Why Are My Onion Sets Not Sprouting?

You planted your onion sets two or three weeks ago and the ground is still bare. Other beds are beginning to green up but your onion row shows nothing. Failure to sprout is a common early-season concern and has several distinct causes — some indicating a real problem, others simply requiring patience. Before you start digging up sets to investigate, it helps to understand what normal onion establishment looks like and what conditions it requires.

Cold soil is the most common reason

Onion sets need soil above 7°C to begin growing. In early spring — particularly if planted in March into heavy, cold, north-facing, or shaded ground — the soil temperature may not reliably exceed this. Sets planted into cold soil sit dormant rather than rooting and shooting, and can remain apparently lifeless for three to four weeks in a cold spring. This is not failure — it is the set waiting for suitable conditions. Check soil temperature at planting depth with a thermometer, or simply press your finger into the soil: if it feels distinctly cold, wait. Once temperatures rise, sets planted in cold soil will often shoot rapidly once the threshold is crossed.

Sets planted upside down

Onion sets have a distinct top (the narrow, pointed end where the dried leaf remnants are) and bottom (the flat, root-plate end). They should be planted with the pointed top facing upward. Sets planted upside down will still eventually grow — the shoot will redirect itself — but emergence is delayed by one to two weeks compared to correctly planted sets, and the plants are weaker to start. In a tray of sets, the occasional upside-down one is easily spotted: the dried tip faces downward. If you notice this before the sets are in the ground, it is worth sorting them.

Sets have rotted

If individual sets have failed to appear and neighbouring sets in the same row are growing, some may have rotted in wet, cold conditions. Push your finger down beside a non-sprouting set position: a firm set means wait, a soft collapse means it has rotted. Replant that position with a fresh set if you have spares. Rotting is most likely in very wet, cold conditions and is more common with large sets than small ones. Using firm, undamaged sets and not planting into waterlogged ground prevents most losses.

Birds have pulled them out

One of the most frustrating causes of missing onion sets is birds — particularly sparrows and starlings — which are attracted by the dangling dry leaves at the tip of the set and pull them clean out of the ground out of apparent curiosity rather than hunger. Check around the bed for sets lying on the surface. Covering the bed with fleece or a low mesh barrier for the first two to three weeks after planting, until the sets have rooted firmly, solves this completely. Once sets are well-rooted they are rarely disturbed by birds.