A Guide to Organic Fertilizers

Table of Contents

More and more, gardeners are turning away from synthetic fertilizers, worried that the chemicals they contain might leech into the water table, harm their soil and spoil their crops. Fertilizers from organic sources can alleviate some of these fears, though it is important to study up on their composition and uses before spreading them willy-nilly throughout the garden. Here’s a brief guide to a few of the most commonly available organic fertilizers.


Horse manure and green wellies
Manure is probably the best known and most widely available of the organic. It’s a combination of animal waste and bedding material and is available both in bagged form at your local garden center and from farmers and horse owners, often for free if you’re willing to do the shoveling and hauling. Most manures, regardless of the animal that produced them, are used as nitrogen-supplements.
  • Cow manure is the least nitrogen rich.
  • Chicken manure is the richest in nitrogen.
Pro tip: Most manures are hot when fresh and will burn rather than feed your plants if applied directly. Look for “composted manure” and work it into the soil one month before planting.
Another important caveat: never use the waste of meat-eating animals like dogs, cats or pigs on your garden or in your compost pile. Even the waste of indoor pets can contain dangerous pathogens that have no place in your garden.

Fish Emulsions or Fish Meal

For centuries, Native Americans have known to use the leftovers from cleaning fish as a garden fertilizer. It is particularly easy for plants to absorb and offers, along with a balanced dose of the big three–nitrogen, phosphorous, and potassium -a myriad of essential minerals and microorganisms.


Fish swimming in kelp
Available in both dried and liquid form, kelp or seaweed adds potassium to the soil, an essential plant nutrient responsible for healthy root growth and fruiting.

Blood Meal

Another organic fertilizer that increases nitrogen to feed the leafy green growth of your plants is blood meal. This is exactly what it sounds like, dried and powdered animal blood, usually cow, collected from slaughterhouse waste. Though bloodmeal is a natural product, it may not be appropriate for certified organic farming if the slaughtered cows were raised on factory farms.

Bone Meal

Cows_source of blood and bone mealBone meal is also derived from slaughterhouse byproducts, in this case, ground bones. It is naturally high in phosphorous, the nutrient plants need for fruiting and flowering.


Limestone quarryAgricultural lime is limestone rock, ground into small particles. It’s an excellent source of calcium and a great way to bring acid soils back into balance. Another form of limestone is dolomite. It provides calcium but also contains magnesium, an essential mineral for photosynthesis in plants.
Whether you choose to go with synthetic fertilizers or a more natural route, you may want to test your soil first to make sure you aren’t over- or under-feeding any essential plant nutrient. And if you do decide to go with organic sources, you have plenty of choices of products to get your soil in shape and your garden growing well.
Looking for more tips to build up healthy garden soil? Check out Compost Tips for Beginners or our Guide to Direct Composting.

Crate of organic produce


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