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Top Problems Growing Onions and How to Fix It

As an onion grower, there is nothing more bewildering than taking great care of your plants, only to get tiny or deformed onions when harvest time comes around. In fact, this is one of the most frustrating experiences for home veggie gardeners. The good news is that having a knowledge of a few simple onion facts could make a massive difference in your harvest.  

Some of the top problems you may encounter growing onions include stunted growth, discolored leaves, wilting or droopy plants, and malformed bulbs due to poor soil, pests, onion diseases, or adverse weather conditions.  

This article will reveal the most common problems home veggie gardeners face when growing onions. In it, you will also discover effective ways to fix any onion growing problems so that you can harvest large, firm bulbs that are packed full of delicious flavor. 

Onion Not Growing

When looking at all the possible reasons why your onions fail to grow healthy and large, the first thing you must consider is the climate in your area. Where you live determines the types of onion varieties that you can grow successfully. It’s also a major factor in whether you need to start with seeds, sets, or onion transplants. 

  • Onions, particularly those grown from sets, are usually low-maintenance and trouble-free. 
  • Seed-grown onions tend to have more issues due to being sown directly and staying in the same position for longer. 
  • If you start them in modules and then transplant them, seed onions can also be just as dependable as sets. 

Growing the wrong type of onion will result in a smaller, less satisfying harvest. If you want to find out more about how to choose the right onion variety for where you live, check out this article, which explains the topic in detail. 

Once you’ve established that you’re growing the right onion variety that is compatible with your climate, it’s time to look at other problems that might affect your crop.

Onion Turning Yellow

Poor soil is one of the main reasons why your onion plants may be turning yellow. It could also be responsible for small onions. Whether due to competition, a lack of essential nutrients, or an imbalance in the pH of the soil, this is a condition that must be remedied if you hope to harvest a healthy, flavorsome crop. 

Reduce Competition – If the issue is competition, you need to space the onions at least 4-5 inches (10-12cm) apart. Close spacing of plants leads to a significant decrease in the size of the bulbs. Allow 12-18 inches (30-45cm) between rows. Alternatively, you can space onions about 6-8 inches apart (15-20cm) in all directions.

Loosen Soil – You also need to make sure that the soil is loose in order to provide the ideal conditions for growing healthy onions. Tightly-packed soil makes it difficult for the plants to move, resulting in bulbs that are stunted or deformed.

Increase Nutrition – If the problem has to do with nutritional deficiencies, such as manganese, for instance, it will damage the onion leaves, causing them to change color and curl up. The necks become thicker, and the bulbs don’t form for a long time. 

The tips of the leaves may begin to burn, and the onion’s growth could become very slow. An effective way to combat different types of nutritional deficiencies is by mixing in a high-quality, balanced fertilizer or compost to your soil at the start of the season. You can also use a high-nitrogen fertilizer as this will help to promote new growth in plants. 

Just keep in mind that it is possible to over-fertilize the onion plants. This is particularly true if you use too much of the fertilizer at one time. 

Balance Soil pH – When there is a problem with the acidity and alkalinity of the soil, the plant suffers. Extreme pH levels prevent the plants from absorbing the nutrients in the soil, resulting in a deficiency even though the nutrients are available. You can tell by the color change of the leaves. The solution, in this case, is to adjust the pH to the proper levels. 

  • If the levels are too high, you fix it by amending the soil using sulfur or organic substances, like old leaves and plant debris. This will lower the pH and boost the soil acidity. You can also use ammonium sulfate or any other fertilizer that increases acidity. 
  • If the pH levels are too low, you can make the soil more alkaline by treating it with wood ash or adding lime (calcium carbonate). This will raise its pH to the desired levels. Just keep in mind that adjusting soil is a process that takes time. You may need to perform multiple treatments before achieving the desired outcome. 

Onion Seedlings Turning Yellow

Onion white rot could be the reason why your onion seedlings are turning yellow. It is a nasty fungal disease with spores that can survive for up to fifteen years in the soil. Because of this, normal crop rotation is not an effective deterrent for this onion disease. The fungi are easily transferred across patches of soil on shoes and garden tools. 

