You’ve worked all spring to grow your wonderful tomato plants, maybe even starting in the winter to sow seedlings and give them the best chance at producing fruit.
Then one day you look out in your garden and see all your plants leaves are turning yellow! This can be devastating after all the work you’ve done, but luckily there are some easy ways to address this issue once you know the cause.
One of the most common causes of tomato plant leaves turning yellow is improper watering. Over or underwatering your plants can inhibit the uptake of nutrients and even cause issues like rotting or disease. Nutrient deficiency, lack of sunlight, herbicide or fertilizer burn, and transplant shock are other potential causes.
Also check: How to Get Rid of Red Bugs on Tomato Plants?
10 Reasons Your Tomato Leaves Are Turning Yellow
In this article, we will break down the most common causes of yellow leaves on tomato plants and more importantly, how to fix them!
1. Lack of Nutrients
Lack of nutrients is a potential reason why tomato plant leaves might turn yellow. Without the right amount of nutrients, your plant can’t grow correctly and doesn’t have the energy to support the leaves it already has.
Nitrogen is a key nutrient for tomato plants, and if your plant is not receiving enough nitrogen it will slow in growth. At the same time, older leaves will begin to die and turn yellow, indicating that your plant is not happy.
Leaves may also turn yellow due to a condition called chlorosis. This occurs when macronutrients are missing that are essential for photosynthesis.
If your plant is not receiving enough magnesium, iron, sulphur, or zinc, it cannot sufficiently produce chlorophyll (the pigment that causes plants to be green). When this happens, leaves will turn yellow but often still have bright green veins.
How to fix
If you suspect that nutrient deficiency is the cause of your problems, you’ll want to conduct a soil test first. This is because different nutrients missing might call for different treatments.
A lack of nitrogen can usually be fixed by applying a general plant fertilizer. Micronutrients that are missing might need more specific treatment.
A lack of magnesium can be treated by dissolving Epsom salts in water and spraying it on the leaves and roots of the plant. Powdered or granular chelated iron can be bought and sprinkled into the soil to help with the lack of iron.
Lime sulphur is another additive that will help with a lack of micronutrients. Finally, zinc can be added to the soil by increasing the organic content, like compost or other organic matter.
After addressing any specific issues, regular application of a general fertilizer (or one specialized for tomatoes) will help prevent nutrient deficiency in the future.
2. Watering Issues
Both over and under-watering your tomato plants can cause yellow leaves. Overwatering is a common issue. When plants are outside and the soil is subjected to more heat and sun, gardeners may over-compensate and provide too much water to their plants. This can prevent the roots from receiving proper oxygen and essentially starves them.
Alternatively, under-watering your plants prevents them from taking up the nutrients they need from the soil. Roots will dry and shrivel, and so will the top part of your plant when it does not have enough water to maintain cell structure.
Older leaves will be the first to dry up, turn yellow, and fall off as your plant tries to slow the loss of water to live as long as possible.
How to fix
Maintaining a consistent, appropriate watering schedule is the best way to prevent and reverse these issues. If your plant has been overwatered, allow it to dry out for longer than usual before watering again.
If your plant has been underwatered, water your plant frequently in short watering sessions getting gradually longer, to avoid shocking your plant.
Moving forward, pay close attention to your plants before and after watering to avoid giving too much (or not enough).
Fewer, longer watering sessions allowing water to penetrate deeply into the soil is better for your roots than short, quick watering that occurs daily.
This is because roots grow where water is, so if the water is only in the top foot of the soil, roots will now develop properly and grow downwards.
Check the soil with your hands every few days and water only when the top inch or two is dry. Adjust your watering schedule as needed based on rain, sunny periods, and temperature extremes.
Diseases in plants might be intimidating to diagnose, but once you know what to look for (and what disease you are looking at) they can be easy to treat.
Early blight and Septoria leaf spot are two potential diseases turning your leaves yellow. Early blight will cause a pale-yellow spot on the leaf, slowly turning brown with yellow edges.
Septoria leaf spot causes overall yellowing of the leaf with many brown spots all over. If left untreated, both issues can spread and cause damage to the plant.
“Wilts” are also diseases that can cause yellowing leaves. There are a few different “wilt” diseases, that often start at the bottom of the plant and work their way upwards, making the plant appear dehydrated even if it isn’t.
How to fix
In general, diseases must be caught and addressed as soon as possible to avoid permanent damage and spreading to other plants in your garden.
Early blight and Septoria leaf spot can be treated by removing affected leaves and discarding them. Apply a general fungicide to the affected plant to prevent re-infection.
Unfortunately, if your plant is affected by a wilting disease there is no treatment to cure it. Remove the plant from your garden as soon as you know it is infected with a wilt disease and be sure to avoid contact with other plants as this is easily spread to other plants in your garden.
4. Transplant shock
Transplant shock refers to the stress a plant experiences after being planted in a new area. This can happen when seedlings are started inside and then planted outdoors without being properly transitioned.
Minor transplant shock will likely only affect some of the smaller, lower leaves on your plant. If the top of your plant is green, healthy, and growing, you likely don’t have to worry.
