Why Your Seeds Are Not Germinating

Work through it in this order

Seed that fails to come up is usually a condition problem rather than a seed problem. These are the causes worth checking, roughly in order of how often they are responsible.

1. Soil temperature

This is the most common cause, and it is invisible.

Iowa State Extension puts the useful range for most species at 65–75°F, and stresses that this is “the temperature of the growing medium, not the air.” Most seeds germinate somewhere between 68 and 86°F.

A propagator set in a cool room, or a seedbed sown in early spring, can be many degrees below the air temperature — especially if the soil is wet, because evaporation cools it.

Buy a soil thermometer. It removes the single largest source of unexplained failure.

2. Depth

Too deep and small seed exhausts its reserves before reaching light. Too shallow and it dries out.

The working rule is two to three times the seed’s diameter. Some species — Iowa State names celery and lettuce — need light and must be left uncovered entirely.

3. Moisture, and how consistent it is

Germination is not a single event. A seed takes up water, begins to swell and metabolise, and pushes out a root. If the medium dries during that window, the process stops and the seed usually dies.

Consistently damp is the target. Waterlogged is its own problem, because seeds need oxygen too and saturated medium has very little.

4. Crusting

A soil surface that dries into a hard crust will physically stop seedlings emerging, particularly small ones in heavy soils after heavy rain or overhead watering.

Covering fine seed with vermiculite or a light seed compost rather than garden soil avoids it.

5. Old or badly stored seed

Viability declines with age, and the rate varies enormously by species. Parsnip is notoriously short-lived and worth buying fresh each year; tomato and cucumber can stay good for years.

Heat and humidity kill seed faster than time does. A packet left in a hot shed all summer may be dead regardless of its date.

6. Pests and rot

University of Maryland Extension covers the case where seed germinates and then fails. Seed rots in cold wet soil, and damping-off fungi kill seedlings at or just below the surface — a seedling that emerges and then topples with a pinched, dark stem base is damping-off, not a germination failure.

Sowing into cold wet soil is what makes both far more likely.

The test that settles it

If you suspect the seed, run a paper towel test: damp towel, ten seeds, sealed bag, warm room. Count what sprouts after the species’ normal germination period.

Eight out of ten means your seed is fine and the problem is in your conditions. One out of ten means buy new seed.