Why are my tomato seedlings turning yellow?

Yellow Seedling Leaves – Why Are My Seedlings Turning Yellow

Have you started seedlings indoors that began healthy and green, but all of a sudden your seedling leaves turned yellow when you weren’t looking? It’s a common occurrence, and it may or may not be a problem. Keep reading to learn more about yellowing seedling plants and how to treat them.

Yellow Seedling Leaves

The first thing to establish is which of your seedling leaves turned yellow. When seedlings emerge from the soil, they put forth two starter leaves called cotyledons. After the plant becomes more established, it will begin producing differently shaped leaves that are characteristic of its species.

The cotyledons are designed to get the plant started in the very beginning of its life, and once it’s producing more leaves, these aren’t really needed anymore and will often yellow and eventually fall off. If these are your only yellow seedling leaves, your plants are perfectly healthy.

Why are My Seedlings Turning Yellow?

If it’s the larger, more mature leaves that are turning yellow, you do have a problem, and it could be caused by any number of things.

Are you giving your seedlings the right amount and intensity of light? You don’t need to buy a fancy grow light for healthy seedlings, but the bulb you do use should be trained about as close as possible directly over your plants and attached to a timer that keeps it on for at least 12 hours per day. Make sure you do give your plants a period of darkness too, of at least eight hours.

Just as too much or not enough light can cause yellowing seedling plants, too much or too little water or fertilizer could also be the problem. If the soil around your plants has been completely dried out between waterings, your seedlings are probably just thirsty. Overwatering, however, is a very common cause of sickly plants. Let the soil begin to dry a bit between waterings. If you’re watering every day, you may very well be doing too much.

If water and light don’t seem to be the problem, you should think about fertilizer. Seedlings don’t necessarily need fertilizer so early in their lives, so if you’ve been applying it regularly, that may be the problem. Minerals from fertilizer can build up very quickly in seedlings’ small containers, effectively strangling the plants. If you’ve applied a lot of fertilizer and can see white deposits around the drainage holes, flush the plant gradually with water and don’t apply any more fertilizer. If you haven’t applied any and your plant is yellowing, try a single application to see if it perks up.

If all else fails, plant your seedlings in your garden. New soil and steady sunlight might be just what they need.

One of the questions tomato growers frequently ask is “why do my tomato leaves turn yellow?”.

There are many possible reasons why tomato leaves might turn yellow. These include excessive watering, nutrient deficiencies, fungal diseases and viral diseases.

The yellowing pattern and the location on the tomato plant where leaves turn yellow can help identify the cause of this problem. Try answering the following questions:

Are there spots on the leaves?

Are there any additional symptoms, such as necrosis, tip burn or wilting?

Does the yellowing of leaves first appeared on lower or on upper leaves?

What is the pattern of the yellowing – Does the entire leaf become yellow uniformly?

Is it interveinal chlorosis? Are there yellow patches on the leaves? Is the yellowing around necrotic spots? Is it a mosaic?

Sometimes it is not easy to spot the differences and accurately respond to these questions. However, it is well worth the effort, because recognizing the correct reason why tomato leaves turn yellow will help choosing the correct treatment.


When too much water is applied, water replaces oxygen in the soil. The lack of oxygen kills roots so they are unable to absorb water and nutrients.

As a result, leaves become soft and turn yellow uniformly, i.e. the entire leaf turns yellow. Excessive irrigation does not only turn tomato leaves yellow, but also causes cracked tomato fruits, wilting of the plant and blossom end rot.


Deficiencies of some nutrients might result in leaf yellowing of tomato plants. The position of the yellowing leaves on the plant and the yellowing pattern can tell a lot about the possible causes.

Nitrogen deficiency – older tomato leaves turn pale and yellow first. Yellowing gradually spreads to younger leaves.

Sulfur deficiency – symptoms resemble nitrogen deficiency, where tomato leaves become uniformly pale green or yellow. In contrast to nitrogen deficiency, sulfur deficiency symptoms appear on the upper leaves first and progress towards lower leaves, until the entire plant appears uniformly chlorotic.

Iron deficiency in tomato is characterized by interveinal chlorosis of younger leaves and chlorosis at the base of the leaf. Severe iron deficiency results in leaves becoming completely bleached (very pale yellow).

