Watering Onions (How Often & Tips)

Like most garden plants, onions require less water in the beginning of their growth and more as they become bigger plants and start to develop bulb size. Also like many garden plants, regular watering when it’s needed will result in optimal and steady growth of the onion plant.

Research and extension trials in Georgia have indicated that properly irrigated onions will yield 25 to 50 percent more than dry land onions. Irrigated fields typically yield a higher percentage of jumbo bulbs, which generally bring a higher price on the market. Irrigated onions are sweeter and less pungent than dryland onions, which is especially important for Vidalia onions.

University of Georgia Extension – Onion Production Guide

Onion plants require amounts of water varying from ½” – 2” a week from the time they are first planted in the ground until they begin to show signs of reaching maturity.  They should be watered with 0.5″ of water at a time during early growth and 0.5″-1″ of water at a time once bulb growth starts.

The figures above include rainfall. We use wunderground to get expected rainfall amounts. Use a rain gauge with a wide mouth to get an accurate rainfall measurement.

How Often To Water Onions

During the beginning of the season, onions need about ½” – 1” of water weekly, but that amount will increase to 1.5″-2” a week during bulb formation. 

When onions are planted, the length of the growing season, and when bulbs begin to form vary depending on what area you’re gardening in.

The region you’re gardening in will dictate the variety of onion being grown and the length of daylight needed to initiate bulb growth. Check out “Long Day Onions vs. Short Day Onions” for more on that.

Once bulb growth is initiated by the daylight hours growing longer and hitting the necessary mark more water is needed by the plant.

Watering should be done first thing in the morning.  This will allow the onion plant to absorb the most water and allow time for foliage to dry. 

If watering is done midday water evaporates in the heat, both in the air and from the topsoil, and not as much is absorbed by the plant. Early evening is the second best time to water.

Late evening watering doesn’t leave enough time for the plant to dry out before nightfall, which can lead to disease like powdery mildew.

When Should You Stop Watering Onions?

Onion plants no longer need to be watered once they start to show signs of reaching maturity.  The tops of the onion plants will begin to yellow and fall over – that’s the sign to stop the weekly watering schedule. 

Watering after this point can cause delays in the curing of the onion bulbs and can lead to rot and storage issues. This will also allow the onion bulb to concentrate flavor and sugar levels.

Onion Plant Watering Tips

  • Onion plants foliage don’t usually wilt when it needs to be watered. To check if the soil needs to be watered the best method is to feel the dirt 3″-4″ down. Soil is not just wet or dry but somewhere in between. Run the soil between your fingers and feel the texture. If it’s mostly wet let it be, or if it’s mostly dry water.
  • Onion plants need more water when they get bigger and start to develop bulb size. They also need more water in hotter weather.
  • Water onion plants in the early morning or early evening.
  • Stop watering when onion plant leaves start to yellow and fall over.

Check out “Onion Plant Care & Growing Tips” for more tips on growing onions.

Watering Methods

The method used to water the onion plants plays an important role in how often and how much water is needed. 

Using a hose and/or sprinkler for watering requires about 1” of water twice a week depending on rain and how well the soil drains.  When using this method, it is extra important to try and water early in the morning or in the early evening. Excess water on the onion foliage can lead to disease in the plants.

Drip irrigation is the most efficient watering system as water is delivered directly to the bottom of plants. It takes the initial time to set up but after that it’s a breeze to water.  When using this method, watering frequency is usually increased to every 1-2 days but with a smaller amount of water given, about ½” of water each time.

The furrow method of watering is an option.  Onion rows should be planted 12” – 24” apart and this leaves adequate room for the furrows to be dug.  The furrows should be flooded once or twice a week.

Do Onion Plants Need a Lot of Water?

1” – 2” of water once or twice a week is what onion plants need in order to produce high yields and full sized bulbs.  During the weeks when the onion bulbs are growing is when the plants will need the most water. 

The soil needs to be moist but no standing water. Standing water is a sign of poor drainage or a low point in the garden where onions can die from root rot.

Onions that do not get enough water can have problems with bulb formation, causing them to split or have a more bitter flavor.  Giving the onions water when they need will lead to bigger & sweeter onions.

Getting Jiggy, I Mean Scientific, With It

Feeling the soil to determine how much moisture is in it is a common garden practice. However, it is possible to install soil moisture meters that will give a reading of soil moisture levels.

There are also bundles that have soil moisture meters linked to automatic water hose hookups to automate the watering process.

Install soil moisture sensors at two depths, one near the middle of the root zone and one near the bottom. Common practice is to install one at four to six inches and one at 10 to 12 inches. The ideal range for soil moisture is between (soil tension) 5 and 20 centibars for most coastal plain soils. Readings of less than five indicates saturated conditions and above 20 indicates the soil is becoming dry.

University of Georgia Extension – Onion Production Guide

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