Mad About Berries

Why Are My Tomato Leaves Turning Yellow?

Growing fresh tomatoes is the dream of every green thumb enthusiast, but there are a lot of hiccups you’re going to have to deal with along your journey. One of the most common problems is when the leaves turn yellow. What causes tomato leaves to turn yellow, and how can you fix it?

Yellowing leaves are very commonly associated with improper watering habits or transplant shock. Most often, tomato leaves will start to yellow when the plant is being overwatered and suffering from rot.

There are a number of reasons why your tomato plant leaves are turning yellow, but the most important thing is not to panic and work yourself up about it.

It’s a very common problem that most tomato growers will experience at some point, but thankfully, the remedies are quite simple. The rest of this article will discuss why your tomato plant leaves are yellowing and what to do about it.

Published: November 12, 2022.

tomato leaves yellow blight 1

What Causes Tomato Leaves to Yellow?

If you have any gardening experience, then you’re probably aware that yellowing leaves aren’t a good sign. Often, they indicate a problem with the nutrition or physiology of the plant.

Certain environmental conditions and diseases can cause this problem to occur as well. The following can also be responsible for your tomato leaves turning yellow:

  • Natural development
  • Poor watering habits
  • Diseases
  • Pests
  • Nutrient deficiency
  • Transplanting
  • Poor aeration

Most of these problems can be simple to remedy with some proper care and attention.

Natural Development

During the early stages of tomato seedling, you’re likely to focus a lot more on your plant to make sure it thrives. As such, when you see decaying yellow leaves, you might start to worry whether something’s wrong.

Cotyledon leaves are grown by seedlings for the sole purpose of providing nutrients for the plant to grow. Once done, these leaves will start to yellow and fall off, allowing the true leaves to take over the role of providing nutrients to your plant.

If your tomato seedlings look healthy otherwise, then it’s likely that the yellowing you’re seeing is the cotyledon leaves falling off, which is completely natural.

Poor Watering Habits

Everyone’s done it at some point. Over or underwatering your plant is really easy to do, especially if you’re new to gardening as a whole. Even experienced gardeners often find it challenging to get the perfect balance for their plants.

Incorrect watering patterns are the most common cause of yellowing leaves, as well as other problems with your tomato plants.

While they are listed as being easy to grow, tomatoes have pretty delicate roots and tend to be finicky when it comes to getting the perfect amount of water for their needs. Too much, and you risk flooding the roots.

Too little, and the plant isn’t getting the nutrients it needs. It’s a difficult balance to find, but in general, 2” every 2-3 days is a good baseline for tomato plants in the ground.

Potted tomato plants should get more, and you’ll need to adjust your number based on environmental factors such as wind, heat, and humidity.

watering tomato plant

A water gauge or marker plant can help you figure out the precise amount that works for your tomatoes. It’s worth noting that overwatering is a much more common problem with plants across the board, and we’re all guilty of it from time to time.

With overwatering, you’ll start to notice the leaves yellowing and falling off as a result of rot, while underwatering will cause wilting long before the leaves change colors.

Overwatering is also much more dangerous and difficult to remedy. Once you have the dreaded root rot, you might be at the point of no return, although there are some remedies you can try to salvage the situation.

Water your plants slowly and consistently, letting the water stream into the soil (not the top of the plant) for the best results.

Diseases

Although less common, diseases can cause your leaves to turn yellow as an indicator that you’re plants aren’t doing too well. Soil-based diseases are common and can be transferred to your tomato through several means, including soil splash and leaves touching the ground.

To prevent the risk of diseases, keep your soil at 6.5 pH, mulch around your plants, and prune often. If you diagnose any kind of fungal disease, you will need to completely remove any affected soil before planting again.

Not doing so will reintroduce your plants to the same fungal infection afflicting them in the first place. Here are some of the most common diseases you’ll encounter on your tomato-growing journey.