Magnesium deficiency in tomato plants also results in leaf yellowing. Interveinal chlorosis begins near the margins of older leaves and spread towards the middle of the leaf. Brown necrotic spots may also develop in between veins of leaves that show symptoms.

In potassium deficiency, the edges of older leaves become chlorotic and at a more advanced stage, tomato leaf tips and edges develop a brown necrosis.


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Unlike in nutrient deficiencies, yellowing of tomato leaves which is a result of a fungal disease is not uniform in pattern and distribution over the leaf. Chlorosis may appear around lesions and leaf spots, on one side of the plant, one side of the leaf etc.

Verticillium wilt – symptoms include V-shaped yellow lesions between veins, that progress to brown lesions. Symptoms first appear on lower leaves, starting from the margin of the leaves. This disease is favored by cool temperatures.

Fusarium wilt causes yellowing of leaves usually on one side of the tomato plant. Older leaves will show symptoms first. As the disease progresses, branches wilt.


Various viral diseases of tomato cause leaf yellowing.

For example, symptoms of ToCV (Tomato Chlorosis Virus) and TICV (Tomato Infectious Chlorosis Virus) start with interveinal chlorosis of older leaves. These symptoms can be easily confused with magnesium deficiency symptoms. As the disease progresses, leaves start to thicken and roll up.

Tomato Yellow Leaf Curl Virus (TYLCV) c uses severe damage to tomato. Symptoms include stunting, curling and yellowing of leaves. These viruses are transmitted by whitefly.

Interveinal chlorosis and leaf curl in tomato, caused by Tomato Chlorosis Virus

To summarize, there could be many reasons why tomato leaves may turn yellow. Paying attention to the exact pattern of the symptoms and having knowledge of the conditions that affect the possible causes is the key to correct identification and treatment.

Seedlings Turning YellowYellow Seedling Leaves

A grow light specifically designed for horticultural applications is best, but not always feasible or cost effective. The lighting you use should be as close as possible to the plants without burning or drying them out. They also need a day-night cycle. Most plants require 10 – 12 hours of light daily for optimal growth, some will get by on less. 6 – 8 hours of darkness is also required.

3. Moisture is critical to the development of all plants. Excessive moisture or inadequate watering are other possible causes for the leaves to be turning yellow. Allow the soil to dry out between waterings and it should never be constantly wet.

Plant Disease

4. An unlikely scenario for the yellowing of your plants could be a fungus or mold. If the soil is kept overly moist this at times occurs. If there is inadequate air circulation it happens even more often. If the mold is whitish – it could be damping off. If it is just a light green to yellow it can generally be reversed before it depletes oxygen in the soil and suffocates the roots.Place a fan on low, at a safe distance from the plants to provide a gentle breeze.

Marijuana Seedling Problems

When your marijuana plant is a seedling, it is in its most important and most vulnerable stage of life. This means you will need to be well acquainted with the potential problems that could occur so as to ensure a healthy beginning and future of your plant’s life.

About marijuana seedling problems

  • Overwatering seedlings
  • Underwatering seedlings
  • Nutrient problems
  • High temperatures
  • Improper lighting
  • Marijuana plant symptoms

‘Water and heat are critical at this point of development. The new, fragile root system is very small and requires a small but constant supply of water and warmth.’ ~ Jorge Cervantes

The most common seedling are overwatering, underwatering, nutrient problems, temperature, and lighting issues. These are all preventable conditions that an educated or experienced grower will effectively avoid, but as a new grower you can also prevent them from occurring just by doing your homework.

Overwatering seedlings

Overwatered Marijuana Seedling – Image Powered by growweedeasy.com

Although we refer to it as “overwatering,” the problem itself comes from a lack of oxygen rather than an overabundance of water. Hydroponics systems, where plants are literally “planted” in water, work perfectly fine as long as there is enough dissolved oxygen in the water. If you are growing your seedlings in a container as many growers do, overwatering can be seriously risky to your marijuana plants. You will know your plant has been overwatered if it is drooping but not wilting.

If your little seedling is in a large pot, the chances are good that you are going to have an overwatering problem. Seedlings don’t absorb very much water, and a large container requires lots of time to fully dry out. Instead of planting your seedling in a large container from the beginning, start it out in a smaller container until they have grown significantly. You can then transplant it to a larger container.

