Plant Cultivation

Why Are My Tomato Leaves Turning Yellow: 5 Reasons to Know

Why Are My Tomato Leaves Turning Yellow

Why Are My Tomato Leaves Turning Yellow & How to Fix

Prized for their delicious fruit and versatile uses, tomatoes are a popular choice for indoor gardening lovers. However, one of the most common issues that tomato growers encounter is yellowing leaves. Why are my tomato leaves turning yellow? This disconcerting sign can signal a variety of problems, some easily fixable and others more complex. No matter what the causes, we’ve got you covered in this post.

Table of Contents

Nutrient Deficiency 

Tomato plants rely heavily on plenty of nutrients to grow healthy foliage and yield tasty fruits, including Nitrogen, Potassium, Magnesium, Calcium, and Iron. Among them, the absence of adequate nitrogen is the top culprit for tomato leaf discoloration. Without nitrogen, the entire older leaves on the down parts typically start to turn yellow, as these leaves divert nutrients to younger, growing leaves. 

tomato leaves turn yellow due to nutrient deficiency

image source: Shutterstock/Mironmax Studio

Additionally, other nutrient deficiencies mentioned above can also cause tomato leaves to turn yellow, but they do present slightly different characteristics on the leaves though. Let’s find out how to distinguish them so you can better remedy the nutrient deficiency. 

  • Potassium deficiency: As an essential nutrient needed for fruit quality and yield, lack of Potassium can cause the outer edges of leaves to go yellow, then turn brown and appear burned. Another symptom is the presence of yellow shoulders on the tomatoes, hampering the fruit's ripening process. 
  • Magnesium deficiency: Leaves turn yellow but veins remain green. You can also find spots or blotches on mature leaves.
tomato leaves turn yellow due to magnesium deficiency

image source: SCOT NELSON/FLICKR

  • Calcium deficiency: Newer leaves may turn yellow. Meanwhile, it may cause blossom end rot, where the bottom of fruits develops brown or black spots.
  • Iron deficiency: Newer leaves become yellow while retaining green veins.

How to Fix Tomato Nutrient Deficiency 

Before adding or getting rid of any fertilizer, doing soil testing is the most reliable method to understand what nutrients your soil needs, as it provides insights into soil composition, pH, and nutrient levels. 

Once you figure out the situation, you can ask for recommendations on which fertilizers to use in local farm shops. You can also refer to the chart below for an average idea about which nutrient to add during the different growth stages of tomato plants. 

Seedling Stage

Vegetative Stage

Flowering Stage

Primary Nutrients

A balanced mix of nitrogen (N), phosphorus (P), and potassium (K)

Higher levels of nitrogen

Lower levels of nitrogen but high levels of phosphorus and potassium

Secondary Nutrients

Calcium and magnesium

Calcium and magnesium

Calcium and magnesium

Tomato Diseases 

Unfortunately, tomatoes are pretty vulnerable to a wide range of dieases, and some of them are the ones to blame for leaf discoloration. According to Tomato Diseases & Disorders by the University of Clemson's College of Agriculture, Forestry, and Life Sciences, the following plant dieases are likely to cause yellowing of the tomato foliage. 

  • Early Blight (Alternaria solani)
  • Late Blight (Phytophthora infestans)
  • Fusarium Wilt (Fusarium oxysporum)
  • Verticillium Wilt (Verticillium albo-atrum, Verticillium dahliae)
  • Septoria Leaf Spot (Septoria lycopersici)
  • Tomato Yellow Leaf Curl Virus
  • Tomato Spotted Wilt Virus
  • Mosaic Virus (Tobacco, Cucumber)

How to Fix Tomato Diseases

Fortunately, although there’s a wide collection of viruses, the report above covers comprehensive guides for each case to help you recover yellowing leaves and solid tips to avoid these diseases. 

