Tomato plants turning purple is a headache for every grower that is caused by several reasons, including nutrient deficiency, high or low soil pH, sunburn, and viral diseases.

Truth Behind Tomato Plants Turning Purple

But luckily, it is not a big problem as different solutions can get rid of purple coloration easily.

Continue reading to know everything about the reasons and how you can solve them.

Why Do Tomato Plants Turn Purple? 

Tomato plants usually become purple when there is a phosphorus, potassium, and magnesium deficiency. In addition, improper lighting, poor soil, pests, and different stress factors, like cold temperatures, storms, etc., also cause the plants to change their color to purple. 

 – Soil Deficient in Phosphorous

Phosphorus is in charge of the plant’s overall growth rate. When the bottom section of the leaf begins to turn purple, this is a common sign of phosphorus deficiency. Furthermore, if the leaves turn dark green, it is also a sign that tomato plants need phosphorus. 

In addition to turning colors to purple, phosphorus deficiency in tomatoes can cause leaf cupping, necrotic leaf patches, and slow growth. It is because photosynthesis does not occur smoothly when plants turn purple. Furthermore, this condition might lead to delayed blooming and maturation as well.

– Soil Deficient in Potassium 

Potassium is a critical nutrient essential for healthy plant growth. It aids in forming sugars and starches, leading to better flowering and fruiting of plants. Potassium shortage can cause plants to grow poorly and change their leaf color to purple.

– Soil Deficient in Magnesium 

Magnesium is another important nutrient that is also an integral component of chlorophyll molecules. When plants cannot absorb this nutrient, the leaves start to turn purplish. Furthermore, you may also see brown tints when plants are magnesium deficient. 

You should take purple and brown tints on plants seriously due to magnesium undersupply. The reason is that this nutrient is crucial because of its link with chlorophyll. We all know that chlorophyll is necessary to carry out the process of photosynthesis.

When leaves turn purple because of magnesium insufficiency, it means there is also chlorophyll deficiency. This results in stunted and poor plant growth with poor fruiting.

So, how to know which soil is deficient in which nutrient? Well, for this, you will have to do soil tests. You can either collect soil samples and send them to the lab for testing or purchase soil testing kits and test yourself.

– Test the Soil PH

Plants need soil of a specific pH range for proper growth. If the pH is not optimal, they won’t be able to take up nutrients, leading to nutrient deficiency. As a result, plants show abnormal growth, including purple leaves.

According to the USDA, tomato-fruiting plants prefer slightly acidic soil. This means that the pH of the soil should be between 6.2 and 6.8 for these plants. If the pH is above or below this range, there is a higher possibility of nutrient deficiency, which will turn leaves purple-ish. To confirm whether pH is the main reason, you can use any pH meter and find out the present acidity or alkalinity of the soil.

– Plants Being Burnt by the Sun

When exposed to intense light (artificial light or sunlight), many plants, including tomato seedlings, produce anthocyanins to protect themselves. This turns their leaves and even stems purple. Tomato stems turning purplish is a big problem as nutrient and water uptake are also affected. 

If you are growing tomatoes indoors, be careful about the lighting. Plants turning purplish under grow lights are not ideal if you are looking for better growth and high-quality fruiting. So, if you observe purple coloration, one of the first things to do is check how much light plants receive and at what intensity. 

– Infection by Virus

Another major reason for purple tomato leaves is viral diseases. The most common disease is the tomato leaf curl virus, which is a viral infection caused by whiteflies. Plants affected by this first have cupped or pale green leaves. Then, the underside of the leaves starts to have purple veins. The purplish coloration can then be easily seen on the whole leaf.

Reason for Tomato Plants Turning Purple

If you observe tomato leaves turning purplish and curling upwards, they might also have curly top virus. It is spread by beet leafhoppers, which migrate from the south. Plants infected with this virus can also have yellow patches and usually cease to grow when the disease gets severe. 

Another virus responsible for tomato purple leaves is tomato spotted wilt virus. It is a big headache for growers, spread via thrips. Initially, the plants will have dark brown to purple spots on tomato leaves. Then, with time, the yellow ring marks became visible on the tomato fruits.

– Too Cold Soil

Tomatoes’ younger plants may change their color to purple if grown in low-temperature soil – less than 50 degrees Fahrenheit. The reason is that plants find it difficult to absorb nutrients from soils that are at a low temperature. So, nutrient deficiency arises, which turns leaves purple. 

– Insect Attack

Insects are one of the top enemies of plants. When you grow tomatoes, you are most likely to see psyllids. These are little flying insects that feed on sap. They are easy to identify because they are usually in vast numbers. They inject a toxin into the plants, which leads to color change.

A mild yellowing and purple darkening of the upper leaves is one of the first signs of a psyllid infestation. Lower leaves will also curve slightly upward. In severe infestations, the entire top of the plant will start turning yellow to reddish-purple. So, take tomato leaves turning purple and yellow as a sign of a psyllid attack.

Garden springtail insects can also trouble you when you grow tomato seedlings. Their attack also causes plants to appear purple (but only if the infestation is too severe). In addition, thrips and hoppers also lead to plants turning purplish color.

– Different Stress Factors

If plants are under any stress, the leaves and stems may change their color to purple. The biggest stress is when you try to grow this plant in an unnatural habitat that does not suit it. This condition is often referred to as tomato Purple Leaf disorder. In addition to it, other stress factors can also lead to this problem.

