Although tomatoes are the most common crops in most kitchen gardens, they are also the most troublesome, especially because they can play host to a wide range of pests and diseases that can leave you counting huge losses.
One of the most common problems with tomatoes is the yellowing of leaves. Why do tomato leaves turn yellow and how can you deal with this problem? This article talks about the causes of tomato leaves turning yellow and the best remedies.
Why Are the Tomato Leaves Turning Yellow?
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There are many reasons why your tomato leaves are turning yellow. Sometimes it could be due to bad weather and in other cases, it could be a symptom of an underlying health problem. Here are some of the common causes of yellow leaves in tomatoes.
1. Watering Problems
Most cases of yellowing of tomato leaves are a result of incorrect watering. Most tomato growers do not know how to water their plants properly. This problem can occur if you don’t give your tomatoes enough water or even when you give them too much water.
So, if your tomato leaves have started to turn all of a sudden, make sure you are watering them correctly.
If you give your tomatoes too much water, it will suffocate their roots, causing them to rot. With the damaged roots and inadequate oxygen in the soil, the leaves will suffer from oxygen deficiency, causing them to turn yellow and fall off. under watering your tomatoes can also cause their leaves to wilt and turn yellow.
If your tomatoes aren’t getting enough water, their leaves will start to turn yellow from the edges and continue to wither until they fall off.
2. Soil Compaction
If the soil around your tomato plants doesn’t have enough ventilation, the roots will suffocate due to a lack of oxygen. And if the roots cannot transport oxygen, water, and nutrients to the rest of the plant, the leaves start to turn yellow and eventually the entire plant dies.
Soil compaction happens when soil particles are hard-pressed, reducing pore space between them. With reduced pore space within the soil, the bulk thickness increases, preventing the roots from getting enough oxygen. Soil with large amounts of clay and sludge naturally has more pore space, which lowers its bulk density.
Compacted soil has a reduced rate of water penetration and drainage because its small pores cannot effectively move water downward through the soil. Moreover, the circulation of gases in compacted soil is significantly reduced, causing aeration-related complications.
3. Transplant Shock
If your recently transplanted tomato seedlings have started to turn yellow, it could be due to transplant shock. This usually happens when you move your seedlings from a warm nursery, such as a greenhouse or an indoor nursery, to a cold outdoor garden. In this case, the seedlings will need some time to adjust to their new environment.
This type of discoloration usually happens to the bottom leaves of the plant. Luckily, this problem is just a short adjustment phase that will resolve itself after a few days. As long as the emerging leaves are green and healthy, you can take it easy because the yellow bottom leaves will fall off, allowing the plant to continue to grow.
Several tomato plant diseases cause the yellowing of tomato leaves. Unfortunately, most of these diseases are hard to treat once they start to show these symptoms. The first one is the early blight, which is caused by a fungus in the soil.
Early blight is very easy to identify. It starts with pale-yellow spots in the lower leaves that eventually turn into dark-brown patches with yellow lines at the edges. If this disease is left untreated, the leaves will turn yellow and fall off.
Another common tomato plant fungal disease is the septoria leaf spot. This disease causes large brown spots in the leaves that are connected with yellow patches. If not treated immediately, this disease will spread to other parts of the plant, including the stem, causing the entire plant to die.
Yellowing of leaves in tomatoes can be a result of a variety of wilts, including fusarium wilt, bacterial wilt, and verticillium. The fusarium wilt starts from the soil by infecting the roots, preventing the movement of water, oxygen, and nutrients to the stem and leaves. The affected tomato plants will look wilted even after watering them routinely.
Their leaves will drop off one by one starting with the bottom leaves. Tomato plants infected with verticillium wilt show the same symptoms as early blight and septoria leaf spot. It starts with the lower leaves developing pale-yellow spots surrounded by brown veins. As it progresses, the spots turn brown and the leaves will eventually fall off.
The bacterial wilt is caused by a bacterium commonly found in moist sandy soil. This disease usually starts after transplanting but it doesn’t show any signs until the seedlings are fully established. This type of wilt causes the leaves to suddenly turn yellow.
5. Nutrient Deficiency
If none of the above reasons explains why your tomato leaves are turning yellow, you need to check if the plants are getting enough nutrients. Nutrient deficiency occurs when the soil lacks a particular macro or micronutrient that is needed by the tomato plants. It could also be an issue with the plants’ ability to absorb the nutrient.
The most common macronutrient that causes yellowing in tomato leaves is nitrogen. Without nitrogen, the plants’ development will be stalled and the older leaves will turn pale-yellow. So, if your tomato plants stop growing after developing yellow leaves, check if they are getting enough nitrogen.
The only way you can be certain that the cause of yellow leaves is nitrogen deficiency is to conduct soil tests. A test will reveal the real cause of the problem, allowing you to find a targeted solution.
Should You Remove Yellow Leaves from the Tomatoes?
