New Raised Bed Vegetable Garden: Soil Depth, Mix & Framing

Grandson wants 11.5' x 12.5' veggie garden on clay. Plans 12" of triple‑mix + compost. Asks: 1) Is 12" depth OK? 2) Other soil additions? 3) Percentages?

Depth

12" is excellent. Minimum 8" for most veg; 12‑18" ideal for root crops (carrots, beets).

Soil Mix (by volume)

• 1/3 Compost (diverse sources: yard waste, manure, food scrap)
• 1/3 Peat moss or Coconut coir (moisture retention)
• 1/3 Coarse sand / Perlite / Vermiculite (drainage) — or use native clay only if heavily amended.
• Optional: 1 cup balanced organic fertilizer per 10 sq ft.

Triple‑mix (topsoil/compost/peat) is a good base. Add extra compost + drainage material.

Frame the Bed

• Use ACQ‑treated lumber (borate, non‑toxic) or cedar/redwood.
• Avoid CCA (arsenic) or creosote.
• Framed beds hold soil, prevent erosion, last 20 years.

Reference

Square Foot Gardening by Mel Bartholomew — detailed plans, spacing, soil recipes.

Build it right once; enjoy decades of harvests.