No one likes to see tomato leaves turning yellow! There are a few things that cause this problem in your garden.
I went out into my garden and found some tomato leaves turning yellow, and my heart sank a bit.
I know that’s a bit dramatic, but I’ve struggled in previous years to grow tomato plants properly with large harvests. This year seemed like MY year, and yellowing leaves means something is wrong, even if it’s minor.
Thankfully, my problem ended up being a nutrient deficiency that I was able to fix, but it doesn’t always turn out that way. Several causes lead to tomato leaves turning yellow, and if you notice it in your garden, you have to troubleshoot and determine which if the reasons is the culprit in your garden.
Let’s take a look at some of the top reasons that your tomato plant leaves might turn yellow.
10 Reasons for Tomato Leaves Turning Yellow
1. Transplant Shock
Sometimes you might notice tomato leaves turning yellow right after you transplant them into the ground. This happens in the early spring when the nights aren’t too warm.
Try not to panic because this is a transplant adjustment period. Within a week or two, the leaves should go back to green again, but make sure you snip off the yellow tomato leaves off the bottom of the plant. Watch to make sure your plant is producing healthy leaves at the top of the plant.
2. Watering Problems
Tomato plants need proper amounts of water, but if you give your plants too much or too little water, it will result in tomato leaves turning yellow. The soil around your tomato plants needs to dry out between watering, and the soil should never be soggy.
More often than not, gardeners give their plants TOO much water. Everyone knows that lack of water is seriously problematic for plants, but shouldn’t abundant water be okay too?
Too much water makes it hard for the soil to properly drain it away from your plants. Then, the roots end up submerged in water, leading to rotting and other problems. It also dramatically increases the risk of fungal diseases, and the excess water reduces the oxygen available for the roots, essentially suffocating them.
Always make sure you check the soil with your finger before watering. All you have to do is put your finger into the soil two to three inches down. If the soil is damp, then you don’t need to water, but if the soil is dry, it’s time to water.
Tomato plants always need to be watered at the base of the plant. Keeping the foliage as dry as possible is essential to prevent diseases.
3. Non-Aerated – Compacted – Soil
If you have compacted soil, it can be a real problem. One of the keys to large, healthy tomato plants is a large, robust root system that anchors the plant and delivers nutrients and water throughout it. When you have compacted soil, water, nutrients, and air struggle to reach the roots.
Fixing compacted soil AFTER planting is a bit troublesome, but it’s possible. Try to dig up some of the soil near the plant but don’t damage the roots. This might help the plants recover, but there is no guarantee.
4. A Nutrient Deficiency
A deficiency of any major nutrients or vitamins needed for growth can cause yellowing or other growth problems. The best way to determine this is to perform a soil test; this helps you target the best solution.
The most common reason for tomato leaves turning yellow is a nitrogen deficiency because gardeners typically don’t fertilize tomatoes enough. These plants are heavy feeders; these plants actually require twice the amount of fertilizer that cucumber plants need.
If you don’t provide your tomato plants with enough fertilizer and nitrogen, the older leaves start to turn yellow, and they often fall off the plant.
A nitrogen deficiency always starts with the older leaves because the plant is sending nitrogen to the younger leaves to help them live.
If you have a magnesium deficiency, it produces yellowing that looks like spots or speckles on the older leaves first. One way to target this problem is to spray the leaves with an Epsom salt mixture.
Another reason for tomato leaves turning yellow is an iron deficiency, but an iron deficiency typically shows signs on the youngest leaves first.
That’s an important difference to note!
5. Early Blight
Diseases are a prime reason for tomato leaves turning yellow. Some experts recommend that gardeners spray their plants with fungicides on a regular basis to protect against tomato fungal diseases!
Early blight is a serious problem, and it starts at the bottom of the plant and moves up as the leaves start to die at the bottom of the plant. You’ll notice yellow leaves and small spots or lesions that eventually grow larger. Over time, early blight presents itself with a bulls-eye appearance.
Typically, early blight doesn’t affect the fruits until much later when the disease is severe. When you notice these leaves, cut them off. The longer that the leaves stay on the plant, the more likely it is that the fungus spreads.
Eventually, the plant leaves and stems will turn yellow and brown, shriveling up completely.
6. Late Blight
On the other hand, a fungal disease called late blight is even worse than early blight. It starts on the upper leaves of your tomato plant. You’ll find large, oily-looking lesions on both the leaves and stems, and you might find some fuzzy growth on the underside of the leaves.
Late blight moves rapidly throughout a garden because cool, wet conditions cause the number of spores grows quickly. Even the best fungicides cannot control established lesions caused by late blight.
7. Fusarium Wilt
If your tomato leaves are only yellow on one side of the plant, you might have fusarium wilt. This tomato fungal disease shows up during warm weather, and it starts with the bottom, older leaves first.
Fusarium wilt is hugely problematic, and it causes stunted growth. Chances are your plant won’t produce fruit if it’s infected with this disease, but it often doesn’t appear until fruits appear on your plant. It causes stunted growth, but if you remove the branches fast enough, you might be able to limit the progression.
Unfortunately, fusarium wilt has no cure, so the crops have to be destroyed, and you have to practice crop rotation in the follow years.
8. Septoria Leaf Spot
Another tomato fungal disease that your plants might contract is septoria leaf spot. At first, this disease looks a lot like early blight with spots on the lower older leaves that start yellow but eventually turn brown or grey.
When your plants have septoria leaf spot, the spots are smaller, and the plants will have more spots than early blight. As it gets worse, the spots grow, coalescing and turning into a large, brown area on the leaves. You might notice water-soaked lesions on the underside of the leaves.
When left to grow, septoria leaf spot will cause the leaves to turn yellow, then brown, and then finally die. Removal of the leaves as soon as you notice them on your plants is a must; it helps to prevent the spread throughout the rest of your plant.
9. Powdery Mildew
Most assume that powdery mildew has a whitish-grey powder on the surface, and that’s true. However, it’s most often noticed on the older leaves first as a yellow-spotted appearance. Then, when you closely inspect the plant, you’ll find the powder.
10. Pest Infestation
Tomato plants are known for having pest issues, so when you notice tomato leaves turning yellow, it’s time to check your plant to see if you find any signs of an infestation.
A few of the garden pests that might cause your tomato leaves to turn yellow include:
- Spider Mites
- Flea Beetles
- White Flies
Even if you see tomato leaves turning yellow, try not to panic. Many of the problems can be slowed down by proper tomato pruning, or you might need to add some fertilizers to fix a nutrient deficiency. Make sure you correctly identify the problem before attempting to fix why your tomato leaves are turning yellow.