OYSTER SHELL FLOUR (36% Calcium)
Ground Calcium Carbonate Amendment for Soil Health & pH Balance
Sourced from ancient oyster shell deposits in the San Francisco Bay, this ground flour is a sustainable, natural source of calcium carbonate—perfect for buffering soil pH, improving structure, and supporting healthy plant growth.
It breaks down slowly, providing a long-lasting release of calcium and trace minerals. Oyster Shell Flour enhances nutrient availability, encourages microbial life, and helps build stronger roots and cell walls, especially beneficial for leafy greens, brassicas, fruiting crops, and compost systems.
A natural, slow-acting alternative to mined lime, ideal for growers focused on building balanced, biologically active soil.
Key Benefits
- Neutralizes acidic soils with slow-release calcium carbonate
- Strengthens plant cell walls for improved vigor and resilience
- Improves soil structure, aeration, and tilth over time
- Enhances nutrient uptake and supports microbial activity
- Great for calcium-loving crops like lettuce, spinach, broccoli, and tomatoes
- Beneficial in compost piles and worm bins—buffers acidity and supports decomposition
- Long-lasting, sustainable, and gentle on soil biology
Application Rates
Calcium carbonate neutralizes acidic soils and corrects calcium deficiencies. A soil pH test should be done to determine current acidity levels. This product is coarsely ground and becomes available gradually over more than one season. Rates are given as a range. Use the lower rate when soil pH is close to the target range or when using other liming materials. Use the higher rate on strongly acidic soils and peat-based mixes.
🌿 Garden & Landscapes: Broadcast and incorporate 1 to 7 kg per 10 m2 (2 to 14 lb per 100 sq ft) according to soil test results. Apply in early spring or late fall. Retest soil before reapplying.
🧪 Reducing Soil Acidity: Use the higher end of the range above on strongly acidic soils. Test soil pH before each application.
🪴 Top Dressing for Containers: Apply 5 to 10 ml per 4 L of container volume (1 to 2 tsp per gallon) and mix into the top 5 cm (2 in) of soil. Reapply as needed based on a soil pH test.
🌱 Soil & Potting Mixes: Incorporate 12 to 24 ml per 4 L of mix (2.5 to 5 tsp per gallon), or 5 to 10 kg per cubic metre (3.8 to 7.6 kg per cubic yard), at the time of mixing. Test pH after mixing and before planting.
Guaranteed Analysis
- Total Calcium (Ca): 36%
- Calcium Carbonate: 91%
- Calcium Carbonate Equivalent: 92%
- Passes 100-mesh TYLER Screen (<149 microns): 30% minimum
- Retained on 100-mesh TYLER Screen (>149 microns): 70% maximum
This product complies with Canada’s Organic Production Systems General Principles & Management Standards and Permitted Substances Lists (CAN/CGSB-32.310-2021 CAN/CGSB-32.311-2020)
