Under typical circumstances, most varieties of tomatoes have green leaves and red ripe fruits, except for Indigo Rose which has unique purple foliage and fruits. It is not common for tomatoes to turn purple under regular conditions.
So when the leaves of the tomato plants turn purple at some stage of their development, you have every reason to be concerned.
Why are my tomato plants turning purple? When tomato plants turn purple it’s a sign of tomato purple leaf disorder or nutritional deficiency. Most likely the soil lacks either potassium or phosphorus or both. Pests, viral infections, too much light, stress, and inadequate soil pH could also cause this leaf disorder in tomato plants.
With so many causes of purple tomato leaves, it’s not always easy to fix the problem before it’s too late. Read more to find out what causes tomato plants to turn purple and what you can do about it.
Tomato Plants Turning Purple – 8 Possible Causes
When tomato plants turn purple, it’s a serious sign. In many cases, the plants will wither and die unless you intervene. You’ll need to find out what’s causing the disorder and remedy the situation before you lose your tomato crops for the year.
1. Tomato Purple Leaf Disorder
Tomato purple leaf disorder is caused by a virus and has the same symptoms as nutritional deficiency and many people don’t take it seriously.
The first signs appear about 6 weeks after transplanting the tomato seedlings. The upper surface of the leaves turns purple but the veins keep their natural color. Then the purplish hue spreads to the rest of the plant. The disease often appears in parts of the plant exposed to sunlight.
There’s no treatment against the virus that causes tomato purple leaf disorder yet. In fact, there’s still a lot that we don’t know about the virus or how it transmits to the tomato fields.
The best way to fix the problem is to pull out the infected plants before they spread the virus to the rest of the tomato plants.
2. Phosphorus Deficiency
When the soil lacks phosphorus or for some reason, the tomato plants can’t absorb the nutrient in the soil, the leaves will either turn purple or dark green.
The soil has to be cool and wet for the tomato roots to absorb phosphorus.
Unlike tomato purple leaf disorder, the purple color associated with phosphorus deficiency spreads across the surface of the leaves as well as the veins, starting from the bottom leaves all the way up.
To fix phosphorus deficiency that causes purple leaves in tomato plants, apply a phosphorus-high fertilizer with a fast-release property (this liquid version produces fast results).
Organic compost and homemade fertilizers are slow-release and take time before the phosphorus is accessible to the tomato plants. Make sure the soil is both cool and moist. Water regularly, and use mulch to improve water retention.
3. Potassium Deficiency
Unlike phosphorus, potassium is only accessible to the tomato roots in warm soil. It’s one of the paradoxes of growing tomatoes — the plants need both cool and warm soil to absorb the necessary nutrients.
Potassium deficiency causes the leaves of tomato plants to turn either purple or yellow. It also causes stunted growth even if the leaves turn green when the soil warms up.
To solve the problem of potassium deficiency, feed the tomatoes with potassium-high fertilizers (again, I recommend this liquid feed). Start the tomatoes indoors until the weather warms up and the soil is no longer cold. Then transplant the tomatoes into the garden.
4. Intense Light
Direct sun exposure works in tandem with tomato purple leaf disorder to cause the leaves to turn purple.
You’ll often notice that the parts of the leaves and fruits exposed to the intense sunlight will turn purple while those in the shade keep their green color, but intense sunlight also causes leaf burn, which gives the leaves and stems a purplish hue.
If the spring turns quickly into summer and the tomatoes get direct sun exposure for long hours, consider using row covers (find them here) to protect the tomato plants against leaf burn.
5. Viruses & Disease
One of the most common viral infections that cause tomato plants to turn purple is the tomato yellow leaf curl virus.
It’s transmitted by whiteflies and causes the veins and the underside of the leaves to turn purple. The upper side of the leaves is usually yellow. The plants become stunted with fewer flowers and poor harvest.
The curly top virus is another virus that causes the top leaves to curl and turn purple. It’s often carried by beet leafhoppers and causes the stems and leaves of the plant to become stiff.
