Soil Types & Amendments

Soil Types

Clay

Heavy soil with >40% clay. Very high nutrient and water retention but poor drainage and aeration.

clay poorly drained pH 6--8.5

Very sticky and plastic when wet, very hard when dry. Forms long ribbon. Rich but challenging. Requires significant organic matter, raised beds, or drainage tiles.

Clay Loam

Soil with 27-40% clay. Good nutrient retention but can become waterlogged. Rich and productive when managed.

clay loam moderately well drained pH 6--8

Smooth and slightly sticky. Forms a firm ball and ribbon. Productive with proper drainage. Benefits from raised beds.

Loam

Ideal garden soil with balanced sand, silt, and clay (roughly 40-40-20). Excellent water retention and drainage.

loam well drained pH 6--7.5

Smooth, slightly gritty feel. Forms a ball that holds shape. Considered ideal for most crops. Easy to work when moist.

Loamy Sand

Coarse soil with 70-85% sand. Slightly better water retention than sand but still very free-draining.

loamy sand somewhat excessively drained pH 5.5--7

Slightly gritty, forms a weak ball. Better nutrient retention than sand. Good for root crops.

Peat

Organic soil with >20% organic matter. Acidic, moisture-retentive, excellent for acid-loving crops.

organic varies pH 3.5--6

Dark brown to black, spongy texture. Extremely moisture retentive. Naturally acidic. Excellent for blueberries, azaleas. May need lime for most vegetables.

Sand

Coarse-textured soil with >85% sand. Very well-drained, low water and nutrient retention. Warms quickly in spring.

sand excessively drained pH 5--7

Gritty feel, loose when dry, does not form a ball when squeezed. Requires frequent irrigation and fertilization.

Sandy Clay

Soil with >35% clay and >45% sand. Heavy, dense soil with poor drainage despite sandy component.

sandy clay somewhat poorly drained pH 5.5--7.5

Gritty and very sticky when wet. Hard when dry. Difficult to work. Benefits significantly from organic matter.

Sandy Clay Loam

Soil with 20-35% clay and >45% sand. Moderate drainage with fair water retention.

sandy clay loam moderately well drained pH 5.5--7.5

Gritty but sticky when wet. Forms a firm ball. Can be difficult to work when too wet or too dry.

Sandy Loam

Moderately coarse soil with 50-70% sand. Good drainage with improved water and nutrient retention.

sandy loam well drained pH 5.5--7.5

Slightly gritty, forms a ball that breaks easily. Good for most garden crops. Easy to work.

Silt

Fine-textured soil with >80% silt. High water retention, fertile, but easily compacted.

silt moderately well drained pH 6--7.5

Very smooth, silky feel. Slippery when wet. Holds moisture well but poor structure. Add organic matter to improve.

Silt Loam

Medium-textured soil with >50% silt. Good water retention, fertile, but can crust when dry.

silt loam moderately well drained pH 6--7.5

Smooth, floury feel when dry. Slippery when wet. Highly fertile. Prone to crusting and erosion.

Silty Clay

Soil with >40% clay and >40% silt. Very heavy, slow-draining, but nutrient-rich.

silty clay poorly drained pH 6--8

Very smooth and very sticky when wet. Hard when dry. Prone to waterlogging. Needs significant amendment for most crops.

Silty Clay Loam

Fine-textured soil with 27-40% clay and >50% silt. High fertility with challenging drainage.

silty clay loam somewhat poorly drained pH 6--8

Smooth and sticky when wet. Very fertile but slow to drain. Benefits from organic matter amendments and raised beds.

Soil Amendments

10-10-10 Balanced Fertilizer

synthetic

General-purpose synthetic fertilizer with equal NPK ratios.

NPK: 10--10--10

pH effect: slightly lowers

Rate: 1-2 lbs per 100 sq ft per application

Quick-release. Apply every 4-6 weeks during growing season. Does not improve soil structure. Salt buildup risk with overuse.

Aged Manure (chicken)

organic

Composted poultry manure. High nitrogen, excellent fertilizer when properly aged.

NPK: 3--2.5--1.5

pH effect: slightly raises

Rate: 5-10 lbs per 100 sq ft, applied in fall

Very hot -- must be aged 6-12 months. High phosphorus may accumulate. Use sparingly.

