Blood meal is a high-nitrogen organic fertilizer made from dried animal blood, commonly used by gardeners to promote leafy growth. Due to its potent composition, understanding the correct application rate is important for successful gardening. The primary challenge is balancing nutrient provision for vigorous growth with avoiding plant damage, which is a significant risk. Precise dosage is required to prevent the chemical burn that results from over-application.
What Blood Meal Provides and Why Dosage is Critical
Blood meal is valued as an organic source of nitrogen, typically displaying an NPK (Nitrogen-Phosphorus-Potassium) ratio around 12-0-0 to 14-0-0. This high concentration makes it a targeted supplement for plants exhibiting nitrogen deficiency, often characterized by yellowing or pale green leaves. Nitrogen is a component of chlorophyll, the molecule plants use for photosynthesis, and is necessary for developing healthy foliage.
The nitrogen in blood meal becomes available relatively quickly as soil microbes break down the proteins. This rapid availability, combined with its high concentration, makes precise dosage important. Applying too much blood meal saturates the soil with soluble nitrogen salts, which draw moisture out of the plant roots through osmosis. This leads to nitrogen burn and potential root and foliage damage, necessitating a cautious approach.
Calculating the Right Amount for General Soil Preparation
When preparing a new garden bed or amending soil, the goal is to mix the blood meal evenly into the growing medium. A standard application rate for general soil preparation is approximately 1 cup of blood meal per 20 to 25 square feet of garden space. This provides a baseline nitrogen boost without concentrating the salts.
For larger areas, use roughly 1 to 2 pounds per 100 square feet, with the lower end recommended for new users. The blood meal must be incorporated thoroughly into the top 4 to 6 inches of soil before planting. When preparing a potting mix for containers, a general guideline is to mix in about 1 tablespoon of blood meal per cubic foot of soil.
Application Rates for Established Plants (Side Dressing)
Side dressing involves applying the fertilizer to established, actively growing plants to provide a mid-season boost. For large, nitrogen-hungry vegetable plants like tomatoes, peppers, or corn, a typical application is 1 to 2 tablespoons of blood meal per plant. This amount should be sprinkled evenly in a ring around the base of the plant, avoiding direct contact with the stem.
For larger perennial shrubs, such as a rose bush, use 1/4 to 1/2 cup of blood meal scattered around the drip line. The drip line is the area beneath the outer circumference of the plant’s branches, where the feeder roots are located. To prevent root burn, the fertilizer must be kept at least 3 to 4 inches away from the plant’s main stem or crown.
After applying the blood meal, lightly scratch it into the top surface of the soil with a rake or hoe to help activate the nutrients. The area must be watered immediately and thoroughly; this action dissolves the nitrogen salts and carries them down into the root zone in a diluted, safer form. Reapplications should generally be limited to every six to eight weeks during the growing season, or only when signs of nitrogen deficiency reappear.
Avoiding Over-Fertilization and Plant Burn
The immediate signs of nitrogen burn from over-application are typically visible on the foliage. Leaves may develop a scorched appearance, with crispy, brown edges, or sudden yellowing and wilting. In extreme cases, the high salt concentration can blacken and damage the roots, leading to plant death.
If accidental over-application occurs, the immediate action is to flush the soil heavily with plain water. This involves slowly pouring a large volume of water over the affected area to dilute the concentrated nitrogen salts and leach them below the root zone. This heavy watering should be repeated over several days to ensure maximum dilution.
Gardeners must also avoid applying blood meal directly to wet leaves, as the moisture can cause the product to stick and create localized leaf burn. Removing existing mulch before application and replacing it afterward ensures the product is worked directly into the soil. Starting with the lowest recommended application rate provides the best defense against over-fertilization.