The belief that blood encourages plant growth extends back to ancient agricultural practices. Historically, farmers recognized the value of animal by-products, often mixing them with bone to enrich the soil and boost crop yields. This practice established the notion of blood as a potent fertilizer. The modern question is whether pouring raw blood onto a lawn will make grass grow greener.
The Nutritional Value of Blood for Plants
Blood is a rich source of nutrients required for vigorous plant growth. Its primary value is its high concentration of nitrogen, a fundamental building block for proteins and chlorophyll production. Commercial dried blood meal typically contains about 12% nitrogen by weight, making it one of the highest non-synthetic nitrogen sources available.
Blood also provides a notable amount of chelated iron. Iron is an essential micronutrient for the synthesis of chlorophyll, and the iron in blood is bound within the heme group of hemoglobin. However, the abundance of these elements does not guarantee their immediate availability for the grass to absorb.
The Required Conversion Process for Nutrient Uptake
Grass roots cannot directly absorb the complex organic compounds found in raw blood. The nitrogen and other elements are locked up in large protein molecules, making them inaccessible to the plant. A biological conversion process, driven by the soil’s microbial community, must occur first.
This process is known as mineralization, where soil bacteria and fungi break down the complex organic nitrogen into simpler inorganic forms. The proteins must be decomposed into ammonium and then converted into nitrate, which is the form of nitrogen that plant roots can readily take up. Because this microbial breakdown takes time, raw blood is not an immediate, fast-acting fertilizer.
Why Applying Blood Directly is Ineffective (and Harmful)
Applying raw, liquid blood directly to your lawn is ineffective and often causes significant harm to the grass. The primary issue is the high concentration of soluble salts and nitrogen in the raw material. This concentration creates osmotic stress, drawing water out of the grass roots and causing a “chemical burn” that leaves behind scorched, brown patches.
The application of raw blood also presents several practical drawbacks. Its high protein content attracts unwanted scavengers, such as raccoons, opossums, and dogs, which may dig up the treated area. Furthermore, the decomposition of raw blood creates a strong, unpleasant odor that can linger for days.
Commercially available blood meal, by contrast, is dried and processed, transforming the raw liquid into a stabilized, slow-release powder. This processing reduces the risk of chemical burn by metering out the nitrogen over several weeks as it is slowly mineralized by soil microbes. Unlike its raw, concentrated counterpart, the processed nature of blood meal allows it to be an effective soil amendment.