The skillful cultivation of tomatoes rests on several supporting pillars. If only one of them is out of balance, the longed-for harvest of crisp, fresh apples of paradise is at stake. Yellow leaves are one of the most common symptoms of damage to tomato plants and signal serious complications. This does not necessarily have to be a disease or a pest infestation. Various deficiency symptoms also reveal themselves in this way. Find out here about possible causes and effective solutions for yellow leaves on tomatoes.
Unsuitable light and temperature conditions
For a tomato plant to thrive vigorously, it needs every ray of sunlight it can get in the local climate. In addition, warm temperatures of significantly more than 15 degrees Celsius play an important role. If you assign the tropical plant to a location that is too dark and cool, photosynthesis will come to a standstill. The result is yellow leaves on long shoots.
Solution: Sunny, warm location
Tomato plants in a container are best moved immediately to a sunny place, which is warm and protected at the same time. Here, the nightshade plant should recover within a short time. On tomatoes in the bed, take a look at the closer neighborhood. If there are specimens that cast shade on the plant, either cut them back or remove them completely.
In view of a temperature minimum of 15 degrees Celsius, young tomatoes are not allowed outdoors until mid-May at the earliest. Consequently, amateur gardeners prefer the plants behind glass, so that they can cope with the limited time in the bed due to a head start on growth. Meanwhile, the move from the room or greenhouse to the fresh air exerts considerable stress on the tomato plants, which in the worst case leads to yellow leaves.
Solution: hardening off
Start preparing the young tomatoes for the open ground already from the beginning of May. During the day, place the plants in a semi-shaded, sheltered place on the balcony or in the garden. In the evening, carry the pots back indoors. In this way, your seedlings will gradually get used to the climatic conditions outdoors and will be ready when the sun shines on them from mid/late May.
Tomatoes are among the highly nutritious plants. Even in nutritious, humus-rich soil, the plants are at a loss without additional nutrient supply. If the young leaves turn yellow, there is a lack of iron, zinc and copper. If older leaves take on a yellow color, this circumstance indicates a deficit in the supply of potassium, magnesium and phosphorus. If you are confronted with the damage, although you always attach importance to a balanced fertilization, the plant lacks lime.
Solution: Balanced organic fertilization
Since in the private kitchen garden fertilizers with chemical components are frowned upon, adjust the nutrient supply to the following parameters in the case of yellow leaves:
- Fertilize every 14 days with compost and horn shavings until the beginning of flowering.
- Alternatively fertilize with horse manure, guano or nettle liquid manure
- In addition, if the leaves are yellow, apply activated lime or rock flour every 2-3 weeks.
- After the beginning of flowering until fruit ripening, fertilize weekly with organic fertilizer.
- In the tub fertilize with organic liquid preparation for tomatoes
You can effectively prevent yellow leaves on tomatoes if you mulch from the beginning with nettle and comfrey leaves, mixed with the staked out foliage of the tomato plants.
Tip: A green manure in the previous year perfectly prepares the bed for tomatoes, so that yellow leaves do not appear in the first place. Well suited are seed mixtures, such as ‘bee friend’ or ‘marigolds’. In the weeks before planting, starting in mid-May, mow down the green manure plants and rake them under
Tomatoes prefer a consistently moist substrate, without extreme swings in either direction. If there is an oversupply of water, the plant reacts to it with yellow leaves, while dryness results in brown discoloration. Both in the bed and in the tub, waterlogging poses the greatest danger in this respect, as experience shows that amateur gardeners tend to water too much rather than too little. As a result, the roots rot, so that the transport of nutrients comes to a standstill, which manifests itself in yellow leaves.
Solution: Well-balanced water balance
To ensure that a tomato plant does not suffer from an over-supply of moisture and the resulting yellow leaves, the following measures serve as an acute and preventive treatment:
- Cut off the yellow leaves at the first symptoms
- Do not water the plant until the thumb test detects a dried substrate
- Protect against too much wetness from above with a rain cover or transparent hood
- Repot tomatoes in containers in fresh, dry substrate
Drainage acts as an effective precaution against waterlogging in the bed and tub. For this purpose, spread some shards of clay or pebbles in the planting pit or above the water drainage in the tub before planting. If you also mulch with straw, nettle leaves or grass clippings, this measure will keep the soil moist and warm longer.
Leaf spot disease (Septoria lycopersici).