Aged Manure (cow)

organic

Composted cattle manure. Good general fertilizer and soil conditioner.

NPK: 0.6--0.4--0.5

pH effect: slightly raises

Rate: 20-30 lbs per 100 sq ft, applied in fall

Must be aged 6+ months to avoid burning plants and pathogen risk. Never use fresh on edible crops.

Aged Manure (horse)

organic

Composted horse manure. Good soil conditioner with moderate nutrients.

NPK: 0.7--0.3--0.6

pH effect: slightly raises

Rate: 15-25 lbs per 100 sq ft

May contain weed seeds. Ensure thorough composting. Good combined with straw bedding.

Agricultural Lime (Calcitic)

mineral

Ground limestone (calcium carbonate). Primary tool for raising soil pH in acidic soils.

pH effect: raises

Rate: 5-10 lbs per 100 sq ft based on soil test

Always soil test before liming. Effects take 2-3 months. Apply in fall. Do not apply with nitrogen fertilizers.

Alfalfa Meal

organic

Ground dried alfalfa. Balanced organic fertilizer with growth-promoting triacontanol.

NPK: 2.5--0.5--2

pH effect: neutral

Rate: 5-10 lbs per 100 sq ft

Contains triacontanol, a natural growth stimulant. Good for roses and tomatoes. Moderate release rate.

Ammonium Sulfate (21-0-0)

synthetic

High-nitrogen synthetic fertilizer that also acidifies soil.

NPK: 21--0--0

pH effect: lowers

Rate: 1-2 lbs per 100 sq ft

Fast-acting nitrogen. Acidifying effect useful for blueberries. Can burn plants if over-applied.

Azomite

mineral

Volcanic mineral dust with 70+ trace minerals. Remineralizes depleted soils.

NPK: 0--0.2--0.2

pH effect: neutral

Rate: 1-2 lbs per 100 sq ft

Contains silica, calcium, potassium, and 67 other minerals. Good for heavily cropped soils.

Bat Guano

organic

Bat droppings. High phosphorus (seabird guano is high nitrogen). Ancient organic fertilizer.

NPK: 3--10--1

pH effect: slightly raises

Rate: 2-3 lbs per 100 sq ft or 1-2 tbsp per gallon as tea

Excellent for flowering and fruiting. Can be brewed as tea for faster uptake. Sustainable sourcing is important.

Biochar

organic

Charcoal produced from biomass pyrolysis. Long-lasting soil conditioner that sequesters carbon.

pH effect: slightly raises

Rate: 5-10% by volume, charged with compost before application

Lasts hundreds of years in soil. Increases CEC (nutrient retention). Must be charged (soaked in compost tea or nutrients) before use or it will temporarily bind nutrients.

Blood Meal

organic

Dried animal blood. Very high nitrogen, fast-release organic fertilizer.

NPK: 12--1.5--0.6

pH effect: slightly lowers

Rate: 1-2 lbs per 100 sq ft, worked into soil

Can burn plants if over-applied. Good for nitrogen-hungry crops like corn and leafy greens. May attract animals.

Bone Meal

organic

Ground animal bones. Excellent slow-release phosphorus source for root and flower development.

NPK: 3--15--0

pH effect: slightly raises

Rate: 5-10 lbs per 100 sq ft, worked into planting holes

Best applied at planting time. Needs acidic to neutral pH to be available. May attract animals.

Calcium Nitrate (15.5-0-0)

synthetic

Soluble calcium and nitrogen source. Prevents blossom end rot in tomatoes.

NPK: 15.5--0--0

pH effect: neutral

Rate: 1 tbsp per gallon water as foliar spray, or 1-2 lbs per 100 sq ft

Excellent for preventing blossom end rot (calcium deficiency). Does not acidify soil unlike most nitrogen fertilizers.

Coconut Coir

organic

Shredded coconut husk fiber. Sustainable peat moss alternative for water retention.

NPK: 0--0--0.5

pH effect: neutral

Rate: Mix into soil at 10-30% by volume

Holds 8-10x its weight in water. More sustainable than peat. pH neutral. Needs supplemental nutrients.

