AZ soil prep & amendment — fix what the desert left out.

What AZ soil is actually missing

• Organic matter — typically less than 1%, vs. 5%+ in productive growing regions.
• Available iron — soil pH above 7.5 locks up iron, even when the test shows plenty.
• Nitrogen — virtually none in undeveloped desert soil.
• Available phosphorus — bound up by high pH and calcium.
• Soil biology — fungal networks, beneficial bacteria, earthworms.

The 4 amendments that move the needle

• COMPOST — 2–3 inches worked into the top 8" of soil. The single highest-impact amendment.
• ELEMENTAL SULFUR — 1 lb per 100 sq ft to slowly lower pH. Works over months, not weeks.
• CHELATED IRON (EDDHA form) — the only chelate that stays available in AZ alkaline soil.
• MULCH — 3" deep on the surface, every bed, year-round. Feeds biology, moderates temperature, retains water.

Test before you spend

An AZ soil test costs $35 and tells you exactly what to add. Skip the trial-and-error.

• U of A Cooperative Extension offers low-cost soil tests.
• Look for pH (will be 7.5–8.5), organic matter %, and available phosphorus / potassium.
• Don't trust home pH probes — they read inconsistently in AZ soil.

How to amend a brand-new bed

• Loosen native soil to 12" deep — break up any caliche layer with a digging bar.
• Spread 3" of finished compost across the surface.
• Add 1" of coarse sand if soil is heavy clay.
• Add 1 lb elemental sulfur per 100 sq ft.
• Add 2 lbs balanced organic fertilizer per 100 sq ft.
• Till or fork everything in to 8" depth.
• Water thoroughly, let it rest 2 weeks, then plant.

Maintaining the bed year over year

• Top-dress with 1" compost every spring AND every fall — the biggest single thing you can do.
• Re-mulch to 3" depth twice a year.
• Foliar feed with fish emulsion or kelp every 4 weeks during active growth.
• Rotate crop families — solanums (tomato, pepper, eggplant), brassicas, cucurbits, legumes, leafy.

What NOT to waste money on

• Gypsum — only useful for sodic soils. Get a soil test first; most AZ home soil doesn't need it.
• Generic 'soil acidifier' products — way less efficient per dollar than elemental sulfur.
• Mycorrhizal inoculants for vegetable beds — most veggies don't form strong mycorrhizal associations.
• Bagged 'cactus soil' for tomatoes (real recommendation we've seen).