Yellow Leaves on Tomato Plants: How to Determine the Cause

If you happen to notice yellow leaves on your growing tomato plants, you definitely may have cause for concern. Tomato plants with yellow leaves could be something simple, like just needing more water, or it can also be a very serious disease or fungus. Figuring out the cause of the yellow leaves will let you to know if you can save your plants or if you need to dig them up and sacrifice them.

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Watering Issues

Hopefully your yellow leaves will fall into this category as it is the easiest to take care of. Some tomato leaves may be turning yellow due to lack of water. If this is the case, you will notice that the leaves on the top of the plant are yellowing and wilted. You can simply make sure you are watering the plants enough.

On the other side of this, if you see leaves at the bottom of the main stalk yellowing, it is due to not enough sun and not getting nutrients from water. This usually only happens near the end of the growing cycle when the fruit is almost ripe. You should simply not worry about it at this point because you are almost ready to harvest! It is just a natural part of the cycle.

Soil Chemistry

Another simple reason your tomato plants leaves may be turning yellow is the soil chemistry. Lack of nitrogen can cause yellowing, for instance. You can easily check the soil chemistry with testing strips from any greenhouse or gardening store. Once you add the necessary chemicals, your leaves should perk up.

You may also consider putting some fertilizers on the plants. Natural ones work best. Many people recommend fish heads in the soil around the tomatoes. You can usually get them at your local butcher or if you are a fisherman, use your own! Composting can also help, but it usually takes time for you to make your own natural compost. You may want to start it now to get ready for the next season.

Fungus or Disease

This is where it may get scary. Fungus and diseases can cause yellowing of your tomato leaves and some of them are deadly for plants. One of these diseases is called “alternaria alternate”. It is also known as “blight”. If you notice one or more of your tomato plants have blight, you will need to make a decision as it is almost impossible to treat. You may be better off destroying the affected plants by pulling them up instead of taking the chance that the blight will spread to other plants in your garden. This particular disease can also spread to other types of plants in your garden as well.

Pests

Some insects can come into your garden and these little pests can cause yellow leaves as well. Many of these are worms or caterpillars as well as beetles who may lay eggs on your plants. Usually you can get rid of these with insecticides, but you definitely want to make sure you actually have a pest problem before putting chemicals on the plants.

You can find organic ways to get rid of many pests which will be a healthier way to combat the icky insects that have made your plants their homes.