Yellow leaves on tomato plants can be caused by several reasons. Nutritional deficiencies, plant diseases, and even the way you water tomatoes can play a part.
Getting the right answer for why there are yellow leaves on tomato plants in your garden requires lots of research and a bit of trial and error.
Tomatoes are one of the most popular garden vegetables grown by home gardeners. They are also prone to a myriad of problems, including tomatoes not turning red, bottom end rot, and leaves turning yellow. Discovering that your plants have yellow leaves can be a big disappointment and cause dismay.
Keep reading and we’ll help you narrow down the cause of yellowing leaves on your tomato plants.
Why do you have yellow leaves on tomato plants?
There are several reasons why your tomato leaves may be turning yellow. Fortunately, most of them are easily remedied.
The following list will give you the main reasons for yellowing leaves on tomato plants and show you how to fix the problems.
Don’t panic – yellow leaves are common and, in most cases, so are the solutions. We even offer a free printable to add to your garden journal.
New tomato plants with yellow leaves
Many newly purchased tomato plants will have some yellow leaves. This often happens if the plants are thin and tall and growing in a small pot before you planted them in your garden.
This yellow growth is common because nursery plants are often over-crowded or have insufficient nutrients in the small pots. New tomato plants will often develop yellow bottom leaves and this is normal.
The solution to this problem is simple – be sure to buy healthy plants. Mark downs of damaged vegetable plants with yellowing leaves are no bargain!
Not only will they continue to suffer, but they may also introduce pests and diseases that could be long-lasting problems in your garden.
Look for healthy plants with strong stems and green leaves free of yellowing or brown spots.
Even new plants without yellow leaves when you purchase them can develop some yellowing leaves soon after being planted. This is called transplant shock.
There is normally no need to be worried as long as the plant is still getting new growth. Just prune away the yellowing leaves to allow the plant to focus on new growth.
If you see only a few yellow leaves towards the bottom part of a plant that has been growing for a while, this is not usually a cause of concern. Most likely, the leaves may not be getting enough sunlight. This often happens on older plants that are bearing fruit.
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Nutritional deficiencies can cause tomato plant leaf yellowing
This common reason for yellowing leaves on tomato plants is also quite easily solved! If an established tomato plant in your garden suddenly has leaves turning yellow, a lack of nutrients in the soil may be the cause.
Tomato plants are very heavy feeders and use up the available nutrients in the soil quickly. They require lots of nutrients to grow and produce fruit.
Although a lack of nitrogen in tomato plants is a common deficiency, be sure to take care to learn which nutrient is actually needed before you add an extra dose of nitrogen fertilizer to your plants.
Soil testing kits will help you determine which nutrient is lacking and this will tell you what your tomato plant needs for extra fertilizer.
Common types of nutrient deficiencies:
- nitrogen – the entire leaf will turn yellow. Be careful about adding too much nitrogen. You’ll get lush green growth and not many tomatoes.
- potassium – the outer edge will turn yellow and then turn brown and look burned. Extra potassium will give good fruit production.
- magnesium – leaves will turn yellow with green veins. Diluted epsom salt (2 tablespoons to a gallon of water) should show improvement quickly if a lack of magnesium is your problem.
- calcium – yellow new leaves which lead to blossom end rot. Eggshells around your tomato plants can maintain a healthy calcium level. Bone meal is also another source of calcium for tomatoes.
- iron – also causes tomatoes to develop yellowing on new leaves but with green veins. Blood meal is a good source of iron.
Remember – soil testing is necessary. You cannot just go by sight and guess. Many tomato leaf diseases look similar.
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Gardener created problems
Often, the cause of tomato leaf yellowing is self inflicted by the gardeners themselves. From over-watering to under-watering or use of too much fertilizer, you may be causing the yellow leaves by the way you tend your garden.
Under-watering tomatoes may give you leaf yellowing
Tomato plants absorb nutrients from the soil through their roots when you water them. The water carries the nutrients to the parts of the plant that needs them the most.
If you do not water enough, your plants may show that they are not receiving enough nutrients by producing yellow leaves. Tomatoes need an inch of water a week early in the growing season.
Later, as they start to produce fruit, they need even more – about two inches a week.
It is best to water deeply, twice a week, rather than a little bit every day. Doing so produces roots that grow deeply in the soil. In turn, the tomato plants will be less likely to become stressed and the deep and wide roots will have an easier time finding nutrients in the soil.
Consistency is the key. For best results, water at the base of the plant and keep the leaves dry to prevent fungal diseases. Try to water early in the day if possible.
Overwatering tomatoes can also cause yellow leaves
Even though water is necessary to bring nutrients to the tomato plant, too much water is also a cause of yellow leaves on tomato plants.
One sign that you have been watering either too much or too little is when the plant produces fruits that crack open or develop blossom end rot.
Over-watering tomatoes makes the soil soggy and prevents the flow of oxygen in the soil. When this happens, the leaves turn yellow because of a lack of oxygen and the plant slowly drowns.
Don’t mulch too closely to tomato plants and be sure the soil is exposed to sunlight and air flow.
Fertilizer burn may be the cause of tomato plant yellow leaves
If you have done a soil test and determined that fertilizing is necessary, take care to follow the directions on the label. This will limit fertilizer run-off which can damage your crop.
