Close-up of Optimize Organics Oyster Shell Flour – natural calcium amendment for boosting soil health and balancing pH levels.
2kg bag of Oyster Shell Flour by Optimize Organics – slow-release calcium for soil pH balance and strong plant growth.
1kg bag of Optimize Organics Oyster Shell Flour – natural calcium boost for potted plants, leafy greens, and garden beds.
20kg pail of Optimize Organics Oyster Shell Flour – natural lime alternative for amending acidic soils and boosting fertility.
10kg bulk Oyster Shell Flour from Optimize Organics – ideal for vegetable gardens, compost mixes, and soil remineralization.
20kg bag of Optimize Organics Oyster Shell Flour – calcium-rich amendment for garden beds, farms, and regenerative growers.
Close-up of Optimize Organics Oyster Shell Flour – natural calcium amendment for boosting soil health and balancing pH levels.
2kg bag of Oyster Shell Flour by Optimize Organics – slow-release calcium for soil pH balance and strong plant growth.
1kg bag of Optimize Organics Oyster Shell Flour – natural calcium boost for potted plants, leafy greens, and garden beds.
20kg pail of Optimize Organics Oyster Shell Flour – natural lime alternative for amending acidic soils and boosting fertility.
10kg bulk Oyster Shell Flour from Optimize Organics – ideal for vegetable gardens, compost mixes, and soil remineralization.
20kg bag of Optimize Organics Oyster Shell Flour – calcium-rich amendment for garden beds, farms, and regenerative growers.

Oyster Shell Flour 36% Ca

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OYSTER SHELL FLOUR (36% Calcium)

Ground Calcium 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

🌿 Garden Beds:
Apply up to 1–2 kg per 10 m² (2–4 lbs per 100 ft²) once per month.

🪴 Top Dressing for Containers:
Apply 10–15 ml (2–3 tsp) per plant, or 5–10 ml per 4L (1–2 tsp per gallon) of soil. Mix into the top 5 cm (2").

🌱 Soil Mixing:
Use 30 ml per 4L (2 tbsp per gallon) of soil. For bulk mixing, apply up to 2.5 kg (5 lbs) per cubic yard.

🧪 To Reduce Soil Acidity:
Apply 1–7 kg per 10 m² based on soil test results.

Guaranteed Analysis

  • Total Calcium (Ca): 36%

  • Calcium Carbonate: 91%

  • Calcium Carbonate Equivalent: 92%


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)

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