizer application.

Neem seed meal is from the Indian neem tree. The oil is extracted from the seeds and can be mixed into the soil or potting soil. While neem is often used as an insecticide and fungicide, in the fertilizer realm it is primarily of benefit because it is a vegan organic (veganic) source of nitrogen. Many of the other sources of nitrogen are byproducts of the meat industry.

Oyster shell flour contains calcium, which is great for rhododendrons and other woody plants. It’s all natural and is ground into a flour for immediate release. Oyster shell improves aeration, water penetration and texture of the soil. Excellent for balancing out acidic conditions in worm bins. The calcium also improves the uptake of nutrients, promotes strong root development and boosts the immunity of the plant.

Seabird guano increases the size of blooms as well as the number of blooms throughout the growing season for both indoor and outdoor plants. If applied mid-season, it will increase fruit development, yield, flavor and quality. Like most organic fertilizers, it also enhances microbial activity in the soil.

Soybean meal is another vegan option which has slow-release nitrogen to promote vegetative growth. Soybean meal is a cheaper alternative to feather meal.

Shrimp meal is made from ground Pacific Northwest shrimp shells. It’s an excellent all-purpose fertilizer which is rich in nitrogen, phosphorus, calcium, and chitin. This fertilize is used on garden vegetables, herbs, ornamentals, and flowers plus it’s a compost bio-activator. A bio-activator is high in nitrogen and helps to heat up your compost bin to complete the compose cycle. I know a number of people who swear by shrimp meal in growing demanding flowering perennials, so if you can get a hold of it, do try it.

Soil testing, why go organic, and veganic fertilizer options

Soil testing. Before you start tinkering with fertilizers, it’s probably a good idea to send your soil away for testing, which will give you insights as to what each area of your landscape actually needs, to make sure that you aren’t wasting money, harming your plants, or causing pollution by adding fertilizing agents that aren’t needed.

If you are going to get a soil test, make sure you confirm with them upfront that they can give you guidelines suited to a garden setting rather than an agricultural setting so they don’t give you your soil fertility recommendations based on acres, and ask whether they can provide recommendations suited for organic gardeners (I hate being told how many pounds of urea I will need to improve growing conditions, as I never know how to convert that to an organic fertilizer).

Why organic? The benefit of using organic fertilizers is that they generally release more slowly when the soil is cool and plants are slowing in their growth, and more quickly when the soil is warm and plants are really ramping things up. So they are much more responsive to what your landscape is actually doing. Another benefit is that they feed the microbes in the soil, and when you have a healthy microbial balance in the soil, the mineral matter in your soil is broken down into usable elements for your plants, which makes your landscape less reliant on you to continually fertilize and amend.

Contrast that with chemical fertilizers, which enter the soil in one great nutrient dump, only some of which is used and the rest washes away into groundwater or the sewer, leaving the plants on a constant cycle of being overfed and then underfed. Chemical fertilizers also reduce and kill microbial populations, chase away earthworms, and acidify the soil, making your landscape more dependent on regular applications. Plants that are fed that “miracle” blue stuff on a regular basis are like drug addicts, zinging around all juiced up for a bit, then wilting and unable to cope with normal stresses after the blue stuff is washed out of their root zone.

Vegetarian and vegan fertilizer. If you are vegetarian and want to avoid the use of animal byproducts in your fertilizing routine, you should be aware that plant-based organic fertilizing agents break down best when the soil is warm, since they rely on active microbial populations in order for them to be used. So you could begin the season with foliar applications of kelp and neem seed meal which is absorbed directly into leaves, then transition to cottonseed, soybean, and greensand (applied to the soil) as the season marches on.

Still overwhelmed? Check out this post, in which I share some recipes for homemade fertilizer blends that will allow you to begin dabbling in making your own and give you a base from which to experiment.

Photo credit: Flickr


9 responses to “DIY Organic Fertilizer: Demystifying Single-Ingredient Fertilizers”

  1. Great article filled with very useful information. I am glad you mentioned having a soil test done before adding fertilizer. It is so true that most folks just add whatever is the most convenient rather than what their soil actually needs.

    Great to see you posting more regularly again!


  2. Thanks, Ed! I understand people’s hesitation to get a soil test, especially with how hard it is to understand the darn things once they come back. But it’s worth the effort.

  3. […] Fertilizer: I really hope that you will avoid commercial fertilizer products whenever possible. I understand that sometimes certain plants or soils need extra care in the form of fertilizer. Please research all natural possibilities before grabbing those generic store-bought fertilizers. My absolute favorite natural fertilizer product is fish emulsion. Made from fish parts (duh), fish emulsion is high in nitrogen and other helpful nutrients for your soil. Make sure to buy a good-quality organic one (like this one). Here is a wonderful article on other types of natural fertilizers. […]

  4. I use to make my own fertilizer for over 10 years while owning a Rhododendron Ranch. Now, at 60, I am more of a chair side gardener. I often would have a hard time finding all the organic ingredients, all at once, to mix together. Putting it in 5lb cheese buckets. I found I would miss the small ingredients such as iron, microbes, minerals so I would turn to Bob n John’s additive. I do like Organic ROMEO fertilizer (Available at Singing Tree Gardens) Romeo fertilizer company is headquartered around Half Moon Bay, California. I found that I would spend the same amount of money as buying it prepared. HOWEVER, with mixing yourself you can tailor it to specific environments within your garden. I bought a soil tester and have three different soil compositions just within my fenced area (finally can have roses in what appears to be a deer sanctuary on my 10 acres) When buying plants at nurseries, I carry my ph tester and slip it in the pot to match this at home. I use chicken manure every 2 years as the salt content can build up. I NEVER use horse manure as the nematodes would devastate my plants. Now I focus on dwarf conifers and have marginal luck growing them from cuttings. Conifers live a very frugal life. I also am learning to plant the same ph and nutrient necessary plants together, very challenging for this ole master gardener to design my parterres for aesthetics.

    • Linda – wow. Thank you so much for taking the time to share such thoughtful and helpful comments. I too like John and Bob’s and use it anywhere that seems troubled. It’s had amazing benefits. Good points about personalizing your fertilizer for each area of the garden, too.

  5. Thanks a lot for sharing all of this information! I also use already- blended mixtures but it will be very nice if I can do it myself, so thanks again!

  6. I studied plants etc (Ag and Auro shop major ) all through high school 30+ years ago. We studied commercial ( chemicals) fertilizer as well as organic. It is alway best to use organic for as much as possible if not ALL soil amendments especially if for human or pet / animal consumption. Fish fertilizer ( nitrogen)is very good and will not burn roots. Molasses is a very good organic soil additive. Fish and Molasses will make great flavors in today’s flowers we can grow in back yards and cook or smoke. ALL ORGANIC makes a very safe and consumable product. ????