Why are my tomato plants turning yellow? This is a common question that I hear from people growing tomato plants.

One of the best parts about growing a vegetable garden is the fresh tomatoes that you'll get.  Honestly, there's nothing quite like slicing into a home-grown, juicy tomato.  Tomatoes that you grow in your home garden (or containers) seem to have better flavor, texture and color than those you can buy in the store.  It may be because they aren't being shipped and are fresh off of the plant.  It may also be because of the love that you put into growing them.

It can be disheartening to go out to the garden and realize that your tomato plants aren't thriving.  If your once dark green tomato plants are suddenly yellow, what does that mean?  They may start dropping tomatoes, which makes it even worse.  Learn what causes yellow tomato plants and how you can fix it to start growing those delicious tomatoes again.

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A healthy tomato plant should have dark green leaves and stems.  When the leaves and stems start to turn yellow, it's a sign that something is wrong.

​Take note of how the leaves are yellowing.  Are all of the leaves on the plant yellowing or just ones in certain areas?  Do they have dark spots or bugs on them?  Is the plant wilty or is it still standing upright?  Has fruit started to drop?

All of these questions can help you determine what's going on with your tomato plant. I'll break down the possible causes and the related symptoms so that you can figure out what's going on with your plant.

Tomato plants that are yellow and wilting are trying to tell you that they need some help.  Determine the most likely cause and try to fix the problem immediately to prevent the plant from dying.

Tomato plants are heavy feeders that produce a lot of fruit and can get quite large.  This means that they require a lot of sunlight, nutrients and water to keep producing.  A healthy tomato plant can get quite large, with some varieties growing into vines over 30 feet long in the right conditions.

As a tomato plant grows, the lowest leaves (also the oldest leaves), become less productive and don't produce as much energy for the plant.  These leaves naturally yellow and die back.  Since these leaves aren't contributing as much to the plant's overall productivity, the plant stops sending them nutrients, causing them to die off.  The plant sends the nutrients to leaves that are more productive in order to use their energy and nutrients most effectively.

When the top part of your plant looks full, dark green and healthy, don't worry about the occasional yellow leaves and stems on the bottom of the plant. Prune these leaves off to stop wasted resources from going to the leaves that are dying back.

​As the tomato plant grows, it will put on more leaves at the top of the plant.  Once a new set of leaves forms at the top, it's common for a set of leaves to die back at the bottom.  As long as the plant overall looks healthy and is still producing tomatoes, simply prune off the old set of leaves and don't worry about it.

When it's hot out, provide your plants with additional water.  Mulching can help prevent water from evaporating from the soil and help your tomatoes have access to water longer.

​Keep in mind that tomatoes grown in containers will have different water requirements than garden-grown tomatoes.  Plants in the garden may need more water since the water has more area to 'escape' from the root system while water in containers stays around the plant more.

Here are a few tips to keep your tomatoes watered properly:

-The best time to water tomato plants is in the morning.  The closest you can water them to dawn, the better.  This gives the leaves time to dry in case you get water on them.  Water left on the leaves during the heat of the day can cause burns.
-Water at the ground level, around the plant's perimeter, not directly at the base of the plant.  A soaker hose or tomato craters can help direct water in the right places.
-Rainwater is the best for plants.  If you have tomatoes in containers, place the containers in the rain when possible.
​-Water as your plants need it.  Tomato plants that are producing large amounts of fruit will require more water.  Water is needed more often when it's hot, but don't be tempted to water the entire plant to 'cool it down'.

Another common cause of yellowing tomato plants is the soil.  You now know that soil can affect the amount of water a tomato plant needs.  A soil that doesn't drain well can drown your plants while a soil that drains too much can prevent the plant from getting enough water.

Learn about soil textures and how they affect plant growth.

​The nutrients in the soil are also extremely important to proper tomato growth.

Nutrient deficiencies are one of the most common causes for yellowing leaves on all plants, including tomato plants.  A nutrient deficiency can occur when there isn't an adequate amount of nutrients in the soil or the plant is incapable of bringing those nutrients in.

​When the plant absorbs water, it's able to absorb nutrients.  Not enough water generally means not enough nutrients also.  Some nutrients can be over-absorbed and can block the way for other nutrients to be absorbed, causing a deficiency that way as well.

A nitrogen deficiency can be harder to detect than some of the other deficiencies.  Nitrogen causes the leaves at the base of the plant to turn yellow, which is also common in healthy plants.  The difference is seen when the plant stops growing and continues to drop leaves at the base.  The plant typically becomes less productive and produces less tomatoes.

Potassium deficiency is easier to detect.  The entire leaf doesn't turn yellow.  Instead, the space between the veins in the leaves will yellow, leaving the veins green.  There will also be some wilting in the leaves.  Treat this with potash fertilizer.

