Bulb onions irrigation: water stress

Drought-sensitive bulb onions need water. Find out why it matters that they get the right amount of water at the right time, and how early season stress can be particularly damaging to your bulb onion crop.

This information was last updated in 2014.

The impact of water stress and key times for irrigation

• When is lack of water most likely to damage your bulb onion crop?
• What is the impact of relying solely on rainfall?
• What are the key periods during which strategic irrigation can protect and support bulb onions?

The impact of water stress

In dry conditions, lack of irrigation significantly reduces onion canopy development and promotes early stress bulbing and premature crop ageing. The impact on yield and bulb size is significant.

Although lack of water at any stage of the growing season will affect the bulb onion crop, the lead up to bulb initiation from mid-May to early July is a critical period.

Detering growth

Water stress during this time will deter the growth of the foliage needed to for viable bulb production.

Studies suggest that early season stress can also increase production of double bulbs and pink-off types that may be rejected by packers.

An example from East Anglia (research project FV 326a) shows how important timely irrigation can be for bulb onion crops.

Typical practice

The study showed that, compared to typical irrigation practice, relying only on rainfall could reduce gross farm returns by an average of 20 tonnes of yield.

Effectively this means a net profit of little more than zero for rain-fed irrigation.

When to irrigate

Irrigation improves bulb onion crops but timing is critical.

When planning timely irrigation, the bulb onion season can be split into four main growth phases.

During each of these periods, the crop’s water needs and sensitivity are different.

• Establishment: from drilling until the appearance of 2-3 true leaves (about mid-May)
• Early season: from 2-3 true leaves to bulb initiation (around early July)
• Mid-season: from bulb initiation until egg stage (usually early August)
• Late season: from egg stage until irrigation stop

Find the irrigation summary table on the landing page for suggested irrigation regimes during these growth phases.