How Deep to Plant Seeds: The Rule, the Exceptions, the Fixes

Plant a seed two to three times as deep as it is wide. A big bean goes 3-5 cm down; a tomato seed about half a centimeter; fine basil barely under the surface. The logic is energy: a seed carries fuel proportional to its size, and that fuel must last until the shoot reaches light.

When in doubt, shallower. A slightly exposed seed can still root; a deeply buried one is simply gone.

This is why "how deep" has no single answer and why per-species instructions beat rules of thumb: the rule gets you close, the species data gets you right.

• Surface sowers: lettuce, many petunias, snapdragons, and most fine herb and flower seeds germinate in response to light; press them onto the soil, do not bury
• Darkness lovers: a smaller group (calendula, some delphiniums) germinates better covered
• Depth as protection: corn and beans in cool spring soil are sometimes planted at the deeper end to reach stable moisture

Depth's neighbor mistake is crowding. Seeds are cheap and thinning feels wasteful, so beginners skip it, and get a row of competing, stunted seedlings. Sow at the packet spacing or slightly denser, then thin ruthlessly to the strongest. The thinnings of many greens are edible, which softens the guilt.

Nothing came up: dig gently along the row. Swollen, rotting seeds mean too deep, too wet, or too cold. No seeds found means birds or rodents shopped before you harvested. Sprouts that died just below the surface mean crusted soil or depth just beyond the fuel tank. Each failure has a different fix, and thirty seconds of forensic digging tells you which one you owe the next sowing.