If you don’t have a choice any longer because the seedling is already growing in the large container, then you are going to need to adjust your watering method. Simply water the plant a small amount of water, and pour it over the seedling in a circle pattern. Makes sure the top inch of soil (up to your first knuckle) is totally dry before you water the next time. Don’t worry about water runoff with a small seedling until it has grown significantly. Your plants will actually grow faster if they are put in a smaller pot, so make sure you are choosing a pot that is the best size for them and then transplant as they increase in size.

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That being said, it is also not helpful to have a large seedling in a pot that is too small for it. This is more about the size of the root system than the size of the plant above the soil. Your seedling might become root bound (when the roots have wrapped themselves around the outside of the container, therefore not allowing water to escape through). Root bound plants often exhibit strange symptoms, including drooping and nutrient deficiencies, but also strange and unpredictable ones like interesting patterns of discoloration.

Often drainage (or, rather, a lack of drainage) is the problem when it comes to overwatering. If the water is unable to move freely through the soil and out the bottom of the container, you will run into overwatering health problems. Soil that is clay-based will not allow water to move freely through it, so avoid this type of soil when choosing your planting mix. You should also make sure that there are enough drainage holes at the bottom of whatever container you are using, and that these drainage holes are not jammed or clogged and therefore preventing proper drainage.

Perhaps the simplest cause of overwatering to fix is watering too frequently. You need to allow the soil to have enough time to dry, so as to give your roots an adequate and consistent amount of oxygen. Oxygen in water is absorbed rapidly by the roots, meaning they will also need to have pockets of air within the soil to survive. If you choose a lighter, more airy amendment for your potting mix (such as Perlite), it will retain more oxygen than a thicker or heavier soil. You can add as much as thirty to forty percent Perlite to the mix to ensure maximum oxygen retention.

Another way to increase the amount of oxygen in your soil is to use containers that allow air to come in through the sides as well as the top. Smart Pots or Air Pots are examples of such containers. Another way to combat overwatering issues is simply to water your plants less than normal during colder periods of temperatures. Their growth, processes, and water intake all slow down at lower temperatures, so don’t forget to adjust accordingly.

Underwatering seedlings

Seedling Underwatered – Image Powered by growweedeasy.com

Symptoms of underwatering include wilting, improper growth, and a lack of moisture in the soil. Although it happens less often than overwatering, it is still a serious problem that could negatively impact your seedling. It happens especially with beginners who have been warned – ‘never overwater your plants,’ so they overcompensate in the opposite direction.

If you combine underwatering with an overdose of nutrients, it will cause the seedlings to turn dark green, stunted, twisted, and new growth will be discolored.

Because there is a constant water loss in plants’ leaves through the transpiration process, they need to always have some presence of moisture to ensure proper functions and processes. If the roots can’t absorb any water, the plant processes will simply stop, and the growth will be significantly slowed or stopped. If roots are ever allowed to fully dry out, they will actually begin to die.

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While it’s a less common problem than overwatering, underwatering can be far more serious when it comes to negative health effects. If you look at the soil and you see that it has begun to separate from the container, this means that it is far too dry to be healthy for your plant. Underwatering is an especially grievous offense when it is combined with an overdose of nutrients.

If this has happened to your plants, it is at least a simple fix: just add more water. Start watering them more regularly, and they should start to bounce back quickly and relatively easily. Even if the soil mix is “hot” (which means that lots of nutrients have been added), your plant should have a good chance of adapting to it with an adequate supply of water.

Nutrient problems

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You will recognize nutrient problems in your seedlings if their leaves are yellow, crispy, spotted, or have other forms of discoloration. Your marijuana seedlings should be green at all times – it’s as simple as that. The nutrient problems might come from too many nutrients, too little nutrients, the wrong kind of nutrients, or something else.

If your plant exhibits symptoms like tip burn and dark leaves, it probably has a nutrient toxicity of some sort. After a while of an untreated nutrient toxicity, you will start to see other symptoms, such as yellow lines located on the seedling’s lower leaves.

