When to Stop Watering Onions

Stop watering onions at the end of the season when the green leaves fall over. Plan to give your plants one to two inches of water per week throughout the rest of the season. Onions need even more water during the seedling stage. During that time, it’s wise to check their watering needs daily. Try to avoid overwatering by checking the soil with your finger before adding water. If your onions get too much water, the leaves turn yellow and the rest of the plant rots away.

How Often Should You Water Onions?

Plan to water your onions once a week unless it’s been raining. Onions need at least one inch of water per week, if not two, especially if the sun is drying up the soil. So, give them about ½ to 1 gallon of water per square foot to keep the soil moist. Add straw mulch around your onions if your soil dries out too quickly.

• Onions grow best when given water once per week.
• Aim for one to two inches of water per week, or 1/2 to a full gallon per square foot.
• Straw mulch can help the soil retain moisture and dry out much less quickly.
• Check the moisture content of the soil with your finger before watering.

You should check the soil’s moisture content before watering. Push your finger about an inch or two into the soil. If the soil feels dry to that depth, give your plants water. Soil moisture meters, like this one, can also be used to keep track of your onion’s soil conditions.

Do Onions Need to Be Watered Every Day?

Only water your onions daily during the seedling stage. During that time, the soil must stay completely moist every day. Otherwise, your onion seeds will die before they have a chance to grow their full root system.

• Only water daily if you are growing onions from seed.
• Keep the seedlings’ soil moist to the touch with one cup of water per day.
• Decrease watering sessions to once per week as soon as bulbs start to grow.
• Most onions start the bulb development stage after 30 to 60 days.

Onion water needs change as they begin to grow. Dial back your watering sessions to once a week as soon as you see signs of bulb growth. Most onions move from the vegetative growth stage to bulb development within a month or two.

How Do You Tell If Onions are Overwatered?

Overwatered onions quickly develop yellow foliage. The tops will soon fall over if the plants keep getting too much water. The onion bulb and roots will then begin to rot, unless the plant can fully dry out. Once the rot sets in, you cannot salvage your onion plants. It’s important to act fast as soon as you see signs of overwatering in your onion bed.

• Yellow, unhealthy-looking leaves, falling over bulbs and roots are signs of early rot from overwatering.
• Onions cannot recover from rotten bulbs and roots.
• Stop watering your onions to give them time to recover from the overly moist conditions.
• Stop watering and build a hoop house or drape plastic sheeting over the beds to protect onions from the rain.

Do not add any more water when overwatering is present in onions. Wait until the leaves start to look healthy again before giving them more water. If rain is expected, use these plant covers to keep your onions dry.

Can Onions Tolerate Wet Soil?

Onion seedlings love moist soil, but wet conditions are much harder for onions to tolerate when they’re in the bulb development stage. Most onion varieties need one to two inches of water per week to grow big bulbs and healthy foliage.  

• Only onion seedlings love consistently wet soil.
• During the bulbing stage, onions do not tolerate wet soil very well.
• Never let the soil dry out to the point that it cracks around the onion bulbs.

On the flip side, because onions have a shallow root system, you cannot let the soil get to dry. The soil shouldn’t ever look dry and cracked around the base of the plant. Dry conditions around onions are an indication that it’s time to water. Try to achieve a good balance with your watering approach to keep your plants growing strong.

When to Stop Adding Water to Onions

Stop watering onions as soon as the season ends and their green leaves fall over. Then, wait until the foliage dries up to harvest the bulbs. Throughout the rest of the season, water onions once per week. Give your onions one to two inches of water at each watering session.

• Onions no longer need water when their leaves fall over at the end of the growing season.
• Overwatering onions results in yellow leaves and rotten bulbs and roots.
• Allow overwatered plants to recover by withholding the water until the leaves look healthy.

Watch for signs of overwatering, like yellow leaves and dying foliage. Overwatering will cause the bulbs and roots to rot if it continues. Plants can recover if allowed to dry out until the leaves look healthy again. 

Onions take about 100 to 150 days to reach full maturity. During that time, water problems can wreak havoc on your harvest. So, take it day by day and do all you can to keep your plants at just the right moisture level.