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7 Causes & Cures of Yellow Leaves on Tomato Plants

From his early days, Brandon helped his grandmother in her garden. He has always been passionate about tomatoes.

(Above: Yellow leaves on tomato plants.) Have you ever wondered, "Why are my tomato leaves turning yellow?" Worry not; this guide will help you understand the yellowing of tomato leaves and provide solutions.

(Above: Yellow leaves on tomato plants.) Have you ever wondered, "Why are my tomato leaves turning yellow?" Worry not; this guide will help you understand the yellowing of tomato leaves and provide solutions.

Why Are My Tomato Leaves Turning Yellow?

There are plenty of reasons for the tomato leaves to turn yellow. Sometimes, it is natural and not a cause of worry, but all the other times, you need to pay attention. Yellowing leaves on tomato plants could indicate something as simple as too much water or something serious (e.g., a pest attack which could turn ugly).

Some of the factors that can turn your tomato leaves yellow include:

  1. under-or-overwatering,
  2. nutrient deficiencies, and/or
  3. pests or possible diseases transmitted through these pests.

Are There Solutions?

Some of these are easy to fix while the rest could be a tad bit tricky to diagnose and treat. In some extreme cases, there is no saving the plant and you're going to have to get rid of it to prevent the problem from spreading across your garden.

If it's your first time growing tomatoes or if you've had problems in the past and issues such as the yellowing of the leaves are not a rare occurrence, I would highly recommend that you read my article on growing tomatoes from seed. This guide also works for you if you buy saplings as it covers the different stages of growth.

Through this article, we're going to be diagnosing the cause of one symptom, but the guide above would help you sort out your plants so that you would not be in the same situation with yet another problem further down the road, blossom end rot during fruiting season, for instance.

Causes of Yellow Tomato Leaves

CauseSolution

Excess or deficient water

Learn how to gauge how much water your plant needs (see below).

Compacted soil

Work to aerate the soil.

Virus, fungus, or bacteria

Read on for a complete list of solutions.

Pests

Below, you'll find the signs of and solutions for an infestation.

Nutrient deficiencies

It could be an imbalance of nitrogen, minerals, alkalinity, etc.... see below for diagnoses and solutions.

Lack of sun

If you can move the plant to get more sun, then do; if most of the plant is unaffected, don't worry about it.

A normal stage of the growth cycle.

Don't worry about it!

What Makes Tomato Leaves Turn Yellow?

1. Overwatering and Fusarium Root Rot

Tomato plants need perfect soil moisture levels. The soil shouldn’t be too wet nor too dry and it is important that the soil is dried out, but not too much before you water again. Determine how much water is needed by taking your weather conditions, the soil type, and the level of mulch you use into account. In some places, you'll need to water multiple times a day, but in others, watering just a few times a week is fine.

Read my guide on watering tomatoes for best techniques and precise quantities (for most gardens) needed for tomato plants which is applicable to most vegetables too.

Root Rot is one of the possible outcomes if you over-water potted tomato plants or if your garden has soil that does not drain well. When the roots of the plant are flooded for extended durations they cannot breathe anymore. This lack of oxygen causes the plant tissue to die and eventually decay. The decayed sections of the root spread and in time results in the death of the plant. In addition to this, there is also the root rot fungus that can be dormant in the soil but is activated by just one instance of overwatering.

Is Your Plant Suffering from Root Rot?

Root rot is one of the problems that are usually observed too late and the plant in most cases cannot be saved. You can be sure that root rot is your culprit if you notice the following:

  • The bottom leaves of the tomato plant have turned yellow indicating fusarium root rot.
  • The stem just above the ground is brown, but not a mature brown (like wood) that may even go higher up the plant, instead it is a brown that is not firm and is very often mushy.
  • If you notice a browning of the stem, you may want to slowly dig around the stem to see an inch or two below the soil. Do this carefully as you do not want to damage the plant (yet). Are you noticing this section is all wet and wrinkled like stale vegetables in the fridge? If yes, that's a clear sign of root rot.

I, fortunately, do not have any pictures to add, but I recommend you look here (a page from Cornell University) to see what this problem could seem like or better still, this image.

Looking at this picture, my first guess would be that this plant is suffering from a Magnesium deficiency.

Looking at this picture, my first guess would be that this plant is suffering from a Magnesium deficiency.

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Read More From Dengarden

Dealing with Root Rot

Unfortunately, your plant cannot be saved and it's going to die, eventually, unless you spotted the problem very early.

The culprit is the root rot fungus if you know for sure that your plant has never been consecutively over watered and that there was never heavy rainfall that resulted in stranded water around the plant.

The fungus is usually dormant and can live in the soil for a few years. As described earlier, it can be activated by just a single session of overwatering. On the contrary, natural root rot will not happen if your tomato plants are flooded just once for a few hours.

In cases where you are not sure of the cause or if you know for a fact that it was caused by the fungus, you're going to have to throw away the plant. Do not put it in a compost pile. Also, throw away all the soil from the container or dig up a decent amount of soil from your garden (where the plant stood) and throw it away.

It would be wise to not use that part of your garden for a year or two or look into local root rot-resistant varieties. Also, clean up the tools you've used to dig up the plant, as the fungus can spread through your tools to the other parts of your garden.

Saving a Plant from Root Rot

If you're growing tomato plants in containers and if you happened to come here after noticing the yellowing of the bottom leaves, but none of the other problems described in this article seem to be the issue, you could have potentially caught root rot at the early stages where the roots have been damaged and are incapable of delivering the demanded amount of nutrients, thus causing the yellowing of the leaves. I suggest that you continue reading on and go through the entire article before you pull up your plant to investigate

Also, for it to be root rot, you would have to have over-watered your plants at least once or you would have to be using soil that was not sterile, to begin with. If these are not conditions you could check off a list, the problem is something else entirely and it is very possible that I have not covered the issue, but it isn't root rot.

Once root rot is confirmed it's best to dig up the plant along with some soil so that the roots are intact and then wash the roots under gentle cold running water to get rid of all the soil. You may notice some of the decayed sections of the root fall off.

After carefully washing, use a shear to chop off any mushy black sections of the roots before washing again. Next place the roots in a gentle fungicide to kill the f