Some labels refer to “side dressing.” This means that you should apply fertilizer next to the plant rather than directly ON them.
Too much fertilizer can create problems such as root burn. Tomato plants grown in pots can have fertilizers and salts build up in the pots leading to fertilizer burn.
When watering potted tomato plants, be sure the water drains from the holes in the bottom of the pot to wash away excess salts.
Too much sunlight can cause yellow leaves on tomato plants
Tomato plants need a lot of sunlight to grow well and produce fruit – 6-8 hours a day is recommended. However, once again, too much is not a good thing.
Hardening off the plants by gradually exposing them to the higher levels of sunlight is essential for these tomato plant seedlings.
Even plant purchased at garden centers can be prone to sunscald if left in the car on the ride home for too long. Be sure to keep the leaves away from car windows.
Sunburn on established plants is also possible, especially in hardiness zones that have very hot days and high temperatures. Tomatoes in west and south-facing sites may benefit with the protection of shade cloth on the hottest days.
Be careful about too much compost
Normally, adding compost to tomato plants is a good thing, but it is also possible for too much of it to cause yellow leaves on tomato plants.
The reason is that compost high in carbon can actually rob the soil of nitrogen which is necessary to feed your tomato plants.
If you do add compost, be sure to mix it well into the soil and be mindful of the proper ratio of green to brown when creating a compost pile.
Soil pH problems can cause yellowing leaves on tomato plants
Your soil’s chemical composition is very important when you grow tomatoes. This is measured by the soil’s pH level.
The pH level can range from acidic to alkaline and is measured on a scale from 0 to 14 with low numbers being acidic and high numbers alkaline. 7 is considered neutral soil pH.
Tomato plants grow best in well draining soil with a soil pH that is slightly acidic – a range of 6.2 to 6.8 is recommended. Levels much lower or higher than this number can be the cause of yellowing leaves.
There are a few ways to test your soil pH level. You can send a sample of your soil to a lab for testing, (contact your local agriculture extension office) or purchase a kit to test your soil.
If your soil is too alkaline, adding compost will help. The addition of limestone will help overly acidic soils.
No one likes to spend their summer weeding a vegetable garden. As tempting as it might be to reach for a herbicide, remember that the deep roots of tomato plants are very sensitive to chemical weed control products.
Even if you don’t use a weed killer directly around the tomato plant, the roots can still bring some of it to the plant, resulting in stunted growth and yellow leaves.
The solution is simple – manage weeds by hand! Mulching helps to keep weeds away and close spacing of tomato plants will also limit weeds.
Garden pests can cause leaves turning yellow on tomato plants
There are a number of garden pests that can cause the leaves on your tomato plants to turn yellow. Some common smaller ones are:
- spider mites – you may not see them, but might notice fine spider webs on your plants. Pick off heavily infected leaves and wash the rest of the plant with a mild soapy water mixture.
- thrips – they puncture the leaves and suck on them, causing speckled yellowing of the leaves. Insecticidal soaps are effective in controlling them.
- potato aphids – leaves yellow and go brown from the top down. Neem oil is effective in treating them.
- flea beetles – they make tiny holes in the leaves and the leaves go yellow. Planting chrysanthemums near tomato plants will limit them.
- nematodes – these cause swelling and growths on the roots and can cause yellowing leaves that wilt and stunted growth of the plant. Good crop rotation will prevent nematodes from infecting your tomato plants.
Good garden maintenance will keep pests at bay. Inspect new plants before adding them to the garden, and clean out crop debris from the garden. Remove weeds from surrounding areas so you won’t have an area that will host pests.
Larger insects such as tomato horn worms and cutworms can be easily picked off.
Fungal diseases and viral diseases often cause yellow leaves
One harder to treat reason for yellow tomato leaves is a plant that has developed a fungal disease.
These are the main fungal diseases that may infect your plant:
- Early blight on tomatoes – tomato blight leaves are yellow with small spots that continue to enlarge.
- Tomato blight late – more of a problem since it affects the upper leaves of the tomato plant.
- Fusarium wilt – shows as yellow leaves on one side and stunts the growth of the plant, which affects fruit production.
- Verticillium wilt – yellowing leaves develop on older plants later in the season.
- Tomato mosaic virus – curling leaves and yellow mottling on the leaves.
- Tomato leaf curl virus – white flies cause this virus. Symptoms are yellow leaf margins, stunted growth of leaves and upward curling.
Each disease has its own method of treatment. Determining whether your plant is infected by a fungal disease or viral disease may require you to reach out to your local agricultural extension service for help.
Yellowing leaves at the end of the season
An unexpected frost can cause the leaves of tomato plants to turn yellow. Removing the affected leaves will allow the plant to recover.
However, if fall is approaching when you notice that your tomato plants are developing yellow leaves, there is no reason to worry – Mother Nature is doing what she does best – putting your garden to bed!
Now is the time to pick off any green tomatoes if you have not already done so. They will ripen indoors!
Don’t let yellow leaves on tomato plant wreck your harvest. With proper watering, making sure that your plant has the right nutrients, and the use of correct gardening techniques, most yellow leaf problems can be treated or prevented.
Get the tomato leaf yellowing printable
Our printable shows the causes of yellow leaves on tomato plants and ways to fix them.
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