Compost (general)

organic

Decomposed organic matter. Improves soil structure, water retention, and microbial activity.

NPK: 1.5--1--1

pH effect: neutral

Rate: 2-4 inches per year, worked into top 6 inches

Best all-around amendment. Quality varies by source. Apply annually.

Cottonseed Meal

organic

Byproduct of cotton processing. Acidifying nitrogen source.

NPK: 6--2--1

pH effect: lowers

Rate: 4-6 lbs per 100 sq ft

Good for acid-loving plants (blueberries, azaleas). Slow release over 1-4 months. May contain pesticide residues from conventional cotton.

Cover Crop Residue (Green Manure)

organic

Chopped and incorporated cover crop biomass. Adds organic matter and nutrients to soil.

NPK: 2--0.5--1.5

pH effect: neutral

Rate: Grow cover crop, then chop and incorporate 2-3 weeks before planting

Legume cover crops (clover, vetch) fix nitrogen. Grass cover crops (rye, oats) add biomass. Best practice for soil health.

Diatomaceous Earth

mineral

Fossilized diatoms (silica). Improves drainage in heavy soils. Also controls soft-bodied pests.

pH effect: neutral

Rate: 1-2 lbs per 100 sq ft for soil improvement

Use food-grade only. Also effective as pest barrier for slugs, ants, etc. Loses effectiveness when wet.

Dolomitic Lime

mineral

Limestone containing magnesium. Raises pH while supplying calcium and magnesium.

pH effect: raises

Rate: 5-10 lbs per 100 sq ft based on soil test

Use when soil test shows both low pH and low magnesium. Do not use if magnesium is adequate.

Epsom Salt (Magnesium Sulfate)

mineral

Magnesium and sulfur source. Corrects magnesium deficiency shown by yellowing leaves.

pH effect: neutral

Rate: 1 tbsp per gallon water as foliar spray, or 1-2 lbs per 100 sq ft

Only apply if soil test shows magnesium deficiency. Overuse creates nutrient imbalances. Popular but often unnecessary.

Feather Meal

organic

Ground poultry feathers. Slow-release nitrogen source lasting 3-4 months.

NPK: 12--0--0

pH effect: slightly lowers

Rate: 3-5 lbs per 100 sq ft

Very slow release; good for heavy feeders over a full season. Apply at planting.

Fish Emulsion

organic

Liquid organic fertilizer made from processed fish. Quick-release nitrogen source.

NPK: 5--2--2

pH effect: slightly lowers

Rate: 1-2 tbsp per gallon water, applied every 2-4 weeks

Strong odor. Fast-acting. Good for foliar feeding. May attract animals.

Greensand

mineral

Marine mineral (glauconite). Slow-release potassium source with trace minerals.

NPK: 0--1--5

pH effect: neutral

Rate: 5-10 lbs per 100 sq ft

Very slow release over years. Loosens clay, binds sandy soil. Iron and 30+ trace minerals. Apply at planting.

Gypsum

mineral

Calcium sulfate. Improves clay soil structure without changing pH. Supplies calcium and sulfur.

pH effect: neutral

Rate: 10-20 lbs per 100 sq ft for clay soils

Breaks up clay by replacing sodium with calcium. Does NOT change pH. Good for sodic soils.

Kelp Meal

organic

Dried, ground seaweed. Rich in micronutrients and growth hormones.

NPK: 1--0.2--2

pH effect: neutral

Rate: 1-2 lbs per 100 sq ft

Excellent micronutrient source including iron, zinc, manganese. Contains natural plant growth hormones (cytokinins).

Leaf Mold

organic

Partially decomposed leaves. Excellent soil conditioner improving structure and water retention.

NPK: 0.4--0.1--0.2

pH effect: slightly lowers

Rate: 2-4 inches as mulch or amendment

Takes 1-2 years to make. Superb water retention (holds 300-500% of its weight). Free if you have trees.

Muriate of Potash (0-0-60)

synthetic

Potassium chloride. Concentrated potassium source for fruit and root development.

NPK: 0--0--60

pH effect: neutral

Rate: 0.5-1 lb per 100 sq ft based on soil test

Very concentrated. Chloride content may harm chloride-sensitive crops (potatoes, strawberries, beans). Use sulfate of potash for these.

