Using 15.5-0-0 Calcium Nitrate to Prevent Blossom End Rot in Tomatoes and Peppers

Spring Fertilization Strategy for Healthier Tomato and Pepper Crops

As gardening enthusiasts and professional growers alike gear up for the spring growing season, few issues cause more frustration than discovering dark, sunken lesions at the blossom end of otherwise healthy-looking tomatoes and peppers. This common physiological disorder is known as blossom end rot (BER) and is directly linked to a calcium deficiency in the fruit — not necessarily due to a lack of calcium in the soil, but often because of inconsistent calcium uptake.

One of the most effective ways to address and prevent this issue is by using a specialized fertilizer like 15.5-0-0 calcium nitrate, which supplies both calcium and readily available nitrogen in the form of nitrate nitrogen. This blog dives deep into how 15.5-0-0 calcium nitrate works, when and how to apply it, and why it is essential for high-quality fruit production in tomatoes and peppers.

Understanding Blossom End Rot

Before diving into the solution, it’s essential to understand what causes blossom end rot:

• Calcium imbalance: Calcium is a crucial nutrient for plant cell wall formation. When it doesn’t reach developing fruit, the tissues break down, leading to characteristic black, sunken spots.
• Inconsistent watering: Calcium moves through the plant with water, so irregular watering can limit calcium flow to the fruit.
• High nitrogen levels: While nitrogen promotes leaf growth, excessive ammonium nitrogen can compete with calcium uptake.
• Soil pH and composition: Acidic or overly sandy soils may limit calcium availability or leach it away quickly.

What is 15.5-0-0 Calcium Nitrate?

Calcium nitrate (Ca(NO₃)₂) is a water-soluble fertilizer containing:

• 15.5% nitrogen, mostly in the nitrate form (NO₃-)
• 19% calcium (Ca)

This combination makes it ideal for rapid nutrient delivery and correcting calcium-related disorders. Unlike ammonium-based fertilizers, nitrate nitrogen does not compete with calcium, which means both nutrients can be absorbed effectively by the plant.

Why Tomatoes and Peppers Need Calcium Nitrate

1. Prevents Blossom End Rot

The most obvious benefit of calcium nitrate is its ability to prevent and correct calcium deficiencies that lead to blossom end rot. Applying it during key stages of fruit development ensures calcium reaches the fruit when it is needed most.

2. Provides Readily Available Nitrate Nitrogen

Nitrogen is essential for vegetative growth, but not all forms of nitrogen are equal. The nitrate form in 15.5-0-0 allows for immediate uptake by roots, promoting balanced growth without interfering with calcium transport.

3. Improves Fruit Firmness and Shelf Life

Calcium strengthens plant cell walls, which results in firmer fruits that store longer and ship better. This is crucial for both home growers and commercial producers.

4. Reduces Plant Stress

Proper calcium levels help regulate plant stress responses, including temperature fluctuations and drought conditions — both of which are common in spring and summer.

5. Supports Overall Root and Shoot Development

Beyond preventing disorders, calcium nitrate supports healthy root systems and shoot elongation, setting the foundation for strong flowering and fruiting later on.

When to Apply Calcium Nitrate

To prevent blossom end rot and optimize plant health, timing your calcium nitrate applications is key:

1. Pre-Planting (Optional)

Mix into the soil before transplanting young tomato or pepper seedlings to boost calcium levels.

2. After Transplanting (Main Application)

Apply 15.5-0-0 calcium nitrate about 2–3 weeks after transplanting, once plants are established and have begun vegetative growth.

3. Early Flowering

This is a critical stage for calcium uptake. Apply again as flower buds begin to form.

4. Early Fruit Set

Continue applications through the early fruit development stage, when calcium demand spikes.

5. Mid-Season Maintenance

Periodic feeding every 2–3 weeks throughout the growing season helps maintain consistent calcium and nitrogen levels.

How to Apply 15.5-0-0 Calcium Nitrate

1. Soil Application

• Broadcast or side-dress 1 to 2 tablespoons per plant.
• Lightly water in or incorporate into the top few inches of soil.

2. Fertigation (Drip Irrigation Systems)

• Dissolve at a rate of 1 to 2 lbs per 100 gallons of water.
• Inject into the irrigation line during regular watering intervals.

3. Foliar Application (Supplemental use only)

• Mix at a rate of 1 tablespoon per gallon of water.
• Spray on leaves once a week during early flowering and fruiting.

Note: Foliar sprays can help but are not a substitute for root uptake. Use in combination with soil feeding for best results.

Best Practices for Success

• Water consistently: Inconsistent watering is one of the primary causes of blossom end rot. Use mulch to retain soil moisture and consider drip irrigation.
• Avoid ammonium-based nitrogen fertilizers: They can interfere with calcium uptake. Stick with nitrate-based products like 15.5-0-0.
• Test your soil: Confirm that pH is in the optimal range (6.2–6.8) for tomato and pepper growth and that calcium is not being blocked due to pH imbalance.
• Don’t over-apply: Excess nitrogen can lead to excessive leafy growth at the expense of fruit production.

Additional Tips for Healthy Tomatoes and Peppers

• Mulch to retain soil moisture and suppress weeds.
• Use support structures like cages or stakes to keep fruit off the ground.
• Rotate crops each season to reduce disease risk.
• Apply balanced fertilizers (like 10-10-10) early in the season, then switch to calcium nitrate at fruiting.

Environmental Impact and Sustainability

15.5-0-0 calcium nitrate is relatively safe when applied at recommended rates, but overuse can lead to:

• Nitrate leaching into groundwater.
• Nutrient runoff that may affect local water bodies.

To mitigate risks:

• Use precision application methods (e.g., fertigation).
• Monitor soil fertility regularly.
• Store fertilizers safely away from water sources.

Final Thoughts

Blossom end rot can devastate your tomato and pepper crops — but it doesn’t have to. By incorporating 15.5-0-0 calcium nitrate into your fertilization routine, you can ensure your plants receive the calcium they need at the right time.

This simple yet powerful fertilizer not only prevents disorders but also promotes stronger fruit set, improved plant resilience, and higher yields throughout the growing season.

For premium-quality calcium nitrate and expert product recommendations tailored to your soil needs, visit Supply Solutions LLC.

Need assistance with choosing the right fertilizer for your garden?

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• Or email us at sales@mysolutionssupply.com

Let Supply Solutions LLC help you grow healthier, more productive tomato and pepper plants this season.