A lush green yard can represent a major monetary investment in the value of your home. For this reason, when you discover tomato leaves turning yellow it can be extremely disappointing. Why do they all of a sudden start turning yellow and start dying?
- What causes this?
- Do you just have poor soil?
- Are your gardening care practices wanting?
In this article, we will explore these questions and provide some sound advice on proper soil amendment and good plant care practices to help you keep your green plants green. Read on to learn more.
Why Are My Tomato Leaves Turning Yellow?
Many gardeners enjoy growing tomato plants, which often thrive without much attention, especially when planted in places with plenty of sunshine and water.
However, tomato plants can easily succumb to a number of problems, landing their caretakers in a world of despair. Considering all their trouble, it’s a wonder many people still grow them.
What Causes Yellow Leaves on a Tomato Plant?
What do yellow leaves on tomato plants suggest?
Well, tomato plant leaves turn yellow for a number of reasons. However, yellow tomato leaves don’t necessarily mean that the plant is failing.
Tomato plants that turn yellow on their stems, leaves, or fruits may suffer from a pest infestation, disease, or extreme temperatures, which can ultimately affect the quality of the yield.
Some situations can also lead to yellow leaves, such as nitrogen deficiencies in the soil, over watering, under watering, or insufficient sunlight on the bottom leaves.
Let us look at each of these causes, and hopefully, you will find one or a combination that could help you come up with a proper solution.
Yellow Leaves: Probably Nothing To Worry About
Tomato leaves yellowing at the bottom of the plant are not necessarily a call for trouble.
The lower leaves on a large, bushy, mature plants may display brown spots, might not receive sufficient sunlight, causing them to turn yellow. This is really nothing to worry about.
Fungal diseases like:
- Early blight
- Late blight
- Blossom-end rot
- Tomato yellow leaf curl virus
- Verticillium Wilt (treatment)
- Fusarium Wilt (treatment)
… all usually cause yellowing.
The ‘yellowing’ starts from the lower leaves, making their way up to the top of the plant. When these tomato diseases are left untreated, the plant may eventually die.
Wilt diseases mostly thrive under wet conditions and hosted by nearby weeds. You can control wilt diseases by regularly applying fungicides to your tomato plants. When the problem persists, you should consider using wilt resistant cultivars for future projects.
Related Reading: Learn more about Leaf Spot Alternaria here.
Pests such as the Psyllid insect and tomato hornworms usually feed on the leaves, and in the process, inject toxic saliva into the plant, causing the leaves to turn yellow. Stems might also become crooked, and the leaves develop purple tinged veins.
To confirm a psyllid infestation, check the leaves’ underside for nymphs. To prevent the problem, it’s recommended to dust the foliage with Sulfur. A spider mite attack could also cause yellow striplings on the leaves. An insecticidal soap can help alleviate the problem.
Insufficient nitrogen in the soil
You also need to check the amount of nitrogen in your soil. Nitrogen is essentially the element that gives plants the dark green color, and enhances healthy growth.
Nitrogen deficiency in the soil will cause the leaves of plants (including your tomato plants) to turn yellow or gain spots.
Test the amount of nitrogen and other nutrients in the soil, but be careful not to add excess nitrogen, as it could actually “burn” the plant.
Too much nitrogen could also make your tomato plants to be bushy and beautiful, but bear no fruits.
Heat is also a culprit when it comes to yellowing in leaves and fruits. This is commonly referred to as “solar yellowing” or “yellow shoulders”.
Yellow shoulders usually occur when the fruit are beginning to ripen, followed by a rise in temperatures above 86 degrees Fahrenheit.
Half of the tomato fruit ripens into red, while the upper half turns yellow. In exposed, hot locations, sunscald may occur, causing the fruit to turn white or yellowy, with a sunken-in leathery appearance.
Yellowing caused by heat usually occurs when the plant lacks enough leaves to protect the plant.
To prevent this, control and monitor foliage harming tomato plant diseases such as the Curly top virus, and the Ring top virus.
The virus will actually show signs of yellowing leaves that tend to curl upwards. Also, leave plenty of leaves on your tomato plant when pruning.
Tomatoes are also sensitive to cold. Cool and rainy climates could thicken the lower leaves, which will in turn roll.
However, this is a stress response that doesn’t cause permanent damage or interfere with fruit production. New foliage will grow in warmer weather, and the plant won’t be affected.
How much are you Watering?