Calcium deficiency often shows itself in the form of blossom end rot.  Blossom end rot is a common tomato issue that results in the blossom end of tomatoes turning black and mushy.

To treat this, add a calcium fertilizer to the soil or directly to the plant's leaves and fruit.

Magnesium deficiency can appear similar to potassium deficiency.

​A close look at the leaf can tell you the difference between a magnesium deficiency and potassium deficiency, though

Magnesium deficiency will create small yellow spots between the veins of the leaf.  These yellow spots get larger and turn a golden color.  Eventually, they will merge and the entire leaf will turn yellow and fall off.  You may also notice a golden edge around the leaf.

​The easiest way to treat a magnesium deficiency is with epsom salt.

Sulphur deficiency affects newer leaves and growth rather than older leaves.  If the leaves at the top of your tomato plant start to turn yellow and the older leaves are fine, then you should consider adding a sulphur fertilizer (often called soil acidifier) to your plant.

Zinc also affects newer growth on the plant.  New, small leaves at the top of the plant turn yellow between the veins and crinkle up.  This results in a rosette shape rather than branched out leaves.

Tomato plants are easy to grow, but they are also easily affected by pests and diseases.  If you know what to look for, these diseases and pests are usually treatable and manageable.

Tomatoes can get diseases just like we can.  A tomato disease is usually caused by bacteria, fungi or viruses.  Tomato diseases are a common tomato plant problem.

I've outlined the most common tomato diseases that will cause yellowing leaves on your tomato plant.  If you notice that your tomato plant is having trouble but not showing yellowing leaves, you can check out these two articles for possible causes:

-10 Most Common Tomato Plant Problems
​
-Identify and Prevent Plant Illnesses

The curly top virus is caused by a viral infection that is carried by the beet leafhopper.  Don't be fooled by the name; beet leafhoppers can affect many types of plants, including tomatoes.

The leaves will curl up and roll inwards. The top part of the leaf will have small yellowed spots, but the underside of the leaf will have a purple color.  If you cut the stem open and look inside of the stem, you will probably see dark areas of dead tissue in the stem.

Leaves also get rough and may even develop some spiny protrusions.

It's hard to control curly top virus.  The beet leafhoppers transmit the virus quickly and then move on so by the time you notice the disease, apply insecticide doesn't work.  The disease isn't usually passed from plant to plant.  Remove the infected plants; they won't recover and they won't produce tomatoes.

​The best way to prevent curly top virus is to discourage the beet leafhopper from landing on your plants.  They prefer to land on plants that are well-spaced and contrast with their surroundings (i.e. tomato plants well-spaced in rich, dark soil are most susceptible).  If you live in an area where beet leafhoppers are a problem, plant tomatoes close together.  It's also a good idea to plant smaller plants between the rows of tomatoes to avoid having contrast between the soil and plant.

Tomato ringtop virus is characterized by yellow ringspots that develop on leaves.  The leaves can also turn yellow slowly, without developing spots.  You may notice that the stem ends of tomatoes can be affected as well and will develop soft, light colored spots.

The virus that causes ringtop is thought to spread two different ways.  It can be spread through pollen from infected plants to healthy plants.  It can also be transmitted from infected plants to healthy plants through nematodes that live in the soil around the tomato plant roots.

​There isn't a treatment for ringtop, so the best action is to remove diseased plants and the plants around them.

It takes infected plants some time to show symptoms, so it's a good idea to assume that the plants surrounding an infected plant are also infected.  Ringtop virus can stay in the soil for up to two years.  If you have ringtop virus, relocate your garden.

Tobacco mosaic virus was named in the late 1800s once it was discovered on the tobacco plant.  Since then, it's been known to infect many other crop plants.  Until recently, it was thought that tobacco mosaic virus was more prevalent in tomatoes.  This was until a similar virus, the tomato mosaic virus, was discovered.

It can be hard to distinguish the two from each other since they create similar symptoms.  Both diseases will cause the leaves to develop a yellow and green mosaic pattern on the leaves. Infected leaves can also curl slightly.  Plants that are infected young are stunted and produce fewer fruit.

A common way that tobacco mosaic virus is spread to tomato plants is through the hands of the gardener.  The virus can live in cigarettes and other cured tobacco products and can get on the hands.  If you smoke or use tobacco, wash your hands thoroughly before handling your tomato plants to avoid infecting them.

You can purchase tomatoes that are resistant to either tomato mosaic virus or tobacco mosaic virus.  There are a few plants that are resistant to both diseases.  When you're browsing through a seed or plant catalog, look for the following symbols to indicate disease resistance:

-TMV- indicates resistance to tobacco mosaic virus
-ToMV- indicates resistance to tomato mosaic virus

​There isn't a cure for either disease.  The best option is to remove infected plants and burn them.  Do not compost them as the virus will survive the composting process, only to be returned to garden soil later on.

