Onions are often billed as easy-to-grow vegetables because they grow in nearly any well-drained soil and have few issues with garden pests. In addition, they can be tucked into unused sections of the garden, too. However, to grow large, flavorful bulbs, you must provide your onions with water and nutrients. Find out how and when to water your onions to promote optimal growth.
How often to water onions
Onions have shallow root systems, meaning they need plenty of moisture in the top few inches of soil. They typically do well with 1 to 2 inches of rainfall a week. If Mother Nature doesn’t cooperate and you suffer a dry spell, you will likely need to water your onions once or twice a week during the summer.
Check the soil frequently and water your onions if the soil feels dry 1 inch below the surface. Remember, the soil should be kept moist but should not be soggy. Soggy soil will cause your onions to rot.
What is the best time of day to water onions?
The best time to water onions is early morning before it heats up for the day. This prevents water loss to evaporation as you water them. If early morning is not convenient for you, water your onions in the late afternoon after it has cooled off for the day. If you must water your onions in the evening, do so early enough that the foliage dries before dark. Wet foliage at night encourages disease.
Avoid watering your onions when it is windy, as this also causes water loss as the droplets are carried away in the wind.
Watering in the morning gives your onions the moisture they need to meet the day’s demands. Watering in the late afternoon restores water lost during the day and allows your onions to rejuvenate during the night.
Signs my onions need water
- Dry Soil: The easiest way to tell if your onions need watering is to check the soil. Stick your finger into the soil. If it feels dry 1 inch below the surface, your onions need to be watered.
- Wilted Tops: Like all plants, onions need adequate water to maintain turgor — the pressure inside the plant cells that keep foliage rigid. If they do not receive enough water and the pressure drops, your onion leaves will wilt. Wilted onion tops may flop over onto the ground.
Signs of overwatering onions
- Soggy Soil: Onions need adequate water to grow and prefer moist soil that does not dry out completely. But they cannot grow in soggy soil. If the soil around your onions feels wet and soggy, you are overwatering your onions.
- Yellowing Tops: Overwatering causes the soil to become saturated and chokes out oxygen to the roots of your onions. The tops may react to the stress by turning yellow or developing brown tips.
- Wilting: Because the roots of overwatered onions cannot get the oxygen they need, they cannot uptake water and nutrients to perform normal plant processes. Foliage may wilt, similar to wilted foliage due to lack of water.
- Soft or Rotting Onion Bulbs: Overwatering onions can cause the onion bulbs to rot in the soil. If the bulb begins to rot, the condition cannot be reversed.
How deep should my soil be wet?
Onions have shallow root systems that only reach a few inches into the soil. You need to keep the soil moist to the root level to keep your onions healthy. That means it’s best to keep the top 3 to 4 inches of soil moist.
Do you need to mulch onions?
Onions will grow without being mulched, but mulching is a great way to keep the soil moist and prevent it from drying out too quickly. Place a 2 to 3-inch layer of straw or grass clippings around the onion bulbs. This helps hold in moisture and suppresses weeds, too.
Do I need to stop watering onions before harvest?
Onion foliage yellows and eventually dies back when they mature. Because the plants are no longer growing, they no longer need water. Stop watering your onions when the foliage turns yellow and flops over. Allow the tops to dry before harvesting your onions.
Why don’t my onions form big bulbs?
There are several reasons for onions failing to form large bulbs. The most common are:
- Lack of Fertilizer: Onions prefer nutrient-rich soil. Amending it with compost or well-rotted manure in the spring will boost nitrogen and phosphorous. Phosphorous is vital for bulb development. If you use commercial fertilizer, choose a balanced fertilizer like 10-10-10 or one higher in phosphorous than nitrogen, such as 5-10-10.
- Lack of Water: Water is essential for plant growth. A lack of adequate water will inhibit plant growth and may result in small onion bulbs.
- Not Enough Sun: Onions are sun-loving veggies and need at least 6 to 8 hours of direct sunlight a day to flourish. If possible, plant them where they receive all-day sun.
- Too Many Weeds: Onions have shallow root systems and cannot compete with weeds with more extensive roots that may rob them of the nutrients they need to thrive. Weeding the onion patch regularly is necessary for your onions to flourish.
- Planting at the Wrong Time: Onions need to be planted in the early spring to give the foliage time to get big before the bulbs begin to form. They should be planted as soon as the soil can be worked. Planting them too late in the season may result in large foliage but prevent them from forming large bulbs.
- Planting the Wrong Type of Onion for Your Region: Onions respond to the number of hours of daylight to start bulb formation. Onions are classified as long, short, and neutral day onions. Long-day onions need between 14 and 15 hours of daylight to start forming bulbs. Short-day onions form bulbs when they get 10 hours of light a day. Neutral Day onions form bulbs regardless of the number of hours of daylight, explains Bonnie Plants. It is essential to choose an onion variety that is suited for the amount of light you receive in your region.
Growing onions in the home garden can be rewarding and doesn’t require a lot of work. However, you should exercise care when it comes to watering them. Too much or too little water can compromise the health of your onions. The easiest way to tell if your onions are getting the water they need to thrive is to check the soil frequently and water them when the soil feels dry to the touch 1 inch below the surface.