June is a big month for tomatoes. Right now they should be putting out tons of new branches and leaves, their stems should be thickening, and the first flowers and fruit should appear soon. But if your tomato leaves are turning yellow this early in the season, then it’s crucial to figure out the cause and treat the problem fast.
Yellow leaves on tomatoes can occur for a variety of reasons. Some of them are no big deal and easy to fix. But if others are left untreated, they could have serious implications on your plants for the rest of the season. Your harvest could be much smaller or even nonexistent, depending on the severity of the problem.
Whatever the issue, though, there is a solution. But the first step is identifying the problem. I’ll walk you through the three most common causes of yellow tomato leaves in June and how to deal with each of these complications.
1. Nutrient Deficiencies
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The most likely cause for yellow leaves on tomatoes in June is a nutrient deficiency. Tomato seedlings often turn yellow before you even transplant them into the garden because they’ve used up all the nutrients built into the seeds from which they sprouted. That’s why it’s important to fertilize tomatoes in Juneespecially if you didn’t give them a dose of fertilizer when you transplanted them into the garden.
Often leaves turn yellow when there is a nitrogen deficiency in the soil – nitrogen is what stimulates lots of green, leafy growth. But phosphorus and potassium are also key for producing lots of fruit, so you don’t want to overdo it with the nitrogen in order to get green leaves at the expense of actual tomatoes. Though, a potassium deficiency can cause yellowing around the edges of your tomato leaves as well.
Iron and magnesium deficiencies can also cause yellowing leaves on tomatoes. But rather than the entire leaf turning yellow, these nutrition problems exhibit themselves in different ways. Iron chlorosis causes the leaves to yellow and the stems to remain green. A magnesium deficiency causes leaves to take on a yellow, splotchy appearance.
The best course of action is to first do a soil test – this quick and easy at-home soil test kit from Home Depot is a great option for immediate results – before choosing a fertilizer for your plants. A one-size-fits-all fertilizer is not ideal, especially if your plants are already turning yellow. A simple soil test will tell you exactly what nutrients your tomatoes are lacking and guide you to choose the proper plant food for your particular plants.
2. Diseases
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A variety of different tomato diseases can cause leaves to turn yellow. In June, the most likely diseases to impact your plants are:
- Early Blight
- Late Blight
- Septoria Leaf Spot
- Leaf Mold
- Bacterial Spot
- Fusarium Wilt
- Tomato Pith Necrosis
- Tomato Yellow Leaf Curl Virus
The best way to both prevent these diseases is to provide proper tomato care. Do a soil test before planting and amend your soil based on those results. Water plants at the base to prevent splashback onto leaves, which can spread diseases. Provide consistent irrigation so plants are not stressed and more vulnerable to disease. When pruning tomato plantsalways clean your pruners between each plant to prevent disease spread.
As an extra precaution, especially if you’ve encountered any of these diseases in previous years, choose disease-resistant tomato varieties to grow in your garden. Botanical Interests is a great source for disease-resistant tomato seeds. Or you can shop disease-resistant tomato starter plants from Bonnie Plants.
3. Herbicide Drift
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Another cause of yellow leaves on tomato plants is herbicide drifthowever, this is much less common. Still herbicides can travel via the wind for up to a mile and harm your tomato plants, causing them to twist, turn yellow, and become stunted. This issue is more likely if you live near a commercial farm, but it can still occur in any neighborhood.
If you use herbicides in your landscape, never apply them on a windy day and try to stay as far away from your tomatoes as possible. Ideally, you should hand-pull weeds with a tool like Grampa’s Weeder from Walmartwhich works wonders on the dandelions in my yard. You can also try a safer organic weed control method instead, so you don’t accidentally harm your own plants.
Herbicides are also sometimes present in low-quality soil mixes, composts, and mulches. That’s why you should sometimes be careful when using free mulch, free compostor free garden soil. If possible, find out the source of the material to ensure it does not contain unwanted herbicides that can ruin your garden.
