Library · Substrate & soil
Soil Texture Triangle.
Soil Texture Triangle
From a soil test or jar test, classify your soil and learn what it means for water, nutrients, and amendment strategy.
The mason jar test (no soil lab)
- Fill a quart mason jar 1/3 with garden soil. Remove visible rocks and debris.
- Add water to fill 2/3, plus 1 teaspoon of dishwashing detergent (helps particles separate).
- Cap and shake vigorously for 2 minutes.
- Set on a flat surface. After 1 minute, mark the level of settled material — this is the SAND layer.
- After 2 hours, mark the next level — this is SAND + SILT.
- After 24-48 hours, mark the final settled level — this is total mineral content. Anything still suspended is colloidal CLAY (or organic matter).
- Measure each layer in mm. Calculate percentages: sand = sand_mm / total_mm × 100, etc.
Texture classes & properties
| Class | Drainage | WHC* | Workability | Best for |
|---|---|---|---|---|
| Sand / Loamy Sand | Excellent (often too fast) | Low (0.05-0.10 in/in) | Easy to work | Root crops, blueberries; needs heavy organic matter |
| Sandy Loam | Good | Moderate (0.12-0.16) | Easy | Strawberries, melons, sweet potato; warms quickly |
| Loam | Excellent balance | Best (0.16-0.20) | Easy when proper moisture | Almost everything; the gold standard |
| Silt Loam | Moderate; can crust | High (0.18-0.22) | Easy when dry; sticky wet | Most vegetables; corn, soy |
| Clay Loam | Slow | High but reduced plant-available | Heavy; narrow workable window | Wheat, beans, hay; heavy feeders |
| Clay | Poor; can waterlog | Very high but ~half is unavailable to plants | Difficult; only worked at right moisture | Rice, certain pasture grasses; not ideal for vegetable garden |
* WHC = Water Holding Capacity (inches of water held per inch of soil depth, available range)
What soil texture means for management
| Issue | Sandy soils | Loams | Clay soils |
|---|---|---|---|
| Watering frequency | More frequent, lighter | Standard | Less frequent, deeper |
| Nutrient leaching | High — fertilize lightly + often | Low | Very low — tank up at start of season |
| CEC (cation exchange capacity) | Low (5-10 meq/100g) | Moderate (10-20) | High (20-50) |
| Compaction risk | Low | Moderate | High — never work when wet |
| Warm-up speed in spring | Fast | Moderate | Slow (water-heavy) |
| Best amendment | Compost (water + nutrients) | Compost (maintenance) | Compost + gypsum (structure) |
| Cover crops | Add OM | Maintenance | Break up subsoil (deep tap-root) |
Improving any soil: organic matter
Adding organic matter improves every soil — sandy, loamy, or clay — by fundamentally different mechanisms:
- Sandy soils: OM acts as a sponge, dramatically improving water holding capacity and CEC.
- Loamy soils: OM maintains structure and feeds soil biology.
- Clay soils: OM separates clay platelets, preventing them from packing tight; improves drainage and aeration.
Target: 3-5% OM for productive vegetable soil. Less than 2% indicates degraded soil; more than 8% is rare and usually peat-derived.
Free under CC BY 4.0. Cite as "OAT Soil Texture Triangle (openagriculturetechnology.com)". Classifications follow USDA NRCS standards.