If your plant has a nutrient deficiency, then its leaves will probably look pale or yellowing, and you might also see signs of other leaf discoloration. A nitrogen deficiency is almost always at fault, and this will make the leaves include brown with the yellow, and will go soft and will fold before they become crispy and drop off the plant. Don’t be deceived if the yellowing leaves are actually located at the top (newer growth only) – if this is the case, then it is unlikely that nitrogen is the nutrient at fault. A nitrogen deficiency generally affects the oldest leaves at the bottom of the plant before it reaches the other leaves elsewhere.

Problems with bugs can resemble nutrient deficiencies at first, so be careful to identify the symptoms correctly.

Your seedling’s nutrient problems might come from a “hot” potting mix, meaning it has lots of nutrients in it. This can simply be solved with adequate watering and waiting until the seedling has “grown out of it.”

If your soil is slow release soil, such as Miracle-Gro soil, it can cause nutrient burn and will eventually damage your final yield and bud development in the flowering phase. Don’t ever use a slow release soil.

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Seedlings don’t need many nutrients, so don’t overload them with them. As long as you have started with a high-quality potting mix, you shouldn’t add more nutrients until at least after the first few weeks of growth.

A nutrient toxicity can develop very quickly (within one night!) if you dump your plants with lots of nutrients all at the same time. When starting to feed your seedling nutrients, you should always use just half of what is recommended on the provided nutrient schedule. Check how your seedlings are reacting to it, and then you can increase the dose from there.

If your seedlings have a nutrient deficiency, it is most likely that a nitrogen deficiency is to blame. A nutrient deficiency of any kind could come from using a soilless medium that doesn’t have any added hydro nutrients, which are necessary for a hydroponic growing system. Another cause in a soil-based growing system could be that the grower isn’t adding in nutrients when the plant has used up the soil. Nutrients in soil don’t just sit there forever; they are absorbed and used by the plant, meaning you will always need to add in some more as time goes on.

One of the most common causes of a nutrient deficiency is feeding your seedling or plant the wrong type of nutrients. You need to make sure the right type of mix and use the right mix during the correct stage of life. Use a vegetative formula for your plant’s beginning part of life, and a “bloom” formula for the flowering and budding stage.

Once the plant is fully grown you will need to start thinking about flowering and harvest time. Our free little Harvest Guide will help you determine the best moment to cut your plants.

Another common nutrient problem with marijuana plants is a pH imbalance. Make sure to always maintain a balanced pH level, and you should be aware of the fact that the pH level will fluctuate. Improper watering (see above) will also cause a nutrient deficiency if left too long. Planting your seedlings in a container that is too small will lead to them becoming root bound, which will cause your seedlings to display symptoms of nutrient deficiencies. Problems with bugs can resemble nutrient deficiencies at first, so be careful to identify the symptoms correctly.

High temperatures

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If your plant is experiencing too high of a temperature, the leaves will start curling at the edges until they look like tacos or canoes. They will also wilt and start showing spots.

Make sure to keep a constant eye on the temperature of your grow room, or know the weather to see if you will need to install any special equipment to keep the air temperature of your plants down. Seedlings are happiest when the temperature is somewhere between 68 degrees and 77 degrees Fahrenheit. Make sure to use your own thermometer to double check this. You should also be sure not to position your grow room lights too close to your plants, so you can avoid burning on the closest parts of the plants.

Improper lighting

Burnt leaves, crinkled leaves, tall seedlings that are falling over, and lots of stem spaces between nodes are all symptoms of too much or too little lighting. Plants that are too tall have experienced too little light while plants that look burnt or fried have had too much light.

Whether it’s too much or too little, improper lighting can cause some serious problems for your marijuana seedlings. Luckily, it’s usually an easy fix: just move the lamps closer to or further away from your plants. If you are growing your plants outdoors, try covering them up on extremely hot days, and make sure every bit of your plant is exposed to direct sunlight. If they are exhibiting signs of lighting problems, you can fix the problem early on by adjusting the lights, and this should be enough to get your seedling back on their “feet.”

TIP: Looking to buy seeds? Visit the ILGM marijuana seed shop

Marijuana plant symptoms

Leaf symptoms:
– Discoloration
– Yellowing
– Crispy texture
– Spotted
– Tip burn
– Burnt edges
– Pale leaves
– Death of leaves
– Slowed growth

Plant symptoms:
– Wilting
– Drooping
– Algae growth
– Improper growth
– Slowed growth
– Dark green
– Stunted growth
– Twisted growth
– Discolored new growth
– Other discoloration

In general, your seedlings are going to want a moist environment, warm temperatures, and some light. They aren’t going to want much for nutrients. As long as you follow these points, your seedlings should be perfectly happy and healthy.

