Blood Meal vs. Bone Meal and How to Fertilize Plants with Them

person sprinkling bone meal fertilizer before planting

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Thanks to their names, blood meal and bone meal are some of the least glamorous gardening products out there. Yet, both of these naturally derived fertilizers can provide vital nutrients to your plants. Blood meal and bone meal are commonly available in the fertilizer section of garden centers. Both are valuable soil amendments, but don't assume they can be used interchangeably. Otherwise you might end up harming your plants. When used properly, these products help plants form strong root systems and lush foliage. Here's what you need to know about when and how to use bone meal and blood meal before adding them to your garden. 

What is blood meal?

Blood meal is made from dried slaughterhouse waste, and is one of the densest non-synthetic sources of nitrogen for plants. Nitrogen is key to many aspects of healthy plant growth. For example, it’s a component of chlorophyll, which is essential for converting light into sugars that plants need for energy. Nitrogen is also a building block for new leaves and stems (that's why the youngest leaves are often the first to look yellow from a nitrogen deficiency).

Because blood meal is derived directly from a natural source rather than being manufactured, it’s considered an organic fertilizer. Some organic fertilizers are hard to quantify when it comes to nutrient make up. Blood meal is different. It has a generally consistent chemical formulation of 12-0-0. This formulation is blood meal’s Nitrogen-Phosphorus-Potassium (N-P-K) ratio. It contains 12-percent nitrogen, 0-percent phosphorus, and 0-percent potassium.  

After adding blood meal to soil, it will make nitrogen available to plants over a period of 2 to 6 weeks. Many synthetic fertilizers, and organic fertilizer such as fish emulsion, only supply nitrogen to plants for 2 weeks. Blood meal’s extended release period can be beneficial to plants when applied according to package directions. Applying too much blood meal can flood the soil with nitrogen and burn your plants. Always follow label instructions to avoid overdoing it. It's also a good idea to make a note of the date (perhaps in your garden journal) that you make an application so you don't accidentally apply another dose of blood meal too soon.

What is bone meal?

As you might guess from the name, bone meal is derived from animal bones. And although bone meal and blood meal sound similar and are both organic fertilizers, they differ in the nutrients they contribute to help plants grow. Blood meal is high in nitrogen while bone meal provides phosphorus and calcium.

Nitrogen availability in soil changes frequently, thanks to the ebb and flow of organic matter, such as decomposing leaves, mulch, and compost. The quantity of phosphorus and calcium, unlike nitrogen, is relatively stable in the soil. In fact, researchers have found that most non-agricultural soils—the soils that make up most gardens—naturally have adequate phosphorus and calcium for plant growth. 

When phosphorus levels are too high, plant roots don't develop relationships with mycorrhizal fungi, which help the roots take up water and nutrients. Special note: mycorrhizae are particularly good at gathering phosphorus from the soil. Too much soil phosphorus also can damage nearby water systems. Excess phosphorus will run off in storm water or overflow from irrigation systems. Once it makes its way into freshwater systems, it promotes algae growth and degrades the water quality overall.    

When to Use Bone Meal vs. Blood Meal

The very best way to know if your soil would benefit from blood meal, bone meal, or any additive, is to do a soil test. Available from many county extension offices, as well as a multitude of online sources, a good soil test will measure the relative acidity of the soil (pH) and the level of several essential nutrients. 

Soil tests can be done at any time of the year. For best results, test your soil before the next growing season. Fall and winter are good times to submit a soil test. There is rarely a need to test soil every year; testing soil every 3 or 4 years is usually adequate. 

A soil test report will include levels of nutrients and recommendations for soil amendments. Phosphorus and calcium, found in bone meal, are regularly included in a soil test report but nitrogen, because it changes soil quickly in the soil, is not usually reported. Instead, you’ll receive a nitrogen application recommendation based on what you intend to grow in the soil the following season.

How and When to Apply Blood Meal and Bone Meal Fertilizer

If phosphorus and calcium is recommended via the soil test, bone meal may be a good soil amendment. Blood meal is a great way to boost the nitrogen available to plants. Remember, follow fertilizer package directions exactly when applying blood meal and bone meal. This will help you avoid wasting the product, harming your plants, and potentially harming the environment.

Follow soil test recommendations carefully when adding amendments to soil. Nutrient recommendations for homeowners are often reported in the form of pounds of nutrient per 1,000 square feet. Be ready to do some math to accurately apply amendments to your garden.

For example, if a soil test report recommends adding 1 pound of nitrogen (N) per 1,000 square feet, and you want to use blood meal, the total amount you'd need to apply is based on the formulation (N-P-K ratio) and the area to be fertilized. For easy math, let’s assume the area you are fertilizing is 1,000 square feet. Remember that blood meal's N-P-K ratio generally is 12-0-0, or 12% nitrogen. That means there are 12 pounds of nitrogen in every 100 pounds of blood meal. So, you'd need about 10 pounds of blood meal to add one pound of nitrogen to your 1000-square-foot garden.

Mix bone and blood meal into the soil so plant roots can easily access it. For large, open areas like a new vegetable garden, use a broadcast spreader to uniformly distribute the product. Then use a tiller to work it into the top 3 to 4 inches of soil. Spread bone and blood meal over small areas by hand and use a garden rake or spade to mix it into the soil. Both fertilizers can also be added to planting holes of new plants if a soil test indicates a need. 

Bone meal can be applied anytime that the soil is workable. Fall and winter applications of bone meal are just as good as applying it during the growing season. Apply blood meal at planting time or when plants are actively growing—usually spring and summer. The nitrogen contained in blood meal dissipates in about 6 weeks so it's best to apply when plants can use it immediately.

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