Herbicide Drift Damage

When discussing the reasons for tomato leaves curling, we mentioned the damage brought by herbicide drift. Guess what? The herbicide drift is also responsible for tomato plants turning yellow. That’s because this fruit is naturally super sensitive to the chemicals in the herbicide, including Glyphosate, 2,4-D, Atrazine, etc. Even if it’s not your original target for weed-killing, the plant can easily get affected by the drifted herbicide. 


Can I Recover Yellow Leaves from Herbicide Drift

Truth speaking, it’s not likely to bring yellow leaves back to normal once damaged by the herbicide. However, you can take action as soon as possible to stop the contamination and give a few weeks for new leaves. To further limit the weed, it’s suggested to opt for hand weeding and mulching as the replacement for herbicide. 

Excessive Minerals 

Tomatoes grown in pots and containers can easily accumulate too much salt and other minerals in the soil, especially when the water contains a heavy amount of salt. When that happens, it’s hard for tomatoes to absorb water and essential nutrients like nitrogen, phosphorus, and potassium from the soil, making tomato plants turn yellow.

How to Get Rid of Minerals Stuck in the Soil

  1. Flush the Soil

You can water the plant thoroughly, allowing water to run out of the bottom of the pot. This will help flush out excess salts. Make sure to discard the water that drains out to prevent reabsorption of the salts.

  1. Repotting

If the salt build-up is too severe to be flushed out, you might consider repotting the plant into fresh soil. Do remember to rinse the roots gently to remove as much of the old soil as possible.

  1. Check Your Water

It’s possible your water source is high in salts or minerals, especially if you are living in arid or coastal regions. For a situation like this, consider using filtered water to feed your plants.

Overwatering or Underwatering 

Proper watering is the key to thriving tomato growth. Theoretically speaking, tomato plants need at least 1-2 inches of water per week to maintain vitality. The recommended metric can float up and down, depending on the actual soil moisture. If not properly watered, tomato roots will find it hard to take up nutrients due to a lack of oxygen in the soil. Therefore, tomato leaves can get yellow and wilt with brown spots. 

watering tomato plants

How to Fix Yellowing Tomato Leaves from Improper Watering

Before watering the plants, always sink your fingers into the soil to test the moisture level. If the soil is still wet deep down 2 inches, then it’s fine to give it a break without watering. On the contrary, once the soil feels dry, water the plants slowly and thoroughly to allow for a complete trickle into the soil. 


Why are my tomato leaves turning yellow? With a long list of causes explained above, including nutrient deficiencies, tomato dieases, herbicide damage, etc., you can diagnose the specific issue and implement the right solution. Remember, yellow leaves are the plant's way of sending a distress signal; heed it, and you can often reverse the issue before it severely affects your crop.

FAQs about Tomato Leaves Turning Yellow

  • How do you fix yellow leaves on tomato plants?

To fix yellow leaves, you should first identify the cause, which could range from nutrient deficiencies to diseases. Depending on the issue, you may need to adjust watering, add specific nutrients, or treat specific diseases. 

  • Should you remove yellow leaves from tomato plants?

It depends on the cause. If the yellow leaves are diseased, removing them can prevent the spread to healthy leaves. However, if it's just a nutrient issue, fixing the nutrient imbalance would help recover yellow leaves from the plant.  

  • Does overwatering cause tomato leaves to turn yellow?

Yes, overwatering can cause leaves to turn yellow because it creates conditions that make it hard for the plant to absorb nutrients from the soil. Overwatering may also lead to root rot.

  • What are the signs of overwatering tomato plants?

Signs of overwatering include yellow leaves, wilted appearance, and waterlogged soil. If the plant has puffy, swollen stems or leaves that look too full, it may also be a sign of overwatering.


About Ciki

Ciki has been navigating the digital world of SEO for over 4 years, applying her expertise originally in the software sector before turning her attention to indoor gardening. Merging her tech-savvy background with a passion for nature, Ciki offers a unique perspective on gardening, blending modern techniques with time-honored traditions.

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