Remember that plants with strong genetics have less change of getting sick and are less vulnerable for diseases, deficiency’s, pest and environmental stresses. So make sure to buy marijuana seeds from a trusted seed bank.

Thanks for reading. Please leave comments or questions below and don’t forget to download my free grow bible


The founder of I Love Growing Marijuana, Robert Bergman, is a marijuana growing expert that enjoys sharing his knowledge with the world. He combines years of experience, ranging from small-scale grows to massive operations, with a passion for growing. His articles include tutorials on growing…

Cucumber Leaves Turning Yellow: The Facts and the Fixes

Chlorophyll and Chlorosis

Officially, your cucumbers’ distressing condition is chlorosis, or a lack of chlorophyll — the green leaf pigment responsible for capturing sunlight to fuel food production. Without enough chlorophyll, the plants go hungry — sometimes to the point of starving. To accurately pinpoint why chlorosis is happening, however, you need to study your cukes for other clues.

Pests and Yellowing Cuke Leaves

Infestation by a trio of sap-stealing pests leads to chlorotic cuke leaves. Fortunately, each causes other symptoms:

  • If your cukes have yellow-stippled leaves with fine silvery webbing draped from their underside, microscopic spider mites are at work.
  • If your cukes have malformed yellow leaves that curl under at the edges, suspect aphids. They mass on the stems and leaf backs and love to feast on new growth. Aphids also cover their feeding sites with clear, gooey honeydew.
  • If a cloud of miniature white moths rises from the yellow leaves when you shake them, you’re looking at whiteflies. Just like aphids, they excrete honeydew.

For organic control of these bugs, treat your cucumbers with insecticidal soap. Spray until it drips from all their surfaces and reapply at the label’s recommended frequency.

Expert gardener’s tip: Cukes severely infested with whiteflies should be removed and disposed of in sealed bags.

Disease and Yellowing Cuke Leaves

Diseases often blemish cucumbers with yellow spots and/or streaks.

Downy Mold

Leaves infected with downy mold develop yellow spots on their upper surfaces and grayish mold underneath. Cool conditions and splashing water encourage the disease. Organic control measures include:

  • Trellising your plants to improve air flow.
  • Watering them from beneath the leaves remain dry.
  • Spraying infected plants to runoff with a mixture of 1 teaspoon (4.9 ml) each of baking soda and horticultural oil in 1 quart (.96 liter) of water. Be sure to hit the backs of the leaves.

Fusarium Wilt

Fusarium wilt turns a cuke’s older leaves yellow from the edges inward as its runners slowly die. It’s spread by cucumber beetle larvae feeding on roots. Remove the infected plants and plant debris. To limit future outbreaks, protect your plants with lightweight row covers. Their permeable fabric keeps beetles away but allows light, moisture and air in.

Anthracnose Leaf Spot

An anthracnose infection begins with water-soak leaf spots that turn yellow and then brown. Anthracnose spreads in warm, wet conditions. Remove and destroy affected cukes. To prevent outbreaks allow plenty of space between your plants, prune excessive leaves and weed frequently.

Cucumber Mosaic Virus

CMV causes wrinkled, downward-curling leaves mottled with yellow spots. Affected plants seldom produce many runners, flowers or cukes. Because aphids spread the virus as they feed, it’s not unusual for an entire cuke patch to get infected. The only treatment is to remove and replace the plants.

In the best conditions, cucumber roots absorb more than a dozen minerals from he soil. When some are lacking, chlorosis results:

  • Nitrogen deficiency: Older leaves turn yellow on the tips and along the center veins while new ones remain green. Boost nitrogen by working a 2-inch layer of organic compost into the soil.
  • Iron deficiency: New leaves are solid yellow with small green veins while older ones remain green. Do a soil pH test and amend it appropriately to get the pH below 7.
  • Potassium deficiency: Leaves turn yellow at their edges and tips. Burying citrus rinds around the affected plants boosts potassium
  • Zinc deficiency: Leaves turn yellow between the veins. Spray them with organic kelp.

