Blood meal is an organic fertilizer derived from dried animal blood. Gardeners prize this product for its extremely high nitrogen content, often translating to an NPK ratio around 12-0-0. This means it contains about 12% nitrogen with minimal phosphorus and potassium. As a soil amendment, blood meal is used to correct nitrogen deficiencies and provide a powerful boost for plants. For tomato plants, which are heavy feeders, blood meal can be a beneficial nutrient source when applied strategically and in moderation.
The Role of Nitrogen in Tomato Growth
Nitrogen is a primary macronutrient responsible for driving vegetative growth in tomato plants, promoting strong stems and lush, green foliage. It is a foundational component of chlorophyll, the pigment that allows plants to perform photosynthesis and convert sunlight into the energy needed for growth. Supplying adequate nitrogen in the early stages helps establish a robust structure capable of supporting the later demands of flowering and fruiting.
The tomato life cycle begins with a vegetative phase (0 to 7 weeks), when the plant’s demand for nitrogen is highest. During this period, the plant focuses on producing biomass, and a nitrogen-rich fertilizer ensures rapid tissue development. Once the plant transitions into the flowering and fruit-setting stages, its nutritional needs shift, requiring higher levels of phosphorus and potassium.
Over-application of nitrogen during the flowering stage can lead to a condition known as “all leaves, no fruit.” The plant prioritizes leaf and stem growth at the expense of flower and fruit production. This is because excessive nitrogen signals optimal conditions for continued vegetative expansion rather than reproduction. Therefore, the greatest benefit of blood meal is realized when it is used early in the season to build a healthy plant framework.
Application Guidelines for Tomato Plants
Blood meal is most effectively used in the early spring, coinciding with the transplanting of tomato seedlings into the garden. The goal is to incorporate the high-nitrogen source into the soil so the nutrients become available as the plant enters its rapid growth phase. You can mix the granular or powdered blood meal directly into the soil before planting, or apply it as a side-dressing around established young plants.
For individual plants, a general guideline is to use a small amount, such as one to two tablespoons per square foot of soil, or about one teaspoon per plant. It is crucial to lightly scratch the product into the top inch or two of soil, forming a ring around the plant base. Take care to avoid piling it directly against the stem, which prevents risking direct contact burn.
Immediately after applying the blood meal, the area must be thoroughly watered. Watering helps to dissolve the nitrogen compounds and moves the nutrients down into the root zone, activating the breakdown process. Since blood meal is a relatively fast-acting organic fertilizer, reapplication is generally only needed if the plant shows signs of nitrogen deficiency, such as yellowing leaves, and should be done conservatively every six to eight weeks.
Avoiding Over-Fertilization and Other Concerns
The primary risk associated with using blood meal is nutrient burn, or “nitrogen burn,” caused by excessive application. As a concentrated nitrogen source, too much blood meal creates a high-salt environment that damages the plant’s roots and foliage. Symptoms of this damage include yellowing or browning leaf tips and edges.
Excessive nitrogen also affects the soil environment, as the rapid release of nitrogen can slightly increase soil acidity. Gardeners should monitor soil pH, especially if applying blood meal repeatedly, as this change can be detrimental to plants that prefer neutral or alkaline conditions. If nitrogen burn is suspected, flushing the soil with large volumes of water can help dilute the concentration of salts around the roots.
A secondary concern is that the strong smell of blood meal can attract omnivorous animals like dogs, raccoons, and cats, leading them to dig up the treated area. To mitigate this, the blood meal should always be mixed into the soil and covered, rather than left on the surface. Testing your soil before application is the best way to determine if a nitrogen boost is necessary.