Mushroom Compost

organic

Spent mushroom growing medium. Rich in organic matter and calcium.

NPK: 1--0.5--0.8

pH effect: raises

Rate: 2-3 inches as soil amendment or mulch

Contains gypsum which raises pH. Not suitable for acid-loving plants. Excellent soil conditioner.

Perlite

mineral

Expanded volcanic glass. Improves aeration and drainage in heavy soils and container mixes.

pH effect: neutral

Rate: 10-30% by volume in potting mixes, 1-2 inches worked into garden soil

Lightweight, sterile, permanent. Does not decompose. Floats to surface with watering.

Pine Bark Mulch

organic

Shredded pine bark. Acidifying mulch good for acid-loving plants.

pH effect: slightly lowers

Rate: 2-3 inches as mulch

Slow to decompose. Good for perennial beds and pathways. Acidifies soil slightly over time.

Rock Phosphate

mineral

Ground phosphate rock. Very slow-release phosphorus for long-term soil building.

NPK: 0--20--0

pH effect: neutral

Rate: 5-10 lbs per 100 sq ft

Only available in acidic soil (pH <7). Lasts 3-5 years. Apply to perennial beds and orchards.

Soybean Meal

organic

Ground soybeans. Balanced slow-release organic fertilizer.

NPK: 7--1.2--1.5

pH effect: slightly lowers

Rate: 4-6 lbs per 100 sq ft

Moderately slow release. Good general-purpose organic fertilizer. Feeds soil microbes.

Straw Mulch

organic

Dried grain stalk mulch. Suppresses weeds, retains moisture, and adds organic matter as it decomposes.

NPK: 0.5--0.2--1.5

pH effect: neutral

Rate: 3-4 inches around plants, keep 2 inches from stems

May contain weed seeds. Use seed-free straw (not hay). Excellent for strawberries and potatoes. Decomposes over one season.

Sulfate of Potash (0-0-50)

synthetic

Potassium sulfate. Potassium source without chloride, safe for sensitive crops.

NPK: 0--0--50

pH effect: slightly lowers

Rate: 0.5-1 lb per 100 sq ft based on soil test

Preferred over muriate of potash for chloride-sensitive crops. Also supplies sulfur.

Sulfur (Eleite)

mineral

Elemental sulfur. Primary tool for lowering soil pH in alkaline soils.

pH effect: lowers

Rate: 1-2 lbs per 100 sq ft based on soil test

Soil bacteria convert to sulfuric acid. Takes 2-3 months. Apply in fall. Essential for blueberries in alkaline soil.

Superphosphate (0-20-0)

synthetic

Synthetic phosphorus fertilizer for root and flower development.

NPK: 0--20--0

pH effect: neutral

Rate: 2-3 lbs per 100 sq ft at planting

Fast-acting phosphorus. Apply at planting for root establishment. Environmental concern if runoff enters waterways.

Urea (46-0-0)

synthetic

Highest nitrogen content of any dry fertilizer. Quick-release synthetic.

NPK: 46--0--0

pH effect: slightly lowers

Rate: 0.5-1 lb per 100 sq ft

Very concentrated -- small amounts needed. Volatilizes rapidly on surface -- water in immediately or incorporate into soil.

Vermiculite

mineral

Expanded mica mineral. Improves water retention and aeration. Good for seed starting.

pH effect: neutral

Rate: 10-25% by volume in potting mixes

Holds water better than perlite. Good for seed starting mixes. Do not compact. Contains trace minerals.

Wood Ash

mineral

Ash from burned untreated wood. Potassium and calcium source that raises pH.

NPK: 0--1--5

pH effect: raises

Rate: 5-10 lbs per 1000 sq ft, max once per year

Fast-acting pH raiser. Do not use on acid-loving plants. Never use ash from treated/painted wood. Leaches quickly.

Worm Castings

organic

Vermicompost produced by earthworms. Gentle, balanced fertilizer rich in beneficial microbes.

NPK: 1--0.5--0.5

pH effect: neutral

Rate: 1/4 to 1/2 inch as top dressing, or 10-20% of potting mix

Cannot burn plants. Excellent for transplants and seedlings. Contains humic acid.