Overwatered cukes have yellow, wilted leaves due to oxygen-deprived roots. Rainfall included, cukes need just 1 to 2 inches of water per week. Don’t give them more. If your soil’s drainage is the problem, loosen it with sand or move the cukes to raised beds.

Inadequate Sunlight

Yellow, droopy leaves are a sign of cukes short on sunlight. Move them to a location with at least six hours of daily sun.

When Plant Leaves Turn Yellow

Healthy plant leaves are bright green in color. When plant leaves turn yellow, that means something is wrong. And it’s up to you to find that out!

The primary reason why healthy leaves are green is the presence of a pigment called chlorophyll. I won’t go into that discussion here, but a simple analogy for this is the same for humans. When you see a person who looks pale or red / flustered, you know something is wrong with them. That holds true for plants, too. Something is going inside the plant that makes their leaves turn yellow.

Plants can’t speak nor have facial expressions for us to know if there is something wrong with them. There are some instances where these leaves turn to yellow. This is an early sign that something is wrong with your plant.

If that happens, don’t panic. Here are 3 things you should check in that specific order to make them healthy again.

3 Easy Steps When Your Plant Leaves Turn Yellow

Underwatering and overwatering are both harmful to your plants. This is the first thing you should check when you notice that your plant leaves are turning yellow.

While there are some new technologies being developed about knowing when to water your plant, it is something a bit out of reach for most of us in terms of budget and geographic barrier (being developed in US and UK).

So, we do the next best thing — what farmers and our growers do — monitor how much water you’re giving your plant. Test this out a couple of times.

As we mentioned before, water your plants twice a day: early morning and late afternoon. If you want to be more specific, early morning is 7-10am; while late afternoon is 3-5pm. And there’s also a reason for that!

As for the right amount of water, the way to check that is to stick your finger in the soil about an inch deep. Don’t do that near the roots and / or stems. Do it around the edge of your pot.

  • If you feel it damp and moist, that’s perfect.
  • If you feel it dry and loose, you need to add more water.
  • When you pull out your finger and it’s like covered in chocolate, you overwatered it.

Do this for a couple of days. If the leaves didn’t turn back to its bright, green color, it’s time to move to the next item.

2) Make sure they are getting enough sunlight

Sunlight is a requirement for plants to perform photosynthesis. As a reminder, “Photosynthesis is process by which plants, some bacteria and some protistans use the energy from sunlight to produce glucose from carbon dioxide and water.” (source)

For those of us who forgot what photosynthesis is and the role of chlorophyll and water in the process, here’s another short explanation:

For plants to perform photosynthesis they require light energy from the sun, water and carbon dioxide. Water is absorbed from the soil into the cells of root hairs. The water passes from the root system to the xylem vessels in the stem until it reaches the leaves. Carbon dioxide is absorbed from the atmosphere through pores in the leaves called stomata. The leaves also contain chloroplasts which hold chlorophyll. The sun’s energy is captured by the chlorophyll.

In other words, photosynthesis is a process that transforms sunlight (and other components) into the plant’s food.

If your plant isn’t getting enough sunlight, that means it can’t convert the other components into food for its nourishment. This can cause the plant’s leaves to turn yellow.

Do this for a couple of days while keeping in mind the proper watering process. If it still has not turned back to green, then your plant might be malnourished.

3) Ensure the plant receives proper nutrition

We really cannot deviate from the human analogy. When a person is malnourished — both undernourished and overnourished — it is unhealthy.

The same goes for plants. If you add too much fertilizer, it can cause burns to the leaves; turning the leaves to brown. If you don’t add enough fertilizer, it can cause the leaves to turn yellow.

One note on fetilizers: not all fertilizers are created equal.

If you use our organic fertilizers, you generally just need to add 3-5 pellets every 14 days. Crush them, then sprinkle them around the plant before watering.

If you went through this process and checked that you are watering your plants properly and receiving the right exposure to sun, your plants will definitely go back to being healthy.

And if it doesn’t do let us know. There might be something else that’s causing the problem like bacteria problems, PH and chemical issues in the soil, temperature, etc. But these aren’t as common as the ones we mentioned above.

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