Soil & Amendments

A complete soil reference — amendments and what they do, proven mix recipes for every context, how to identify and fix nutrient deficiencies, and why pH controls everything.

Soil amendments change the physical structure, chemistry, or biology of your soil. Knowing what each one does — and when to use it — prevents expensive mistakes.

Organic Matter & Compost

Compost (homemade or municipal)

Adds organic matter, feeds soil biology, improves drainage in clay, improves water retention in sand. The most universally beneficial amendment.

Rate: 2–4 inches worked in annually, or as needed
When: Spring before planting, fall after harvest

Aged Manure

High nitrogen, improves structure, feeds microbial life. Must be fully composted before use — fresh manure burns plants and carries pathogens.

Rate: 1–3 inches worked in
When: Fall application preferred — composting continues over winter

Coop Litter (composted chicken litter)

Superior to bagged manure — higher nutrient density (especially nitrogen and phosphorus), richer microbial population, more diverse biology. Use over purchased manure whenever you have access to it. Also superior to mushroom compost for nitrogen content.

Rate: 1–2 inches worked in
When: Compost for 90+ days before use. Do not apply fresh to edible crops.

Mushroom Compost

Byproduct of mushroom farming — spent mycelium substrate. Excellent if coop litter is unavailable. High in calcium, improves water retention, adds fungal networks to soil. Slightly alkaline — not ideal for acid-loving plants.

Rate: 2–3 inches worked in
When: Spring or fall

Worm Castings

The highest-quality, most biologically active compost available. Exceptional for containers and seedling mixes. Expensive at scale but worth it for high-value applications.

Rate: 10–25% by volume in mixes, or 1 inch as top dressing
When: At planting or as tea drench anytime

Peat Moss

Excellent water retention, slightly acidic. Sustainable concerns — slow to regenerate. Coir is a more sustainable alternative for most uses.

Rate: 25–30% by volume in mixes
When: Mix into potting media or raised bed mix

Coir (Coconut Fiber)

Sustainable alternative to peat. Similar water retention, neutral pH, excellent aeration. Better drainage than peat.

Rate: 20–30% by volume in mixes
When: Mix into potting or raised bed mixes

Drainage & Aeration

Perlite

Volcanic glass expanded by heat. Improves drainage and aeration, never breaks down, pH neutral. Non-negotiable in container mixes. Prevents compaction over time in raised beds.

Rate: 10–20% by volume in raised beds; 20–30% in containers
When: Mix into media at setup — add more to existing beds as top dressing worked in

Vermiculite

Mica mineral expanded by heat. Better water and nutrient retention than perlite but less drainage. Better for seedling mixes. Perlite is preferred for mature garden beds.

Rate: 10–20% by volume in seedling or seed-starting mixes
When: Seedling mixes, not primary garden mixes

Coarse Sand

Improves drainage in clay soils. Must be coarse/horticultural sand — fine sand (play sand or beach sand) compacts with clay and creates concrete-like conditions.

Rate: 25–30% for clay amendment, 10–15% in general mixes
When: Mix into heavy clay soils to improve drainage

Biochar

Charcoal created by pyrolysis of organic material. Improves water retention, increases cation exchange capacity (CEC), provides long-term carbon storage. Charge with compost or fertilizer before use — raw biochar absorbs nutrients from soil temporarily.

Rate: 5–10% by volume
When: Mix in at planting. Effects build over multiple seasons.

Nutrients & Fertilizers

Blood Meal

Very high nitrogen (12–13%). Fast release. Use sparingly — easy to over-apply. Deters deer.

Rate: 1–2 lbs per 100 sq ft
When: Early spring when nitrogen is needed fast. Not for fall application.

Bone Meal

High phosphorus (15–27%) and calcium. Promotes root development, flowering, and fruiting. Slow release.

Rate: 2–4 lbs per 100 sq ft
When: At planting for root crops, bulbs, and fruiting plants

Kelp Meal

Full spectrum of trace minerals, natural growth hormones (cytokinins), improves stress resistance. Low NPK but excellent as a supplement for micronutrients.

Rate: 1–2 lbs per 100 sq ft
When: Spring at planting or as foliar spray (kelp extract)

Greensand

Mined marine sediment. Very slow-release potassium and trace minerals. Excellent long-term soil builder — can take a full season to show effects.

Rate: 5–10 lbs per 100 sq ft
When: Fall application preferred for spring benefit

Fish Emulsion

Fast-acting liquid nitrogen with trace minerals. Excellent as a quick feed mid-season. Distinctive smell — normal and temporary.

Rate: Dilute 2–3 tbsp per gallon water, apply as drench
When: Mid-season boost for heavy feeders (corn, tomatoes, leafy greens)

pH Adjustment

Agricultural Lime (Calcitic)

Raises pH in acidic soils. Also adds calcium. Slow-acting — apply months ahead of planting season for best results.

Rate: 5–10 lbs per 100 sq ft to raise pH by ~1 point (varies by soil type)
When: Fall application for spring gardens

Dolomitic Lime

Raises pH and adds both calcium and magnesium. Use when magnesium deficiency is also present. Do not overuse if soil already has adequate magnesium.

Rate: 5–10 lbs per 100 sq ft
When: Fall application

Wood Ash

Raises pH. Also adds potassium and calcium. Fast-acting compared to lime. Do not use near acid-loving plants. Use sparingly — easy to over-alkalinize.

Rate: 5–10 lbs per 100 sq ft — less is more
When: Spring or fall, not in contact with seeds or seedlings

Elemental Sulfur

Lowers pH in alkaline soils. Soil bacteria convert it to sulfuric acid over weeks to months — plan ahead. Best long-term solution for acidifying soil.

Rate: 1–2 lbs per 100 sq ft to lower pH by ~1 point
When: Fall application for spring effect

Pine Bark / Pine Needles

Mildly lowers pH over time. Excellent mulch for blueberries, azaleas, and acid-loving plants. More moderate and slower than elemental sulfur.

Rate: 2–4 inch mulch layer
When: Any time as mulch. Decomposes slowly — reapply as needed.

Coffee Grounds

Slightly acidic (pH 6.0–6.5, not as acidic as often claimed). Better contribution is nitrogen and organic matter than pH shift. Good addition to compost.

Rate: Mix into compost or apply as ¼ inch layer around acid-loving plants
When: Any time — do not apply thick layers, molds easily
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