Another disease, tomato spotted wilt, also gives the leaves a purple tint. The virus is transmitted by western flower thrips.
The most obvious solution against all of these viral diseases is to prevent the bugs that carry them from reaching the tomato plants.
Row covers are an excellent option to protect tomato plants against pests and infestations. Remove all infected plants as soon as you discover them and dispose of them safely.
6. Soil pH
Tomatoes, much like many other plants in the garden, prefer slightly acidic soil. As long as you keep the soil pH between 5.5 and 7.5, the tomatoes will not have problems.
The slightly acidic soil is also crucial for absorbing phosphorus through the roots. So when the leaves of the tomato plants turn purple, check that the soil pH is not too high. Alkaline soil prevents the roots from absorbing phosphorus, which causes purple leaves.
Test the soil pH, and if it’s too high (above 8), amend the soil with sulfur or aluminum sulfate. Sulfuric acid is also a good treatment.
Follow the instructions on the packages, and test the soil pH after each application. When the reading goes down to 6 or 5.5, stop adding sulfur.
As I mentioned above, pests can carry viruses that cause different diseases that turn the tomato plants purple. Whiteflies, beet leafhoppers, and western flower thrips are some of the most deadly carriers.
However, other pests feed on tomato seedlings and cause damage to them.
One of the main culprits is garden springtails. They are tiny purple bugs that have small tails that they use to propel them into the air. They make holes in the leaves and stems of the tomato seedlings.
Spray the tomato seedlings with neem oil (I use this organic neem oil routinely), or use a garden hose to flush the garden springtails off the seedlings.
8. Plant Stress
Tomatoes get stressed easily if the environment or growing conditions are not optimal. Cold weather, cold soil, extreme heat, irregular watering, and unpredictable weather changes can stress out tomato plants.
The leaves will change color and wither if the cause of stress persists. The plants will have stunted growth that will affect the yield.
Make sure that the tomato plants are watered regularly. Protect the plants against extreme heat by covering them in the afternoons. If the weather is unpredictable, consider growing the tomato plants in a greenhouse or indoors.
How To Keep Tomato Plants Healthy
To ensure that your tomatoes are growing successfully, start them indoors, and transplant them to the garden after the last frost and when the soil is workable.
To prevent pest infestations, use row covers, or plant the tomatoes in containers. Water the plants regularly, and apply phosphorus and potassium-high fertilizers. Use mulch to keep the soil moist and cool.
Tips for Growing Tomatoes
- Plant the tomato varieties most suited for your microclimate.
- Choose cultivars that are disease resistant.
- Plant the tomatoes in a spot that gets 6 hours of sunlight.
- Protect them against extreme heat in the afternoon with makeshift covers.
- Water the tomatoes regularly as they’re sensitive to drought.
- Use mulch to improve water retention and keep the soil cool.
- Use loamy soil, and amend it with plenty of organic matter.
- Ensure that the soil pH is between 5.5 and 7.5.
- Keep at least 2 feet of space between the plants to improve ventilation and prevent fungal infections.
Thinking about natural fertilizing? Did you consider using milk for plant health?
Why Are My Tomato Plants Not Growing?
Tomato plants need regular watering. Drought causes stunted growth as does cold soil, freezing temperatures, or poor nutrients in the soil. Pests and diseases could also stunt the growth of the plants.
Why Are My Tomatoes Rotting on the Bottom?
Blossom end rot is a common disease that causes tomato plants to rot at the bottom. It’s often caused by calcium deficiency. Apply calcium-rich plant food supplements, and water the plants regularly.
Tomato plants turning purple is a serious symptom that could stunt the growth of the plants or even lead to their death. The causes could be tomato purple leaf disorder, phosphorus or potassium deficiency, viral infections, high pH levels in the soil, plant stress, or all of the above.
Ensure that the tomatoes have ideal growing conditions, water them regularly, and apply a fast-release fertilizer.