# Irrigating onions: when and how much water we give on a Żuławy field

Irrigation decides onion size and batch evenness. We show which growth stages we water across around 250 hectares of onions, and when we cut it off.

Onions repay water with size. We irrigate not by the calendar, but by the growth stage of the plant and by what we see in the field: how much rain has fallen, how the top layer of the mada soil looks and where the crop is in its bulbing. The most important window runs from June to the end of July, and the most important decision late in the season is not about giving water, but about cutting it off. We write this from the practice of growing around 250 hectares of onions, from which we harvest around 60 tonnes per hectare in a good season.

## How much water onions need in a season

Agronomy puts the figure at somewhere between 300 and 500 millimetres of water over a whole season, counting rainfall and irrigation together. At peak growth onions need around 3 millimetres a day, and a single pass with the irrigator usually delivers about 20 millimetres. On light soils you give less water, but more often. On heavier ones, like our mada soils, the dose can be bigger, just applied more slowly, so the water goes into the soil instead of running off the surface.

Onions are also unusually sensitive, because their root system is shallow and not well developed. They will not reach for a reserve of water in the deeper layers the way wheat or beet will. If the top layer runs short of moisture for a few days at the wrong moment, the plant simply stops building the bulb, and it never makes that up. So for us irrigation is not an emergency rescue in a drought, it is a normal part of running the crop.

## Three moments when water decides the yield

The first is emergence and the first few weeks. Even moisture gives even emergence, and even emergence gives an even batch at the end. If part of the field comes up late, those plants stay smaller right through to harvest and drop out of the main size grade.

The second is bulbing, which here means June and July. This is when size and tonnage are built, so every longer break in the water supply shows up later on the weighbridge and on the sorter. This is the window we watch most closely.

The third moment is the end of the growing season, and it works the other way round. We cut the water off so the onions can ripen quietly: the tops go over, and the skin closes and hardens. Giving water at this stage delays ripening and hurts storability, and what we want is onions that will sit in store for months. We write more about how we tell a ripe, healthy batch in our post on [how to spot good quality onions](/blog/jak-rozpoznac-cebule-dobrej-jakosci).

| Stage | What happens in the onion | Our water decision |
| --- | --- | --- |
| Emergence, first weeks | The plant puts out shallow roots | We hold even moisture, small doses |
| Intensive growth | Leaf mass builds up | We irrigate as needed, watching the rainfall |
| Bulbing | Size and tonnage are made | We watch most closely, we allow no break |
| Ripening before harvest | Tops go over, skin closes | We cut the water off and wait for ripeness |

## What we irrigate onions with here

We spread the water with a reel irrigator fitted with a boom. The boom travels over the rows and delivers water widely, in fine droplets, while the hose fed off the drum pulls it evenly across the field. The point is that the whole width of the working strip gets a similar dose, because onions react to differences: where there was less water, the size will be smaller too.

{% captionedImage src="/images/galleryPage/27.webp" alt="A boom irrigator working over rows of young onions, with the farm buildings in the background" caption="The boom spreads water in fine droplets across the full width of the working strip." /%}

Fine droplets have one more advantage on heavy soil. Water applied too violently destroys the structure of the top layer and caps the soil, and then the next rain runs off instead of soaking in. Our field equipment, from the onion harvester to the satellite guidance, is shown in the [machinery park](/park-maszynowy).

## In Żuławy water works both ways

Żuławy is polder land, cut through with drainage canals, so managing water here means two things at once: bringing it in during a drought and taking it away when there is too much. Our mada soils are high in humus and hold moisture better than light soils, which we write about in our post on [Żuławy mada soils](/blog/gleby-zulawskie-mady-pod-cebule). That helps in a dry week, but it comes back at us in downpours, because the water has nowhere to go quickly.

The 2025 season showed this literally. In July we had 150 to 220 litres per square metre in a single day. The result was flooding, drainage canals overflowing, compacted soil and a weaker finish to the yield, and on top of that heavy pressure from secondary weeds, because onions keep the soil profile bare all season long. So our water plan for the crop is not just the irrigator, but also clear ditches and knowing where the water stands longest.

{% callout tone="warning" %}
Too much water late in the season does more harm than a slight shortage. An onion that gets watered then ripens later, does not close its neck and stands up worse to storage. So the last decision of the season is to cut the water off, not to add more.
{% /callout %}

## What irrigation gives the onion buyer

An evenly irrigated crop gives an even batch, and an even batch means less work and less waste for the buyer. The onions come out close in size, so they hit the ordered grade more easily, fewer bulbs drop out at sorting and fewer end up in a lower class than planned. Then there is storability: a ripe onion with a closed neck sits quietly in our store for 13,000 tonnes, so we have it for buyers all year round, not only after harvest.

We manage water with the same logic we run the whole farm on: by the principles of Integrated Plant Production and free of pesticide residues, with every batch tested. We describe the whole growing cycle, from sowing to harvest, in our guide to [how we grow onions in Żuławy](/blog/cebula-z-zulaw-jak-uprawiamy). If you are looking for an onion supplier, see our [onion offer](/oferta/cebula) or write through the [contact page](/kontakt), and we will give you the available grades and dates.

## Frequently asked questions

### How much water do onions need in a season?
The accepted figure is 300 to 500 millimetres, counting rainfall and irrigation together. At peak growth that is around 3 millimetres a day, and a single pass with the irrigator usually delivers about 20 millimetres. The exact amount depends on the soil and on how the season runs.

### When does irrigating onions matter most?
From mid June to the end of July, that is during bulbing. This is when size and tonnage are made, so a break in the water supply hits the yield directly. The second important moment is emergence, because even moisture gives an even batch.

### When should you stop irrigating onions before harvest?
At the end of the growing season, when the onions are meant to ripen. Water at this stage delays the tops going over and the skin closing, and the onions stand up worse to storage. We cut the water off and wait for ripeness.

### Do you have to irrigate onions in Żuławy?
Yes, even though mada soils hold moisture better than light soils. Onions have shallow roots and will not reach water in the deeper layers, so a few dry days during bulbing can take away part of the yield. In Żuławy there is a second problem: in downpours the water has to be taken away fast.

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Want to know what actually comes off a hectare in a crop like this? Have a look at our post on [how much onion we harvest per hectare](/blog/ile-cebuli-z-hektara), or write to us through the [contact page](/kontakt).