A tomato plant can be stressed by cold temperatures, high heat, lack of watering, physical damage, and sudden weather changes. But the good news is that plants can return to normal when the stress ends. So, how to fix purple leaves and stems? Continue reading to know.

How Do You Fix Tomato Plants That Are Turning Purple?

To stop your tomato plant from turning purplish, add nutrients first. Make sure you apply proper doses of phosphorus, potassium, and magnesium. It is also critical to balance soil pH, provide shade, and fix the stress factors. Furthermore, warming the soil is another effective strategy against plant discoloration. 

– Add Phosphorus

The quickest solution to cover potassium inadequacy is to add a phosphorus-rich fertilizer. Such fertilizers are easily available at any gardening or online store. However, some gardeners prefer to use something other than them as they are both expensive and inorganic.

If you don’t want to add chemical fertilizers and want to treat the problem naturally, then go for rock phosphate, bone meal, and even eggshells. These products are rich in phosphorus and other minerals that can improve the soil’s nutrient profile. You can also top the soil with organic mulch to make it better.

– Add Potassium

Just like in the case of phosphorus, give tomato seedlings/plants a potassium-rich fertilizer when they are potassium deficient. You can also choose fertilizers like potassium sulfate, tomato feed, wood ash, or organic potassium supplies generated from sugar beet processing to control the deficiency.

In addition, you can also go for seaweed or kelp-based fertilizers, which are also a great source of potassium and can enrich the soil with this nutrient. You can also try granite dust to provide doses of potassium.

– Add Magnesium

For magnesium-deficient plants, you can use magnesium sulfate, generally known as epsom salts. Add one tablespoon of this salt to a half-gallon of water and carefully mix it. Spray the solution on the plants’ leaves every two weeks, and they should be back to normal.

Solution for Tomato Plants Turning Purple

Organic compost is also a rich source of magnesium. You can add it to the soil or mix it to provide this nutrient. Also, ensure you don’t add any calcium-rich fertilizer when plants are magnesium deficient, as doing this can only worsen the matter. Calcium gets in the way of magnesium absorption, and the deficiency can get bad.

– Adjust the Soil PH

It would help if you did soil tests periodically to stay updated on soil conditions. You can get a pH meter easily, which will accurately measure the soil’s current pH. If the reading is not what you expect, adjust the pH as soon as possible.

Suppose the pH of your soil is too low (acidic); you can bring it back to normal by adding lime (calcium carbonate) or dolomite lime (calcium magnesium carbonate). If the pH of your soil is high (basic or alkaline), you can apply sulfur to decrease it.

– Protection From Sunburn

If tomatoes are exposed to direct sunlight for long periods, consider using row covers. These protect tomato leaf burn, allowing only 50 percent to 95 percent of light to get through. Furthermore, row covers also shield plants from cold and parasites.

You can also use shade cloth. The amount of shade provided by shade cloths varies differently. Some let only 5 percent of the light pass through (strong shade), while others allow 95 percent of the light. You can also try re-locating tomato plant pots to different locations where optimal sunlight falls.

– Viral Diseases Solution

Unfortunately, there are no 100 percent effective treatments for the curly top virus. However, you can take steps to prevent other plants from having a viral infection. You should apply neem oil spray to sway all the harmful insects. 

If you notice any psyllids, dusting the leaves of your plants with sulfur might be helpful. Make sure you apply the underside of a tomato leaf, as psyllid nymphs reside there. If you spot any other insect, applying chemical insecticides is a good option to control the infestation.

Also, removing infected plants from the garden is a good option to prevent the virus from spreading. You should also not use the discarded plants as compost anywhere else as this can also lead to virus spread. Furthermore, growing insect-resistant tomato varieties is another great way of managing insect attacks.

– Warm Up Soil

To avoid cold soil problems, you should plant tomato seedlings later in the season when the soil is considerably warmer. These seedlings are unlikely to survive temperatures below 50 degrees Fahrenheit. The ideal soil temperature is between 65 degrees Fahrenheit and 85 degrees Fahrenheit.

Controlling the temperature is relatively easier if you grow seedlings in a greenhouse or cold frame. There, growers usually use heaters, heat mats, or hotbeds to change the temperature to the optimum.

– Plant Stress Fixing Measures

It is critical tomato plants face no stress if you want top-quality fruits. You should water one to two inches of soil weekly for proper growth. If you are growing outdoors and feel that a storm is coming, you should bring the weaker plants and seedlings inside your home. 

Also, ensure you place the plants where they receive sufficient light (not more, not less). If you are growing instead, put them at an ideal distance from grow lights. Covering the plants in the afternoons to protect them from severe heat is another good practice you can follow. If the weather is hot, grow plants in a greenhouse or inside. These measures will prevent them from being under stress.

Causes and Solutions for Purple Tomato


You now know tomato plants turning purplish is not a big problem, and it is easy to deal with this situation. Let’s sum up the key points discussed above so that you don’t miss out on anything:

  • You must apply phosphorus, potassium, and magnesium-rich fertilizers, as nutrient deficiency is the leading cause of purple tomato stems and leaves.
  • Spray neem oil to protect your plants from insects and viral diseases.
  • To avoid stress, water plants appropriately, grow the seedlings a bit late for warmer soil, and place pots at an ideal location where they receive sufficient sunlight.

So, follow these points and never face the problem of plants turning purple again!

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