If site problems and neglect in care can be ruled out as causes, a widespread plant disease on tomatoes comes into focus. Especially during rainy, muggy summers, the sword of Damocles of leaf spot disease dangles over the apples of paradise. Yellow leaves are among the first symptoms of the dreaded fungal infection. As the disease progresses, watery spots with black edges form on the yellow foliage. Eventually, the leaves fall off and the supply of fruit comes to a standstill.
Solution: control with natural means
Since the use of a chemical fungicide on tomatoes is out of the question, use natural means to combat leaf spot disease this way:
- Remove all yellowed leaves and dispose of them in the household trash.
- Spray the plant itself and neighboring tomatoes with a mix of fresh milk and water (1:2)
- Consistently prune the plant at least once a week
- Even at planting time, make sure tomatoes are spaced airy from each other so rainwater dries off faster. Ideally, protect outdoor plants with a rain cover or enclose them with a tomato house.
Bacterial wilt (Corynebacterium michiganense)
If tomato leaves take on a yellow color from below, while at the same time brown-yellow vessels appear in cut shoots, bacterial wilt has struck. If the disease progresses further, the yellow leaves turn brown and fall off. Unlike leaf spot disease, this infection spreads to the fruit. In the early stages of infestation, there is still a chance of saving the plant.
Solution: intervene quickly or complete disposal
How to proceed:
- Rigorously cut off and destroy all yellow leaves and infected shoots.
- Clear away mulch and thoroughly loosen the soil
- Sand compacted soil and optimize with compost
- Do not apply nitrogen-rich mineral fertilizers
- Administer strengthening agents, such as Neudovital and liverwort extract
If more than 30 percent of the leaves have already turned yellow, the disease threatens to spread further in the garden. In this case, dispose of the entire plant and maintain a 4-year rotation before reestablishing tomatoes at that location.
Tomatoes in greenhouses and containers are among the prey of thrips. The tiny fringed aphids, also known as thunderflies, cause yellow leaves on tomatoes as part of their nefarious activity. The adult pests suck the plant sap, while the larvae feast on the roots.
Solution: soft soap solution, primary rock flour and beneficial insects.
To get rid of the tiny insects, it is unnecessary to reach for the chemical club. Instead, fight the pest with the classic soft soap solution. To do this, mix 15 ml of pure soft soap or curd soap in 1 liter of water to repeatedly spray the infested plant. Since moisture on the foliage of tomato plants is not welcome, primitive rock flour serves as a practical alternative in case of doubt. With the help of a powder sprayer, apply the agent every 2-3 days until no more thrips swarm around.
Thrips are particularly common on tomato plants in greenhouses. In this protected environment, health- and environment-conscious hobby gardeners get animal protection help. Beneficial insects, such as predatory mites and hoverflies, love to eat the thrips. The specialized specialized trade offers the helpful insects, which are completely uncomplicatedly brought out, in order to migrate after done work finally from the greenhouse.
Whiteflies (Trialeurodes vaporariorum)
The powdery white flies are actually pretty to look at, but cause considerable damage to tomato plants in the greenhouse. In fact, they are moth scale insects that cover their yellowish, 1-5 mm small body with white wings. Introduced from South America, the pests spread explosively in the warm climate of the greenhouse, while sucking the life out of the tomato plants. As a result, the leaves turn yellow as they increasingly lack nutrients. In addition, the foliage is covered with a sticky layer of honeydew, which attracts ants in droves.
Solution: yellow boards, attractant traps, ichneumon wasps.
At the first sign of whiteflies in the greenhouse, trap the adults with yellow boards. If the occurrence of whiteflies is still limited, you can put an end to the infestation with attractant traps. These are sticky traps equipped with pheromones that attract and hold the sexually mature insects. Close-meshed insect nets protect individual tomato plants from infestation. The application of ichneumon wasps has proven to be an effective biological control measure. In particular, the pea wasp Encarsia formosa targets the larvae to parasitize them. Two-spotted ladybugs and lacewings also take on the pests with gusto.
Growing tomatoes is undoubtedly one of the most demanding challenges in the hobby garden. However, the reward for all the efforts is an incomparable pleasure for the gardener, which tomatoes from the store shelf can’t even begin to match. So don’t throw in the towel as soon as yellow leaves appear on tomatoes. Instead, start a dedicated search for the cause. Often the problem can be solved by simple measures, such as a change of location, a change in watering behavior or an adapted nutrient supply. If an infestation with fungi, bacteria or pests turns out to be the trigger, various natural control agents are available. You can read about the most common causes and possible solutions here, so that you do not have to do without home-grown apples of paradise.