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As your tomato plants continue to grow, their lower leaves will (the leaves below the first set of flowers) will start to turn yellow and dry out. This normally happens when the plants reach 12 to 18 inches in height. There is no harm in removing these leaves provided they are below the first set of flowers.
Removing dead or yellowing leaves from a tomato plant doesn’t have any effect on the plant. But you should be careful when removing these leaves not to leave a big wound on the plant.
However, some indeterminate varieties of tomatoes can benefit from removing the yellowing or dead leaves because they can bloom and set fruit severally in a single season.
How to Fix the Problem of Yellowing Leaves in Tomatoes
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To deal with this problem successfully, you have to know the cause. Once you understand why it is happening, it will be very easy to fix it. But here are some of the simple ways to address the problem of yellowing leaves in tomatoes.
1. Improve Your Watering Habit
If incorrect watering is what is causing your tomato leaves to turn yellow, learn how to water them properly. For instance, don’t water your tomatoes when the top layer of the soil is still wet or when the soil is waterlogged.
If your tomato plants are still struggling to grow upright and their leaves are wilting, it means you are underwatering them.
So, don’t forget to water your tomatoes. Always check your soil to make sure it’s not dry or waterlogged. Only water your tomatoes when the top 1 or 2 inches of the soil is dry. The best time to water your tomato plants is in the morning to avoid evaporation or damage to the leaves.
When watering your tomato plants, focus on the soil around their roots, not the leaves. Also, water them slowly and deeply so that the soil is fully saturated to encourage the roots to grow deep.
2. Aerate Your Soil
If lack of aeration is the cause of yellowing leaves, check how well your plants’ roots are established in the soil and use your hands to loosen the soil for improved aeration. While this remedy works, it can easily cause damage to the root system.
Therefore, the best remedy is to ensure that the soil is properly aerated before planting the tomatoes.
Make sure the soil in your garden is enriched with all the necessary nutrients, minerals, and organic matter to avoid compaction. Also, don’t walk on the soil regularly to avoid compressing it. You can also avoid soil compaction by growing your tomatoes in elevated beds or wide pots.
3. Warm Your Soil
As mentioned above, your tomato leaves will turn yellow when the seedlings suffer transplant shock. Although this shock doesn’t affect your plants’ development, you can avoid it by warming up your soil before transplanting the seedlings. Also, make sure that night temperatures in your garden do not drop below 50F.
If your seedlings are showing signs of transplant shock, you can help them to recover from the shock quickly by removing the yellowing bottom leaves. This helps to focus more energy on the new growth.
4. Treat the Diseases
If the yellowing problem is the result of any of the common diseases, treat them immediately. These diseases should be treated as early as possible so that they do not spread to other parts of your plants and garden. Most of these diseases can be managed if discovered and treated early.
Remove all the affected leaves and throw them away from your garden. Treat your plants with a fungicide that is designed for a specific disease, and make sure you follow the instructions offered by the manufacturer.
If you discover any of the wilts in some of your plants, remove the affected plants from your garden immediately because there is no cure. Discarding them early helps to prevent the wilts from spreading to healthy plants.
You can also avoid these diseases by choosing a variety of tomato plants that is highly resistant to diseases, and space your plants properly.
Also, make sure your gardening tools are properly cleaned after every gardening session to avoid spreading diseases. Most of these diseases can be prevented through crop rotation, which keeps the soil healthy.
5. Add Nutrients to the Soil
If your tomato leaves are turning yellow due to a lack of nutrients, you should test your soil to know which nutrients and minerals are lacking. Once you identify the missing nutrients, apply an all-purpose fertilizer to offset the deficiency.
What Should You Do to Prevent Tomato Leaves Turning Yellow?
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Although it is not possible to prevent the problem of yellowing of leaves in your tomatoes altogether, there are several important steps that you can take to minimize the risk.
• Use disease-free seeds – even though there is no evidence to show that most of the above-mentioned diseases can be carried by seeds, it’s always good to err on the safe side. If you are planting seeds from your previous harvest, make sure they are not infected and process them thoroughly to remove any infections.
• Clean your garden first – before transplanting your seedlings, clean your garden completely and warm it up. Remove weeds, debris, and diseased plants before transplanting your seedlings.
• Avoid overhead irrigation – water on the leaves will aid the spread of serious diseases like the Septoria leaf spot. So, direct the water only to the base of the plant.
• Space your plants properly – space your tomato plants properly to allow enough airflow and stake them to prevent them from touching the ground.
• Add a layer of mulch – mulching below the plants helps to keep the soil soaked and prevent the bacteria on the ground from getting splashed onto the leaves.
Now that you are aware of the reasons behind your tomato leaves turning yellow, it should be easy to fix the problem if it occurs in your garden or even avoids it altogether. But remember that this is a trial and error exercise. So, if one fix doesn’t work, try another one until you succeed in restoring health to your tomato plants.
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