If the plant does not receive adequate water, its yellow leaves can start at the bottom of the plant. Tomato plants require watering especially when they are young seedlings or after they are transplanted into the garden.
The tomato plant will also require watering during the hot seasons, especially when the plant is bearing fruit. In most case, a good, deep watering a day will do when bearing fruit, or in hot temperatures.
Be careful since over-watering can actually cause leaves to turn yellow at the bottom. At times, this can be hard to control, especially in rainy areas.
For this reason, it’s imperative that you have a good mulch around your plants, and use well-draining soil that doesn’t develop puddles when watered. If drainage is an issue, a transplant mix or compost can help.
What Should You Do To Prevent Tomato Leaves Turning Yellow?
As soon as you pick up the plant from the nursery, you should start a pest and disease prevention routine. Be sure to look for dark green, stocky plants with thick, stiff stems and no signs of leaf spotting or yellowing.
Don’t purchase any plants already flowering or bearing fruit, since they have a harder time adapting to the new home than younger plants. In general, tomatoes will do well in a minimum of about 6 hours on direct sunlight.
You should also allow about 2 feet spacing between small plants, and for the larger plants, spacing should be up to 4 feet. This is essential as it allows air to circulate between the plants and through the leaves, which helps to prevent fungus.
When possible, water the plants from the base, preferably using either a watering can or a drip irrigation system.
For regular sprinklers that water the entire plant, do the watering in the morning to allow the plants to dry out before sun down.
You can also prevent infections by choosing the proper type of tomato, as many are resistant to some fungal infections.
Now let’s look at some general reasons yellow leaves begin showing up on plants.
Is Your Soil Bad?
Very often, inexperienced gardeners and first time cannabis growers write off their poor plant performance to poor soil conditions. While this may be a part of the problem, it’s important to understand that poor soil conditions can certainly be corrected.
If your soil:
- Lacks in nutrients
- Holds an unusually high pH level
- Drains poorly
… you can expect your plants to suffer; however, you can also reasonably expect to be able to correct these problems.
Very hard and compacted soil (such as clay soil) should be well tilled and amended with compost to improve drainage and reduce soil compaction.
Once the basic soil has been treated in this way, remember that when you add new plants and trees, you should dig ample and generous holes and fill them with a loose mixture of your native soil, compost and your chosen organic or chemical fertilizer.
Tomato Tip: We always plant tomatoes with Epsom salts in the planting hole
When you start your plants off with a loose, rich, well-drained soil you give them a much better chance of thriving. Once your plants become established, add a gypsum soil enhancer a couple of times a year to keep the soil in good condition.
Are You Watering Too Much?
Remember that yellowing leaves is one of the basic symptoms for lack of calcium. If you water too much, you will wash the calcium away from the soil and prevent your plants from being able to take up enough calcium to thrive.
To prevent this problem, you must learn how to water properly. It is tempting to water very frequently and lightly; however, this is exactly the wrong way to do it. Instead, learn to water infrequently and deeply.
By allowing the soil to become slightly dry between watering and then watering slowly, over an extended period of time, you encourage the plants’ roots to stretch out in search of water. This helps your plants establish themselves more quickly and with a lesser amount of stress.
Just keep in mind that if you see your plants’ leaves beginning to yellow or becoming yellow with green veins (chlorosis) you should resist your immediate impulse to water.
Over-watering will only make these conditions worse. Instead, you must establish a regular watering schedule (weekly is good) and apply soil amendments on a regular basis.
Note that if your plants are experiencing chlorosis, you may wish to give them a dose of a chelated iron supplement; however, you must remember that your soil needs to have good nitrogen content in order to activate iron supplementation.
If your soil is very compacted and has a high clay content, you may also wish to amend it with soil sulfur a couple of times yearly to reduce its acidity.
Other Reasons For Yellow Leaves
In addition to soil and watering problems, there are a few other reasons why leaves may turn yellow. Among them are:
- Infectious diseases such as bacteria and fungus may cause your leaves to yellow.
- Insect pests may suck the life out of your plants and cause yellowing.
- Excessive fertilizer may burn the plant leaves and cause brown spots and yellowing.
- Inadequate lighting can interfere with photosynthesis.
- Excessive heat or cold can cause yellowing of leaves.
Leaves Turning Yellow? Don’t Overreact!
Remember that leaves do naturally turn yellow as they mature, age and prepare to fall off. Occasional yellowing of leaves is nothing to be concerned about. If you do notice your plants leaves yellowing rapidly and en masse, refer to the tips presented here to correct the problem.