6 Reasons Why Your Tomato Leaves Are Turning Purple (Easily Fixed)

When you look out at your tomato plants and see their leaves starting to turn purple, it can be alarming. Don’t worry, though – there are usually several reasons why this happens, and most of them are easy to fix.

Here are six of the most common causes of purple tomato leaves, as well as how to correct them:

1. Potassium deficiency

The effect of potassium on photosynthesis is well documented. It’s also true that potassium plays an important role in encouraging photosynthesis.

This is particularly true for plants that are young or are having difficulty absorbing enough potassium to sustain normal growth.

For these plants, a good dose of potassium could help improve their health and coloration.

As the climate warms, leaves might turn to their natural green color. But this could have an adverse effect on fruits if they don’t have sufficient nutrients to support a normal yield of fruit.


To address the potassium deficiency in tomato plants, you should feed them with fertilizer that is high in potassium.

The best sources of potassium include potassium sulfate, potassium nitrate and potassium chloride.

2. Magnesium Deficiency

Magnesium is an important mineral for plant growth and development. In fact, it’s found in the central core of the chlorophyll molecules that are responsible for plant photosynthesis.

Without magnesium, there is a lack of chlorophyll, which results in stunted and poor plant growth and leaves that can take on a darker or purple appearance.

Organic compost is a good source of magnesium. It’s easy to add by adding organic compost regularly to the soil, mixed in or as a mulch. 

You can also add magnesium in the form of magnesium sulfate, known as Epsom salts


Epsom Salt has been recommended for plant fertilization as 1 tsp per quart. Drop the solution on the leaves of the plants every 2-3 weeks and they should return to their normal appearance.

3. Cold Soil

Tomato seedlings often face problems of low nutrient absorption as the temperatures of their growing soil is kept low. As temperatures go up, the plant absorbs more of the nutrients available in the soil.

If you don’t know the correct planting time for your type of seed then it is best to get professional help. Otherwise, the plant may be stunted or deformed due to a too early or too late planting.


To prevent this, it is best to make sure that the soil is warm enough to plant seeds at the right time.

4. Phosphorous deficiency

Tomato plants require high levels of phosphorous in order to grow. However, plants grown in cool, wet conditions will struggle to absorb phosphorous, which causes them to turn purple. This is due to low levels of available potassium.

Phosphorus is an important nutrient in tomato plants as it plays an essential role in building healthy cell walls and is used as part of the process of photosynthesis, which is the process through which plants generate food by converting carbon dioxide and water into sugars.


If the issue continues, you’ll want to feed the soil around the plants with superphosphate or bone meal and top with an organic mulch to warm the soil.

5. Sunburn

Sunburn, in the botanical sense, is a symptom of over-exposure to high intensity light.

The red or purple leaves that you see on tomato plants are the result of a chemical reaction between chlorophyll and sunlight.

In this reaction, called photosynthesis, green chlorophyll turns into red or purple chlorophyll.

This can be due to seedlings getting too close to the light or just getting too much light in general.


Adjust the light to where you can see everything but can also provide sufficient lighting for photosynthesis.

Use the right fertilizer at the right time – check instructions. And watch out for that sun! It’s one of the biggest dangers.

6. Viral Infections

Some viruses will cause tomatoes to develop purple spots and rings. Thrips transmit the tomato spotted wilt virus (TSWV) which can cause the leaves to turn yellow and distort and form dark brown to purple spots.

Thrips are tiny insects that live off the organic material found in decaying plant matter.

They are hard to spot but if you see them on plants, spray them with insecticidal soap and keep the area well watered.

You may want to also apply neem oil. Thrips can spread viruses.


Use row covers to protect tomato plants. In case of Tomato Spotted Wilt, you need to prune and destroy the infected plant and don’t spray the infected plants with any pesticides.

How to Prevent Tomato Leaves from Turning Purple

Planting tomatoes in containers can help reduce the risk of some pests and diseases. However, growing tomatoes in containers is not a good idea in every case.

You may want to consider alternatives such as growing your tomatoes in your garden if there is space or purchasing them from a local farmer’s market.

In the natural environment, potassium can be removed more easily from lighter soils or sandy soil. In contrast, potassium is held in clay soil due to its strong bonding with other components such as clay minerals.

Frequently Asked Questions:

Q: Why are my tomato fruits purple?

Phosphorous deficiency is one of the main causes of a plant’s leaves turning purple. The discoloration may extend from the center of the plant and become more noticeable near the bottom.

Phosphorous deficiency is most prevalent during winter and spring.

Q: How long does it take for the tomatoes to turn purple?

It takes a couple of days for the color to develop.

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