  • Blight
  • Septoria leaf spot
  • Verticillium wilt
  • Fusarium wilt

Each of these can affect the root or leaves of your tomato plant and cause it to perish. If you suspect a disease, it’s worth looking into these four most common fungal diseases to make a diagnosis and establish a course of treatment.

Pests

Pests are something you’ll probably have to deal with season after season, and if your tomato plant is being victimized by aggressive pests, its leaves will inevitably begin to yellow. Be on the lookout for the following pests:

  • Aphids
  • Thrips
  • Whiteflies
  • Spider mites
  • Flea beetles
  • Cutworms

Each one of these pests can be detrimental to your tomato plants and anything else in your garden for that matter.

One way that you can start to detect the presence of pests plaguing your plants other than simply observing them around your garden is to examine your yellowed leaves closely. If you notice that the yellowing is localized around a particular area, then it’s likely you’re dealing with pests.

Unlike a disease, which generally spreads from bottom to top, or a lack of nutrients, which generally evidences itself by an overall yellowish appearance, pest-afflicted tomato plants will yellow in areas of distress.

To remedy the issue of pests, create a biodiverse environment where predators can thrive. Spiders, ladybugs, and wasps are all great allies in the fight against pests and can do a lot of the work for you when it comes to stopping your pest problems.

You can, of course, try to get rid of pests by hand, and if you’re vigilant, you may be able to catch the problem before it becomes a major infestation.

Nutrient Deficiency

Tomato plants require plenty of macronutrients to stay healthy, including nitrogen, potassium, and phosphorus, as well as a number of micronutrients.

Yellowing leaves can be an early warning sign that your plant isn’t getting the nutrients they need or that the roots aren’t adequately meeting the demands of the plant.

Of all of the macro and micronutrients that your tomato can be deficient in, nitrogen is the most common.

tomato leaves yellow

Often, you can detect nitrogen-poor soil by the leaves turning yellow. If the leaves at the bottom are yellowing while the leaves at the top are still bright green, then it’s possible you have a nutrient deficiency in your hand.

Fertilize throughout the growing season to make sure your plants get the nutrients they need.

It’s also worth looking into root rot again as another cause of the nutrient deficiency. If the roots aren’t able to get nutrients to the rest of the plant, then your leaves will start to yellow.

Uncovering root rot is never a pleasant discovery, but once you’ve found it, salvage the plant if possible or uproot and start anew.

Transplanting

Another common cause of yellowing across your leaves is transplanting. If you’ve just repotted your tomato plant and noticed yellowing leaves, then it’s probably nothing to worry about. Tomatoes have quite delicate roots, so a little bit of transplant shock is inevitable.

Do not break up the roots on your tomato plants; it will not encourage it to grow. The roots are prone to damage quite easily, but thankfully, even if you’ve made this mistake, then with a little patience, your plant will recover.

Just make sure not to stress it out with any other stresses during the recovery process, or you may have more serious matters to deal with.

Poor Soil Aeration

Soil compaction can cause the oxygen to be nutrient-deprived and makes the job of transporting oxygen much more difficult for the roots.

If you leave the plant in poorly aerated soil, it will die eventually. Compacted, dense soil can damage your plant and cause the root systems to struggle.

earth worms

To avoid this, plant your tomatoes in good soil enriched with organic matter to create a garden biome. Since stepping around your plants can cause compaction, consider planting your tomatoes in raised beds for the best results.

Most tomato growing problems can be avoided by adding compost and worm casting into the soil before planting the tomatoes. Also, compost and worm casting can be added during the growing season - they enrich the soil with nutrients, aerate the soil, make it hold more moisture, and also improves drainage.


Final Thoughts

There are a number of causes for your leaves yellowing, but most of them can be easily remedied with a little detective work.

Always make sure you’re paying attention to what your plant is telling you by observing how the yellowing occurs—this can often point you in the right direction.

Make sure you fertilize, aerate, and water your plant as needed to keep your tomato plants healthy and growing all season long!



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