Tomato yellow leaf curl is a disease that is relatively new to the U.S. It is caused by a virus and can have severe plant impacts.

The leaves will turn yellow around the margins and curl up tightly.  Plant growth is also severely stunted and plants may take on the appearance of broccoli.

There are cultivars of tomatoes that are resistant to tomato yellow leaf curl.  Look for tomatoes that have the symbol TYLCV-resistant.  The disease causes the most trouble in tropical and sub-tropical climates.  In the U.S., it has become a problem in states like California and Florida.

The disease is often carried by whiteflies, so prevention and treatment involves managing whitefly populations.  Row covers, weed management and insecticides are useful in managing tomato yellow leaf curl.

​Learn more about how to identify tomato diseases in this video:

Tomato plants are a favorite for many pests.  When left unchecked, these pests can have serious impacts on your tomato plants.  Luckily, these are mostly preventable and treatable. They are also often easier to identify than some of the tomato diseases.

Thrips are small insects that feed on the tissues of leaves.  They will leave behind scarring on the leaves, which can sometimes appear as small whiteish-yellow spots.  You may also notice black feces left behind.

You should also be able to see small yellow-colored larvae on the leaves.  Occasionally, when two tomatoes touch, thrips will feed on the area where the two tomatoes touch one another.  THey feel safe in this space.  The tomatoes will develop circles of gold flecking where the tomatoes touched.

​Plastic mulch is highly effective in preventing thrips.

Spider mites are tiny arachnids that belong to the same family as ticks and spiders.  These mites feed on the leaf tissue on the underside of the leaves.  They're very small and hard to see.  To spot them, you may need a magnifying glass.  You can also hold a white piece of paper under the leaf and shake it to cause the mites to fall onto the paper where you can identify them.

Large numbers of spider mites can remove the tissue from the surrounding leaf veins, causing a webbed appearance.  The leaves may also turn yellow and die.  You may notice clusters of spider mites at the ends of these webbed leaves. Spider mites can create webs on leaves as well.

Plastic mulch is beneficial in areas where spider mites are a problem.  Spider mites often get worse when plants are dusty and conditions are dry.  If your plants have dust on them, you can use a forceful spray of water to remove the dust from the leaves and stems.  This will also dislodge any spider mites that are hanging out on the leaf.

​If you do this, make sure that you spray the plant down early in the morning so the leaf has time to dry before the sun comes out in full force.

Whiteflies are a major nuisance for tomato growers.  They feed on the underside of leaves, causing the leaf to yellow and curl inwards.  Luckily, whiteflies are easily identified and can be seen with the naked eye.

​Whiteflies have yellow bodies and white wings.  If you shake the plant, any whiteflies on it should take to the air.

Check plants that you're going to purchase for whiteflies. Don't buy them if they have whiteflies on them.  A silver-colored plastic mulch is highly effective at preventing whiteflies while the plants are young.  You can place sticky traps at the base of the plant to reduce the breeding population.

​Spraying insecticide is not recommended since it also removes beneficial insects. Instead, encourage beneficial insects, like ladybugs, to come to your garden.  Lady bugs will feast on many tomato plant pests, including whiteflies.

Unfortunately, once leaves yellow, they won't turn green again, even if the underlying cause is treated.  Yellowing may stop, but it won't return back to the lush green color.

This depends. Leaves are responsible for absorbing sunlight and turning that sunlight into food for the plant.  Removing too many leaves can deplete the plant's energy production.  However, yellowed leaves aren't efficient at producing food and can actually suck energy from the plant.

A leaf that is entirely yellow, almost completely yellow or curled and disfigured should be removed.  If the leaf has a few small spots of yellow or the yellowing is very small, you may want to leave it on the plant temporarily. As the tomato puts on more leaves, remove damaged leaves.

​If there are pests or signs of disease on the leaf, remove it.

There are many reasons that tomato leaves turn yellow.  Sometimes it's just due to normal growth and that's ok. If you plant looks lush, healthy and is growing well, yellowed leaves at the base of the plant aren't usually cause for concern.

If you notice that the plant starts to drop fruit, slows down in growth or has severely damaged leaves, it's time to take a closer look.

When treating diseases, it's important that you remove any plants that may be infected and dispose of them properly.  Depending on the disease, consider relocating your garden next year to prevent new tomatoes from developing the same disease.

When treating pests, always opt to avoid pesticides if possible.  These remove beneficial insects that can feed on the pests.  Many pests are deflected by plastic mulch, so it may be a good idea to use plastic mulch as a preventative.

​Yellowed leaves will not turn green again and may need to be removed from the plant.
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​If you haven't yet, grab your FREE copy of the From Seed to Supper guide and learn how to start growing delicious, fresh vegetables and herbs!

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