Why are my spring onion plants so thin and spindly?

What's likely going on

From the photos, the spring onions are tall, floppy and very slim, with some pale, dying lower leaves. A few things commonly cause this:

1. Not enough sun – Spring onions really like full sun (at least 5–6 hours of direct light). In lower light they stretch upwards to “look for” light and end up long and thin.
2. Poor or tired soil – The bed looks quite bare and a bit compact. Onions are leafy crops and need plenty of nitrogen and organic matter. In poor soil they grow slowly and stay pencil-thin.
3. Water stress – Letting the soil swing between very dry and very wet can weaken the plants. This doesn’t usually cause thinness on its own, but it adds to the problem.

There’s no clear sign of insect or disease damage in the pictures, so this looks more like growing conditions than a pest issue.

What to do

1. Check the light
   Make sure the bed gets strong, direct sun for most of the day. If a wall or building is shading them, consider moving the next planting to a sunnier spot or using containers in full sun.

2. Improve the soil
   Mix in plenty of compost or well‑rotted manure to the top 10–15 cm of soil around the plants. For a quick boost, use a balanced vegetable fertilizer or a nitrogen‑rich one (follow the packet rate).

3. Water steadily
   Keep the soil evenly moist, not soggy. Water when the top couple of centimeters feel dry. Mulch lightly with dry leaves or straw to hold moisture if your climate is very hot.

4. Trim off dead leaves
   Remove the completely yellow or dried leaves at the base so the plant puts its energy into new growth.

5. Give them time
   Spring onions don’t make big bulbs; they thicken gradually as they grow new leaves. After improving light and soil, give them 2–3 weeks and watch for sturdier, greener growth.

How to prevent it

• Always plant spring onions in a sunny place.
• Before planting, dig in compost or manure so the soil is loose and rich.
• Start with fresh seed or healthy sets rather than very old store leftovers.
• Keep a regular watering schedule, especially in hot weather.

When to worry

• If new leaves are also turning yellow from the tips down, even after feeding, check for waterlogging or root rot.
• If you see spots, slimy patches, or many insects on the leaves, identify the pest or disease before treating.
• If plants don’t respond at all after 3–4 weeks of better light, food and water, it may be easier to reprepare the bed and sow a new, better‑fed crop.