This dreaded fungal disease causes white mold to form at the plant’s base. This ruins it for eating and storing. The white-rot pathogen can also cause wilting of the leaves and leaf dieback. Once onions contract this disease, there is nothing much that can be done. There is currently no cure available to gardeners. 

The only effective management or controls of onion white rot are avoidance and sanitation

  • If your onions are infected, you need to dispose of all affected plants either in the rubbish bin or in your local bio-digester if there’s one near you. 
  • Alternatively, you can incinerate them, but you must make sure all the plants are burnt to ash. 
  • Never compost plants that were exposed to white rot. Spores could survive and spread the problem throughout your garden. 

Since you will be unable to grow onions on the infected soil for up to a decade and a half, you must consider other alternatives, such as planting your onions in a completely separate patch of land. Another option is to construct a deep raised bed then fill it with clean topsoil and compost. 

Onion Turning Brown

Fungal diseases are among the main causes of onion leaves turning brown. The leaves gradually die back all the way down to the bulb. In addition to white onion rot, other fungal conditions include rusts, mold, smut, white leaves, and downy mildew. Each of these diseases results from weather conditions that are too warm and humid. 

Onion plants are significantly more susceptible when there are high nitrogen levels in the soil. To deal with this problem, try adding a high-potash fertilizer, such as tomato feed, when you first notice your onions turning brown. This will alter the nutrient balance and possibly help turn things around. You can also try using anti-fungal sprays from your local gardening center. 

However, it’s important to note that once infected by any of the fungal diseases mentioned above, it’s usually too late for the crop. As with onion white rot, the only effective management at that point is simply avoidance and sanitation. 

Onion Seedlings Wilting

Thrips – Thrips could be the cause of wilting onion seedlings. These tiny insects are extremely hard to see, often hiding inside the angles between the bulbs and leaves. They feed on the underside of the onion leaves, causing them to wilt and turn a silvery color. 

If left unchecked, these tiny mites can affect the entire portion of the plant that is above ground. If your onion crop is infested, you can try using pesticides to get rid of them. Pesticide use and general recommendations for different areas are constantly changing these days. Make sure you check with your local agent for the most current recommendations. 

Cutworms – If you notice any cut, missing, or wilted onion plants, cutworms could be the problem. Cutworms are caterpillars that eat away at the leaves of your plants. They hide in the soil and come out to feed at night. They affect the portion of the onion plant that is above ground, and when plants are infected, they tend to wilt and change color. 

Cutworms are usually found moving up and down by the soil moisture line. If the surface of the soil is dry, the worms move a couple of inches beneath the surface, where they can find moisture. After the garden is watered, they move back to the surface. 

  • To prevent the problem of cutworms, you can put cardboard collars around your new transplants, extending 1-2 inches (3-5 cm) above and below the soil level. This will stop them from reaching your tender plants. 
  • If they are already on your onions, you can use non-toxic methods, such as picking them off and dropping them into a bucket of soapy water. 
  • Alternatively, you can get rid of these frustrating pests by using chemical pesticides or Bt (Bacillus thuringiensis), a naturally-occurring bacterium that targets various caterpillar-type pests.

Onion Plants Dying

Fluctuating temperatures and conditions are yet another problem gardeners have to contend with. Temperature stress can cause early flowering, which usually results in extremely small onions. When temperatures change quickly from one end of the spectrum to the other, the damage affects the entire onion plant. 

Strong sunlight and high heat kill plant tissue, and older plants usually get burned. Onions are just as susceptible to the harsh cold as they are to intense heat. When temperatures drop below -5℃ (23℉), young plants die, and bulbs get damaged, turning gray and soggy. 

Temperature Stress – There are ways of controlling the temperature to prevent it from getting too hot or too cold. You can use freeze prevention and protection as well as a protective cover like Purshade, which reduces solar stress in crops while allowing photosynthesis to continue. These two effective techniques can save your onion plants from dying from temperature stress. 

