Peat moss vs coco coir: which is better for your garden?

Peat moss and coco coir are often presented as interchangeable organic amendments, but they have meaningfully different properties that affect how they perform in the garden. The choice matters most for seed starting mixes and acid-loving plant.

Peat moss has been the default soil amendment for American gardeners for decades. Coco coir emerged as a sustainable alternative and is now widely available. They serve similar purposes but with meaningful differences.

What each material is

Peat moss

Peat moss is partially decomposed sphagnum moss harvested from peat bogs in Canada, Ireland, and other northern regions. Per Penn State Extension, "peat moss improves water retention in sandy soils and aeration in clay soils while providing a slightly acidic, sterile growing medium."

Formation: Peat bogs are formed over thousands of years by the accumulation of plant material in anaerobic, waterlogged conditions. Harvested at 1/16 inch per year of formation, commercial peat is effectively a non-renewable resource on human timescales. Per Oregon State Extension, "significant CO2 is released when peat bogs are drained for harvesting."

Properties:

• pH: 3.5–4.5 (very acidic)
• Sterile (no weed seeds, pathogens)
• Very low nutrient content
• Hydrophobic when dry: very difficult to rewet once completely dry
• Slow to decompose

Coco coir

Coco coir is the fibrous material processed from the husks of coconut shells — a byproduct of the coconut industry. Per University of Florida IFAS, "coco coir is a renewable, sustainable material that provides physical properties similar to peat moss."

Properties:

• pH: 5.5–6.5 (slightly acidic to near neutral)
• Rewets easily even when dry
• Slightly higher natural nutrient content (potassium, sodium) than peat
• Can be compressed into bricks for economical shipping
• Decomposes slightly faster than peat but still long-lasting