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Tomato Leaves Turning Purple – Causes & How To Fix It!

Tomatoes are a rewarding crop to grow. Their plants make a beautiful addition to your garden, and the fruits are delicious when harvested fresh. Caring for your tomatoes, like most plants, requires a lot of work and knowing what dangers to watch out for. When your tomato leaves start turning purple it can be concerning. If your leaves aren’t green does it mean something is wrong? Why would a tomatoes leaves start turning purple?

Tomato leaves or stems turning purple is the result of environmental stressors. Too little fertilizer, lack of nutrients, excessive exposure to grow lights, phosphorus deficiency and cold temperatures can all cause this phenomenon to happen. 

It can be nerve-wracking to see the leaves on your tomato plants turning purple. If you notice this happening to your tomato plants, don’t panic because there is a way to fix the situation. Read on to learn more about what causes tomato leaves to turn purple, how you can fix it, and how you can prevent it from happening in the first place.

Tomato leaves turning purple

Why Are My Tomato Leaves Turning Purple?

Most gardeners are dedicated to giving their plants the best care possible, and it can be upsetting when you see something unusual. Watching the leaves or stems on your tomato plant turn purple is a cause for concern, but it is a fixable situation.

Leaves or stems turning purple on your tomato plants result from environmental stressors. Here’s a breakdown of the different stressors that can cause this phenomenon.

Cold Temperatures

One factor that can contribute to purple leaves is cold soil temperatures. Tomatoes are warm-weather plants, and they need soil temperatures to stay consistently at or above 60 degrees F to grow and thrive.

If the soil temperatures drop below that, it can cause your tomato plants to stop growing and prevent the fruits from ripening. In young tomato plants, you’ll see the effects of cold soil temperatures quickly as the leaves on your plant begin to curl up and turn purple. 

Nutrient Deficiency

Another stressor that can cause your tomato leaves to turn purple is a nutrient deficiency. Tomatoes are sensitive plants, and they need fertilizer that’s rich in phosphorous and magnesium to grow and produce large, healthy fruits. If your plant can’t absorb enough of these nutrients, you’ll see a lack of growth.

The bottom leaves of your tomato plants will start turning purple if they’re struggling to absorb the nutrients they need.

Over-watering

Over-watering can also make it harder for your tomato plants to absorb the nutrients they need, resulting in purplish leaves or stems. Your tomato plants need 1-2 inches per week if they’re planted in a garden. Tomatoes planted in containers may need slightly more water than that, but not much.

It’s easy to over-water this plant, and purple leaves are a sure sign that they struggle to get the nutrients they need. You may also notice small bumps or blisters on the bottom leaves of your tomato plant if over-watering is the culprit for their purple leaves.

Grow Lights

Grow lights are an excellent resource for growing your tomato seedlings indoors before transplanting them outside. You could use them for your plant’s entire life if you’re keeping them in a greenhouse, but these are powerful lights that can cause your plants to harm if you’re not careful.

Tomato plants need around 9 hours of direct sunlight every day to thrive. If you’re using grow lights, then this can be easy to accomplish, but you need to find the right grow lights for your plant.

Tomato seedlings will do best with grow lights that are on the blue-green spectrum or labeled as a balanced light spectrum. Other grow lights will focus on delivering more of the red light spectrum, which can cause your plant to develop a type of sunburn. This can result in their leaves drying up or the stems and leaves of seedlings turning purple.

You should also check the brightness of the grow lights you plan to use. Plants like tomatoes will do best with lights around 7000 lumens. Lights more powerful than this can also cause sunburn, resulting in purple leaves and other symptoms.

Tomato plants can also develop sunburn in your garden, but it’s much less likely. Tomatoes need 9 hours of sunlight to thrive, and if you’re in an area where they’re getting much more than that, you can always shade your plants for part of the day.

Tomato seedling leaves turning purple

How Do You Fix Purple Tomato Leaves?

It can be worrying to see this phenomenon on the plants you’ve put so much time and effort into. Thankfully, you can take steps to help your tomato plant heal from whatever’s causing its leaves to turn purple.

The first step is to identify what’s causing the purple leaves. Since several environmental stressors can cause purple leaves, it’s difficult to nail down exactly what went wrong. Here’s a quick guide that can help you diagnose why your tomato leaves are turning purple.

  • Purple Bottom Leaves and/or stems- This is most likely the result of a nutritional deficiency. Your plants are either over-watered or under-fertilized.
  • Curled-up Purple Leaves- This could result from over-watering or a nutritional deficiency. It could also be due to cold temperatures.
  • Top Purple Leaves- Sunburn is the most likely cause for the top leaves of your tomato plant turning purple. 

Once you understand what’s causing the leaves on your tomato plants to turn purple, it’s time to work on a solution. The solution is going to be about fixing whatever caused the issue.

Nutrient Deficiency

Purple leaves caused by a nutritional deficiency can happen in two ways. Either you’re over-watering your plant, or they aren’t absorbing enough nutrients through the soil, in which case you need to add some fertilizer.

If your problem is over-watering, then that’s an easy fix. Garden tomatoes only need a couple of inches of water per week. You may have experienced an unexpected week of heavy rains, in which case some dry days should fix the problem. You can always create a shelter or overhang to protect your plants from over-watering in the garden.

Tomatoes grown in containers need 1 inch of water per square meter each week. You can calculate the amount of water your tomato plants need based on the size of the container you’re growing them in.

A general rule of thumb for tomato plants is that they need moist soil, so it shouldn’t be too damp or too dry. You can test the soil by sticking your finger down about two inches. If it’s too damp, then you’ve been overwatering your plant. If it’s very dry, then your plant needs more water.

If over-watering isn’t creating a nutritional deficiency, you may not be giving your tomato plants enough fertilizer. Make sure that you’re using a fertilizer that’s rich in magnesium, phosphorus, nitrogen, calcium, and potassium. 

You should first add fertilizer two weeks after planting your tomatoes and then add 1 or 2 tablespoons per tomato plant once every two weeks. Following these guidelines will ensure that your soil stays rich in the nutrients your tomato plants need to grow and thrive.

Cold Temperatures

Tomatoes are warm-weather plants, so getting the temperature just right is essential. The best soil temperature range for tomato plants to thrive is 65-85 degrees F. Tomatoes can begin to germinate in even colder temperatures, down to 50 degrees F, but this can stunt their growth and cause their first little leaves to develop a purple hue.

There are plenty of ways to control the soil temperature for your tomato plants. If you’re using grow lights, that will help keep your tomato plants warm. You could also look into getting a seedling heat map for your tomato plants. 

Grow Lights

Tomato leaves turning purple is a phenomenon that several environmental factors can cause, and if you’ve already ensured that your plant is getting proper nutrition and water, then your grow lights could be the problem.

Grow lights are a great resource for helping your plants germinate inside. However, if they’re too powerful or too close to your plants, then they can cause sunburn to your plants. Sunburned plants often have leaves that are discolored and curling.

To avoid this happening to your tomato plants, make sure your grow lights are on the blue-green or balanced light spectrum. Check that they’re set about 12 to 18 inches away from your plant. You may need to move your grow lights farther away as they grow, or else the top leaves may reach too close to your grow lights and become burnt.

Final Thoughts 

Watching your tomato leaves turn purple can be worrying and is a sign that your tomato plants are under stress. That stress could be from over-watering, lack of vital nutrients, cold temperatures, or even sunburn! It is possible to correct the situation, and this guide will help you determine what’s causing this phenomenon and how to fix it.