Hail and Storm Injury – Another reason why your onions may be dying may be due to hail and storm injury. When rain is combined with strong winds, onion plants often incur damage. The stalks and leaves of the plants are broken and torn by the physical impact. This weakens the entire plant, which, in turn, increases its chances of getting infected. 

Since it’s impossible to control weather conditions, there isn’t much that can be done about this condition. 

Onion Plant Drooping

One of the main reasons for drooping onion plants is the lack of adequate water. You need to ensure that your onions are watered properly for healthy growth. Too little or too much water can have an adverse effect on your crop. You must avoid letting the soil become bone dry, so make sure you feel the ground around your onion plants each day to see if it’s dry. 

Follow these steps when watering your plants to ensure optimal hydration: 

  • Water your onions in the mornings when temperatures are still cool. This helps to prevent the sun from evaporating the water too quickly before your plants have had a chance to drink their fill. 
  • Don’t water your onions at night. If the soil in your garden stays wet for too long, it could cause root rot, which could stunt your plants’ growth or even kill them outright. 
  • Avoid getting water on the onion leaves when watering your plants. Moisture on the leaves can cause fungus diseases to infect your onion bulbs. Monitor the weather forecast in your area and don’t water your plants if rain is expected. 

Onion Not Sprouting

If your onions are not sprouting, onion fly maggots could be the cause. These destructive pests are among the most prevalent onion growing problems. They attack an onion by laying their eggs at their base. The eggs hatch into maggots, which then eat through to the roots, causing the onion to stop growing or killing it outright. 

This happens fairly quickly, which is why it’s important to identify and deal with this issue as soon as possible. Identifying onion fly maggots is pretty straightforward. Look for drooping and yellowing leaves or onions that are not sprouting. Smaller onions tend to die first, and larger onions stop developing and start to look sickly. 

To confirm the presence of onion fly maggots, lift the onion plant and look for small maggots at its base, as well as in the soil where you lifted it from. Since there isn’t currently any effective chemical cure for these pests, the only defense is to prevent them from accessing your plants by covering the ground with fleece. 

Onion fly maggots rarely attack set-grown onions. This is because they find the plants using smell, which is most potent when thinning direct-sown onions. 

Onions Not Producing Bulbs

When an onion stops directing energy into the bulb and grows the stalk and flowerhead instead, this is known as bolting. This behavior is easily triggered in sets by early periods of low temperatures that are followed by warmer temperatures later in the day. 

Bolting is also triggered when miss-aimed hoeing or loose soil causes root disturbance that convinces an onion plant that it’s dying and therefore needs to propagate. This process is rare in seed-grown onions, but it can be up to 40% of a set-grown crop. 

Large sets are more susceptible to bolting, so don’t disregard smaller sets in favor of larger ones, as so many gardeners do when planting out. In order to help fix the problem of bolting in sets, some merchants use a method of treating sets to kill off the embryo that produces the flower. 

The best way to keep onions already planted in your garden from bolting is to protect them from stress. There isn’t any cure for this condition, and once the plant has bolted, all you can do is to cut off the stalk that is developing as soon as you notice it. You should also note that although such onions may be edible, they will not be suitable for storing. 

Onions Rotting

The first thing to check for rotting onions could be caused by poor soil. If there isn’t adequate drainage, the soil will stay wet for longer, leading to root rot. This results in stunted growth and could even cause the plants to die. If you have an issue with wet soil, it’s important to address it as quickly as possible. 

  • Water your plants in the morning.
  • Don’t water your plants if the ground is still wet or if rain is expected.
  • Don’t water your plants at night. This promotes root rot since the ground remains wet for much longer than it would if you watered your onions in the morning. 

Final Thoughts

Now you know the top problems growing onions and how you can deal with each of them. Use this article as your guide to help you take the necessary measures to keep your onion crop growing healthy and strong. 

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