Guaranteed Analysis
Nutrient Breakdown
N · Nitrogen0%
N/A — Rock phosphate contains no nitrogen, making it ideal for targeted phosphorus supplementation without stimulating excess leafy growth.
P · Phosphorus12%
Delivers slow-release phosphorus that promotes vigorous root development, abundant flowering, and strong fruit and seed production.
K · Potassium0%
N/A — Rock phosphate contains no potassium. Pair with a potash source like 0-0-60 or Greensand for complete P-K supplementation.
Derived from: Finely ground natural rock phosphate (calcium phosphate mineral deposits)
Overview
What It Is
Rock phosphate is a naturally occurring mineral mined from ancient marine deposits rich in calcium phosphate. It has been used as a soil amendment for over a century and remains one of the most trusted phosphorus sources in organic and sustainable agriculture. The mineral is crushed and finely ground to increase surface area, which helps soil biology break it down into plant-available forms more efficiently.
Unlike water-soluble phosphorus fertilizers, rock phosphate does not dissolve on contact with moisture. Instead, it relies on soil acidity and microbial activity to slowly convert its phosphorus into forms plant roots can absorb. This means it works best in soils with a pH below 7.0 and in biologically active soils rich in organic matter.
Gardeners and farmers choose rock phosphate when they want to build long-term phosphorus reserves without repeated applications. A single heavy application can feed the soil for 3-5 years, making it both cost-effective and low-maintenance.
Crop Fit
Best For
TomatoesPeppersFruit TreesRoot VegetablesBulbsFlowering PerennialsStrawberriesGarlic
Rock phosphate excels with heavy-feeding fruiting crops like tomatoes and peppers that demand strong root systems and continuous bloom production. Fruit trees benefit enormously when rock phosphate is worked into the planting hole. Root vegetables such as carrots, beets, and potatoes rely on phosphorus for tuber and root expansion. Bulbs — including garlic, onions, and ornamental bulbs — use phosphorus to build energy reserves for overwintering and vigorous spring emergence.
Application Rates
How Much to Use
| Garden & beds | 5-10 lbs per 100 sq ft |
|---|
| Lawn | 25-50 lbs per 1,000 sq ft (for severe deficiency only) |
|---|
| Trees & shrubs | 1-5 lbs per tree; 1 lb per inch of trunk diameter |
|---|
| Containers | 1-2 tbsp per gallon of soil, mixed into potting media |
|---|
| Frequency | Every 3-5 years based on soil test results |
|---|
Step by Step
How to Apply
1Soil Test
Test your soil pH and phosphorus levels first. Rock phosphate works best in acidic soils (pH below 7.0).
2Calculate Rate
Calculate how much rock phosphate you need based on soil test phosphorus recommendations.
3Broadcast
Broadcast evenly over the garden bed or around the drip line of trees and shrubs.
4Incorporate
Work into the top 4–6 inches of soil with a rake or tiller for root-zone placement.
5Water In
Water the area thoroughly after application to begin slow mineral phosphorus release.
6Longevity
Reapply every 3–5 years based on follow-up soil tests. Rock phosphate releases very slowly over multiple seasons.
Start with a soil test to confirm your phosphorus levels are actually low — excess phosphorus can lock out other nutrients like zinc and iron. If your soil pH is above 7.0, consider using a more soluble phosphorus source or amending with sulfur to lower pH first. For garden beds, broadcast the recommended rate evenly across the surface, then incorporate it into the top 4-6 inches of soil. For trees and shrubs, dig a trench around the drip line 4-6 inches deep, spread the rock phosphate evenly, and backfill. Water thoroughly after application.
Handling & Timing
Safety & Season
Safety & Storage
Rock phosphate is a low-toxicity natural mineral, but the fine powder can irritate eyes, skin, and lungs during application. Wear a dust mask, gloves, and eye protection when spreading. Store in a cool, dry location in the original sealed bag.
Seasonal Notes
Spring is the ideal time to apply rock phosphate, as rising soil temperatures and moisture activate microbial breakdown. Work it into beds 2-4 weeks before planting. Fall application also works well, especially when preparing new garden beds or planting garlic and bulbs. Summer topdressing is less effective since rock phosphate needs incorporation.
In Context
How It Compares
Rock phosphate vs. Triple Superphosphate (TSP): TSP delivers phosphorus immediately in water-soluble form but can leach and contribute to runoff. Rock phosphate releases slowly over years with minimal environmental risk. Rock phosphate vs. Bone Meal: Both are organic phosphorus sources, but bone meal breaks down faster within one growing season. Rock phosphate lasts 3-5 years and is vegan-friendly.
