Tomato plant problems: rot, curling leaves & sunburnt tomatoes


I studied horticultural sciences at university and in my free time you can find me in my own patch of land, growing anything with roots. I am particularly passionate about self-sufficiency and seasonal food.

Favourite fruit: quince, cornelian cherry and blueberries
Favourite vegetables: peas, tomatoes and garlic

Damage to tomatoes is not always caused by pathogens. Below you will find details on environmental and physiological disorders that can affect tomato plants and our best tips on how to avoid these tomato plant problems.

Bright spots on tomatoes
Sunburn causes light to translucent spots on tomatoes and leaves [Photo: valerypetr/]

It is not uncommon to find damaged tomatoes on your vines. While the damage can come from tomato pests and pathogens, there are also physiological and environmental disorders that can affect them too. Read on to discover which common physiological damage and deformities can occur during the summer and how they can be prevented.

Tomato leaves curling up

If your tomato plant leaves are curling up, it is usually as a result of incorrect maintenance. If these problems appear at the top of the plant, it is usually due to lack of water. Curling on the lowest leaves, on the other hand, occurs if the side shoots and leaves have been pruned a little too much. Over pruning causes a build-up of nutrients in the remaining lower shoots and the leaves curl. But don’t worry, this will not affect the yield and taste of the tomatoes.

Tip: Lack of water or an aphid infestation can lead to the leaves of young tomato plants curling up and becoming deformed. It is also possible that the plant has contracted a viral disease such as curly top. Viruses are transmitted via sucking insects and cause irreversible growth disorders to the entire plant. If you spot a viral infection, dispose of the entire plant to minimize the risk of it spreading further.

Rolled up tomato plant leaves
Tomato leaves curl upwards when nitrogen fertilisation and heat are too high [Photo: Miyuki Satake/]

Why do tomatoes split?

Most gardeners are familiar with the phenomenon of cracked or split tomatoes, but have you ever wondered why this happens? There are two possible reasons. Either the water supply has been too irregular (for instance in summer when heavy showers are followed by long periods with no rain), or the plant has been pruned or cut back too much. In either case, you will find that the tomato fruit splits. If the plant receives too much water when temperatures are very low, the split can appear in the shape of a ring.

The tendency of tomatoes to split depends on the variety. Outdoor tomatoes accustomed to irregular moisture due to rain and drought will be more split-resistant. The splits do heal and form scars and, although that might ruin the aesthetic a little, the fruit is still safe to eat. It becomes problematic if fungal diseases penetrate the open wound and lead to mould or tomato rot. Infected fruits should be disposed of immediately.

Tomatoes burst open on the bush
Tomatoes tend to burst open if they receive water or rain sporadically [Photo: Raksan36studio/]

Greenback on tomatoes

Yellow or green collar (also known as greenback or green shoulder) can be identified when the tissue around the stem base of a tomato remains hard. That part of the tomato does not change colour during the ripening stage. This is a physiological disease that has a number of possible causes:

  • Overexposure to heat from direct sunlight
  • Over pruning
  • Potassium deficiency
  • Over fertilisation of nitrogen

Once again, the choice of variety plays a big role in this disorder. Beef (also called beefsteak) tomatoes and other darker coloured varieties of tomato, including well-known varieties such as ‘Brandywine’, ‘Black Plum’ or the ‘Black Krim’, are particularly prone to green collar. If the tissue around the stem has hardened, it should be removed before eating, however, the rest of the fruit is still perfectly edible.

Tomatoes with green collar
Certain tomato varieties, especially beefsteak and other dark varieties are more prone to green collar [Photo: Jovana Pantovic/]

Blossom end rot on tomatoes

Blossom-end rot is a dreaded physiological disorder in which the bottom of the tomato turns black, sinks and hardens. The cause is a lack of calcium, and the tissue collapses due to lack of stability. Apply lime when planting, and again as needed between June and August. This will ensure the plant has a sufficient supply of calcium and will prevent blossom-end rot. The fruit of affected plants is inedible and should be disposed of in your general waste. To learn more, read our article about blossom-end rot in tomatoes.

Blossom-end rot in tomatoes
Blossom-end rot is caused by a lack of calcium [Photo: Jean Faucett/]

Other tomato plant problems

In addition to the growth and development disorders mentioned, rarer tomato plant problems can also occur:

  • Tomato sunburn: Can occur when new plants have not had the chance to acclimatise sufficiently before being put into direct sunlight. Tomato sunscald is manifested by the development of papery, translucent-looking tissue changes and the fruit underneath is often watery and soft. Severely burnt leaves will fall off prematurely. You can avoid this by gradually acclimatising the plant to the heat and ensuring it has some shade.
  • Lack of fruit set: Poor light conditions, very low temperatures and high humidity can result in the fruit not setting. There are a couple of indicators to look for if you suspect there is an issue. The pale yellow sepals tend to grow particularly long and do not curl back. Alternatively, you might notice that the short, thick pollen and stigma are poorly formed. This can result in fertilisation problems with a small yield as flowers are shed prematurely.
  • Internal browning: This is the result of excessive evaporation and causes brown, dried-out tissue to form inside the tomato fruit. Excessive heat and very dry air are two of the main contributors to this problem. Internal browning often occurs if the plant has a potassium deficiency whilst being overwatered at the same time.
  • Blotchy ripening: This is when the fruit does not change colour in places when ripe and shows brown vascular veins inside. Regular watering and a good supply of potassium prevent this.

Tip: A balanced supply of nutrients can prevent many physiological disorders. A liquid fertiliser such as our Plantura Liquid Tomato Food is easy to measure out and apply when watering. The increased potassium content promotes healthy fruit development in tomatoes and many other vegetables.

Liquid Tomato Food, 800ml
Liquid Tomato Food, 800ml
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  • Perfect for tomatoes & other vegetables
  • Liquid fertiliser for healthy plant growth & an abundant harvest
  • Quick & easy application - child & pet friendly

  • Fertilisation disorders: In addition to fruit setting issues, pollination disorders can also occur due to suboptimal conditions. Extremely high or too low humidity, temperatures above 30 °C, lack of water and lack of pollinators (insects or wind movement) can lead to lack of pollination and thus to flower drop and lower yields.
  • Fruit deformities: For genetic reasons, fruits may develop appendages, also called “noses”, which usually change colour before the main fruit. Heavily ribbed and fused fruits can also occur. While you should not save tomato seed for propagation from these fruits, they are completely edible and are often an interesting feature in the garden.
Tomato with long nose-shaped deformity
Fruit deformities can lead to interesting appendages on the main fruit [Photo: 1stGallery/]