5 Signs of Over-Fertilizing Tomato Plants - Backyard Boss
We are reader supported. External links may earn us a commission.

5 Signs of Over-Fertilizing Tomato Plants

Fertilizing is a crucial step in ensuring tomato plant growth and delicious plump fruits. Unfortunately, there is a fine line between too little, the right amount, and too much. And if you lean on one  the side too much, you risk damaging your plants. If you add too little, your yield may be on the weaker side of things as the plant will lack nutrients.

So, how can you tell if you’ve over-fertilized your tomato plants? And what can you do to avoid making a detrimental mistake? Below, you’ll discover the common signs of over-fertilizing tomato plants. After, you’ll learn some of the best tips and tricks to ensure you find the Goldilocks of fertilizing!

Signs of Over-Fertilizing Tomato Plants

Yellowing and Dropping Leaves

The leaves are turning yellow on the tomatoes
Image credits: PrysMichael via Shutterstock

One of the most common signs of over-fertilizing is yellow and dropping leaves. They typically mean something is wrong, so it’s important to inspect your plant immediately. Unfortunately, yellow leaves can also be a sign of poor watering techniques, a lack of nutrients, and even pests and diseases.

The best way to tell if over-fertilizing is the issue is to determine if the plant has any other symptoms listed below. If the plant is otherwise healthy and the soil isn’t too wet or dry, the issue may be fertilizing!

Browning Leaf Tips

Tomato plant with browning leaf tips
Image credits: Davor Denkovski via Unsplash

Browning leaf tips tend to go hand in hand with yellowing leaves, so there’s a good chance you’ll notice both on your plants if they are over-fertilized. 

If you notice brown spots on the leaves, your plant may suffer from an illness such as early or late blight, septoria leaf spot, bacterial spot, or tomato spotted wilt, so watch out for other signs of disease

Heat damage can also cause black or brown leaves, whether in the form of spots or crispy edges, though it’s usually most noticeable on upper foliage.

If you’ve ruled out disease and heat damage, browning leaf tips and margins generally mean that the plant no longer can absorb nutrients. This is because the salt content in the fertilizer burnt the root system.

White Material on Soil Surface

Female hand with fertilizer for plant over soil background
Image credits: Africa Studio via Shutterstock

Over-fertilizing can cause a build-up of salt and nutrients in the form of a crust on the soil surface. It can interfere with plant growth and its ability to absorb water and nutrients. You can reduce these white crystallized coatings by rinsing the plants every four to six months with fresh water.

Overwatering can cause mold on the top layer of soil, so be sure that’s not what your plant is facing. Also, don’t mistake salt build-up for fertilizer pellets!

Slow, Stunted Growth

Watering newly planted tomatoes and potted basil growing in a container garden
Image credits: WNstock via Shutterstock

If you’ve noticed that your plant isn’t continuing to grow or produce fruit, there are several potential issues. Improper growing or watering conditions and lack of care can all result in stunted growth. But if you’ve been doing everything right, the problem may be that you are too heavy-handed with the fertilizer!

Root Rot

Man hand holding plant of tomato with roots in soil
Image credits: Phoenixns via Shutterstock

Root rot can result from overwatering, but it’s also a sign of over-fertilizing. If this is the case, there’s a good chance you’ll notice many of the other conditions, such as yellowing leaves, brown tips, and stunted growth. To confirm your suspicions, check the root system. 

If there are still some white areas, the plant may be salvageable, but if the roots are brown or black the plant might not be savable. Remove any rotten roots and repot or replant the tomato plant. If they are too damaged, the plant may be too far gone.

How to Avoid Over-Fertilizing

Fertilizing Tomatoes' plants
Image credits: encierro via Shutterstock

With all the signs of over-fertilizing covered, consider how you can prevent the issue. Below, you’ll find the best tips to keep in mind to ensure your plant stays happy and healthy!

  • Fertilize tomato plants a few times throughout the growing season.
  • Use compost first and fertilizer if necessary.
  • Apply only the recommended amount of fertilizer each use.
  • Properly leach and rinse the plants to avoid buildup.
  • Avoid using excessive amounts of slow-release fertilizers.
  • Use well-draining potting media and pots with drainage.
  • Test the pH of the soil before fertilizing. Tomato plants should have a soil pH between 6.2 to 6.8.

Get Growing!

Over-fertilizing your tomato plants can result in declining health and fruit production. You may notice common symptoms such as damaged leaves, fertilizer build-up, and slow growth. Fortunately, there are many tips and tricks to keep in mind to avoid over-fertilizing.

If your plants aren’t suffering from over-fertilizing, consider other ways to improve your harvest. Also, make sure you don’t overwater your plant or it doesn’t face diseases or pests. Fortunately, there are plenty of ways to prevent overwateringillnesses, and plagues!

Have you dealt with over-fertilized tomato plants before? Share your experience in the comments below!