Organic Fertilizer Guide: Meals, Bone Meal, Kelp and Blended Fertilizers Explained

Fertilizer labels can look like a secret code. Once you know how to read the numbers and what each common ingredient does, picking the right product becomes much easier. This guide walks through the basics of organic fertilizers, from single-ingredient meals to ready-made blends.

What N-P-K Means

Every fertilizer label shows three numbers, such as 5-7-3. They stand for the percentage by weight of three major nutrients:

• N (nitrogen): supports leafy, vegetative growth and the green color of foliage.
• P (phosphorus): supports root development, flowering and fruiting.
• K (potassium): supports overall plant function, including water movement and fruit quality.

A bag marked 6-1-2 is higher in nitrogen, while one marked 3-15-0 is mostly phosphorus. Plants also need calcium, magnesium, sulfur and a range of trace elements, which is why many organic fertilizers and soil minerals list additional ingredients.

How Organic Fertilizers Work

Most organic fertilizers are made from plant, animal or mineral sources. Their nutrients are locked up in forms that need to be broken down by soil microbes before plants can use them. That is why organic fertilizers tend to work more slowly than soluble products, and why warm, moist, biologically active soil gets the best results. The upside is that they are usually gentler and feed the soil as well as the plant.

Browse our full range of organic fertilizer and amendments or filter down to single ingredients.

Common Single-Ingredient Fertilizers

Single-ingredient products let you target a specific need. The exact analysis varies from brand to brand, so check the label on the product you buy.

Bone meal and fish bone

Made from ground animal or fish bones, these are best known as phosphorus sources, with some calcium. Gardeners often mix them into the planting hole for bulbs, roots and flowering plants. Examples in our catalog include Down To Earth Bone Meal 3-15-0 and E.B. Stone Organics Bone Meal 1-15-0.

Kelp meal

Dried seaweed provides potassium plus a wide range of trace elements. It is low in nitrogen and phosphorus, so it is more of a supplement than a full fertilizer. Look at Down To Earth Kelp Meal as an example.

Neem seed meal, feather meal, blood meal and similar

Meals made from seeds, feathers or animal by-products are generally nitrogen sources that release as they decompose. They suit leafy crops and heavy feeders. Down To Earth Neem Seed Meal 6-1-2 is one example of a nitrogen-forward meal.

Fish and shrimp meals

Seafood-based fertilizers combine nitrogen with phosphorus and trace nutrients. See Down To Earth Shrimp Meal 6-6-0.

Manure and compost

Composted manures and compost are lower in concentrated nutrients but improve soil structure and feed soil life. Always use composted material rather than fresh manure.

Minerals

Products like gypsum, lime and rock dust supply calcium, magnesium, sulfur or trace minerals. Lime also raises soil pH, so it is best used when a soil test shows you need it. See our garden minerals.

Blended Fertilizers

Blends combine several ingredients so one product covers multiple needs. They are often labeled by crop, such as tomato and vegetable, fruit tree, citrus or acid-loving plants, and the N-P-K ratio is tuned to what that group generally prefers. They are an easy way to get a balanced, ready-to-use option without mixing ingredients yourself.

Check our blended fertilizers for ready-made mixes, such as Down To Earth Fruit Tree 6-2-4 or FoxFarm Happy Frog Citrus and Avocado Fertilizer.

Choosing Between a Blend and Single Ingredients

• Choose a blend if you want simplicity and a balanced, crop-appropriate feed.
• Choose single ingredients if you want to correct a specific shortage, tailor a mix for a particular crop, or build your own custom blend.
• Test your soil to see what is already there. Some garden soils are already high in phosphorus, and adding more will not help.

Tips for Using Organic Fertilizers

• Apply dry fertilizers by mixing them into the soil or working them lightly into the top layer, then water them in.
• Be patient. Organic fertilizers take time to act, so apply them a little ahead of when the plant will need them.
• More is not better. Over-application can burn roots or build up nutrients that wash into waterways.
• Store dry fertilizers sealed and dry, away from pets and children, and follow all label directions.

Have a fertilizer question? Shop online at dsgardensupplies.com, or pick up in store at 130 Doolittle Drive #17, San Leandro, CA 94577 (Mon-Fri, 10am-5pm Pacific). We ship nationwide via UPS. Reach us anytime at dsgardensupplies@gmail.com for help matching a fertilizer to your garden.