Answers
Frequently Asked Questions
What is rock phosphate fertilizer?
Rock phosphate is a natural, mined mineral fertilizer with an NPK ratio of 0-12-0, providing 12% phosphorus (P₂O₅) with no nitrogen or potassium. It is one of the oldest and most natural phosphorus sources available, formed from ancient marine deposits over millions of years. Rock phosphate releases phosphorus very slowly as soil acids and microbial activity gradually break down the mineral particles — providing sustained phosphorus availability over months to years rather than weeks. Old Cobblers Farm™ Wicked Organics 0-12-0 Rock Phosphate is an OMRI-Listed organic phosphorus amendment for long-term soil building.
What is rock phosphate used for in the garden?
Rock phosphate is used to build long-term phosphorus reserves in garden soil. Unlike fast-acting synthetic phosphorus, rock phosphate breaks down gradually, providing a sustained phosphorus supply that supports root development, flowering, and fruiting over multiple growing seasons. It is especially popular in organic gardens, permaculture systems, and long-term soil improvement programs where building lasting soil fertility is the goal. Rock phosphate also supplies calcium and trace minerals. Old Cobblers Farm™ Wicked Organics 0-12-0 Rock Phosphate is ideal for gardeners investing in long-term soil health rather than quick-fix nutrition.
How do I apply rock phosphate?
Apply rock phosphate by broadcasting 5–10 pounds per 100 square feet and incorporating deeply into the top 6–8 inches of soil. Because rock phosphate does not move through soil and releases nutrients slowly, thorough incorporation into the root zone is essential. For new garden beds, mix into the soil during initial preparation. For established beds, work into the soil surface as deeply as practical. Apply in fall or early spring to allow maximum time for breakdown before peak growing season. Old Cobblers Farm™ Wicked Organics 0-12-0 Rock Phosphate is most effective when deeply incorporated into the planting zone.
What is the difference between rock phosphate and triple superphosphate?
Rock phosphate (0-12-0) is a natural, slow-release phosphorus source that breaks down over months to years, ideal for organic programs and long-term soil building. Triple superphosphate (0-46-0) is a concentrated, water-soluble form providing nearly four times the phosphorus that becomes available quickly. Rock phosphate works best in acidic soils (pH below 6.5) where it dissolves more readily, while TSP is effective across all pH levels. Choose rock phosphate for slow, sustained feeding and TSP for immediate phosphorus needs. Old Cobblers Farm™ offers both Wicked Organics Rock Phosphate and Wicked Growth 0-46-0 TSP.
Does rock phosphate work in alkaline soil?
Rock phosphate is less effective in alkaline soils (pH above 7.0) because the mineral requires soil acids to break down and release plant-available phosphorus. In neutral to alkaline soils, rock phosphate may take significantly longer to become available or may remain largely unavailable to plants. For alkaline soils, triple superphosphate (0-46-0) or bone char are better phosphorus choices because they are already in plant-available forms. A soil test indicating both pH and phosphorus levels helps determine the best option. Old Cobblers Farm™ Wicked Organics Rock Phosphate performs best in soils with pH below 6.5.
How does rock phosphate compare to bone meal?
Rock phosphate (0-12-0) and bone meal (3-15-0) both provide phosphorus but differ in origin, release speed, and additional nutrients. Bone meal is an animal byproduct that releases phosphorus more quickly and also provides nitrogen and calcium. Rock phosphate is a mined mineral that releases phosphorus much more slowly but persists in soil for longer. Bone meal may attract digging animals, while rock phosphate does not. Both are OMRI-Listed for organic use. Old Cobblers Farm™ offers Wicked Organics Rock Phosphate for long-term soil building and Bone Meal for faster phosphorus availability.
What is the NPK of rock phosphate?
Rock phosphate has an NPK ratio of 0-12-0, meaning it provides 12% phosphorus (P₂O₅) with no nitrogen or potassium. While 12% is lower than concentrated synthetic phosphorus sources like triple superphosphate (46%), rock phosphate compensates with its extremely long residual effect in soil — a single heavy application can supply phosphorus for 3–5 years. It also provides 20–30% calcium and various trace minerals not found in synthetic alternatives. Old Cobblers Farm™ Wicked Organics 0-12-0 Rock Phosphate delivers lasting organic phosphorus from a single natural mineral source.
