Blood meal is a high-nitrogen fertilizer derived from dried animal blood, typically from slaughterhouse byproducts. Gardeners primarily use this organic material to enrich soil, but it has also gained a reputation as a potential deterrent for garden pests like deer. The substance’s strong odor is thought to signal danger to grazing animals, prompting them to avoid treated areas.
The Repellent Mechanism
The theory behind blood meal’s repellent property centers on the powerful sense of smell possessed by deer. When dried blood breaks down, it releases an earthy odor that animals notice. Deer instinctively associate this scent with the presence of a predator or a recent kill, triggering a natural avoidance response.
This olfactory connection allows blood meal to function as an area repellent by creating an unpleasant environment. The lingering scent suggests the treated area is unsafe, encouraging deer to forage elsewhere.
This deterrent effect relies entirely on the concentration and persistence of the odor. If the scent fades quickly, the deer will soon perceive the area as safe and return to feeding.
Effectiveness Against Deer
The effectiveness of blood meal as a deer repellent is highly variable. Some field studies have shown that a mixture of blood meal and peppercorns, when hung in bags, can reduce browsing damage to young apple trees by over 30% compared to untreated controls.
However, blood meal is not a long-term solution and its success depends on external factors. When deer populations are high or food sources are scarce, their motivation to eat may override their natural aversion. Deer also tend to habituate to odor-based repellents over time, causing the initial effectiveness to decline. Most scientific tests suggest that even the best repellents rarely reduce deer damage by more than 50% in field trials. Blood meal offers only temporary protection and is not a reliable method for sustained deer control.
Application Techniques and Drawbacks
Blood meal can be applied in several ways to deter deer, though all methods require frequent reapplication. The simplest application involves sprinkling the dry powder around the perimeter of the garden or individual plants, typically at a rate of 3 to 13 pounds per 1,000 square feet. Care must be taken to avoid direct contact with plant leaves, as the high nitrogen content can cause burn damage.
A common alternative is to mix the powder with water to create a slurry that can be applied to the soil. Some users also advocate for placing blood meal in breathable sachets, such as cheesecloth or nylon stockings, and hanging them from stakes or branches. This hanging method helps prevent the nitrogen from over-fertilizing or burning plants while concentrating the repellent odor.
The primary drawback is the short lifespan of the deterrent effect. The blood meal’s odor diminishes quickly, especially after rain or irrigation, necessitating reapplication every three to five days for continuous protection. The scent of dried blood can also attract non-target animals, particularly dogs, raccoons, and other scavengers. If ingested in large quantities, blood meal can be toxic to dogs, potentially causing symptoms like bloody vomit and pancreatitis.