However, if your whole plant is wilting or the top leaves are turning yellow, it might be too stressed to adjust to its new location.
How to fix
The easiest way to fix transplant shock is to, well, prevent it from happening in the first place! When you are getting ready to plant your seedlings outside, take them out of your house or greenhouse for a few hours every day, to expose them to the heat, sun, and wind of the outdoors.
Start with an hour or two and gradually build up the time over the course of a week or so to allow them to adjust. This is called “hardening off” and will help your plants better adjust to the new conditions.
Once your tomatoes are planted, water them thoroughly and regularly to help roots establish. If your seedlings are being planted somewhere with lots of sun exposure, consider sheltering them from the sun with a light sheet until they are stronger.
You should also pay close attention to nighttime temperatures, as cold will damage your plants as well. Cover them with small containers or tents overnight to keep them warm.
5. Lack of sunlight
Not surprisingly, your plant will suffer if it isn’t getting enough sun. Tomato plants need a lot of sun to be happy, grow fast, produce fruit, and allow those fruit to ripen. Ideally, your plant will get full sun, which means sunlight directly on your plant for a minimum of 8 hours a day!
How to fix
If the tomato plants in your yard are potted, consider moving them. This might require moving them a few times a around your back, front, or side yard to ensure they get enough sunlight.
Set a reminder and stick with it, it’s worth it! If your plants are on a balcony or inside, consider getting a high-power grow light to help your plants get enough energy.
There are a wide variety of models available, from small lights for single plants to larger ones for many plants at a time.
If your plants are in the ground, your options are more limited. Consider why your plants are being shaded. Is there a tree next to them blocking the light? A patio awning or tent? Or maybe a fence blocks most of the sun.
To fix these issues, consider pruning or trimming back adjacent trees and shrubs to allow more sun to reach your plants. Move furniture and other structures out of the way if possible.
Pay close attention to where the sun in your yard falls and consider planting your tomatoes in another location next year to avoid this issue.
6. End of the season/frost
If there are plenty of fruit on your plant, or you’ve even harvested a few rounds of tomatoes already this summer, it’s possible it is just time for your plant to finish up for the year.
As fall approaches, your plant will slow in growth and older leaves will turn yellow and die off. This process will accelerate as nights get cooler and frost starts to damage the leaves.
If this is the case and you aren’t too concerned, you can simply allow your plant to finish its life cycle. If you still have a few fruit to ripen on the plant, trim off any new growth to allow the plant to focus on ripening the tomatoes it has, rather than growing new ones.
How to fix
There isn’t much you can do to reverse the natural progression of your plants life, but if you need to extend the growing season just a little longer to allow your fruit to finish growing, you can try a couple easy tricks.
If your tomato plants are in pots, simply move them inside or into a greenhouse for the last few weeks to slow this natural process and allow your fruit to ripen.
If your plants are in the ground, do not transplant them into pots, as this might stress the plant too much and cause you to lose all the fruit!
To protect outdoor plants from the changing seasons, cover them at night with a plant protector tent, usually a light frame made of wire and a thin, breathable fabric.
You could also gently drape thin sheets over your tomato cages at night, but make sure the fabric doesn’t touch too much of the plant as this might cause issues.
7. Young leaves/seed leaves falling off
Just like older leaves will turn yellow and fall off when their life cycle is done, young leaves of seedlings will do the same!
This is a natural process of the plants life, just like when kids lose “baby teeth” to grow new “adult” ones, your plant needs to shed its young seedling leaves to grow larger leaves.
These larger leaves will help your plant grow faster by taking in more sunlight, which is needed for photosynthesis.
How to fix
No fix needed for this one! If you don’t like the look of these small, yellowing leaves, simply pinch or trim them off and dispose of them.
8. Herbicide damage
Tomato plant leaves are sensitive to changes in their environment and susceptible to damage from herbicide drift.
If you have sprayed your lawn or driveway for weeds, it is possible that wind carried herbicide over to your garden, landing on leaves and causing damage.
This damage might appear as small yellow spots on leaves that gradually get larger, or whole plants dying for no noticeable reason.
How to fix
To avoid herbicide damage, stop using herbicides! Weeds in your lawn can be treated with natural alternatives to chemical sprays, like mixtures of vinegar, salt, and dish soap.
These mixtures can also be applied to driveways and walkways or pouring hot water on weeds will kill them as well.
If you must use herbicides, protect your garden plants by not spraying on windy days. You can also consider installing a windbreak or planting a hedge to stop the herbicide from drifting. This can also protect from herbicide drift from neighbours yards or adjacent farm fields.
9. Soil compaction
Soil compaction can cause issues like overwatering. When soil is too densely packed, roots have trouble “breathing” properly and struggle to pass oxygen, water, and nutrients to your plant.
As your plant slowly dies, leaves will begin to turn yellow which signals that something is wrong.
How to fix
To avoid compacting your soil, try not to walk directly over the root zone of your plants. This is about 1-2 meters on all sides of your plants, and the zone is larger the bigger the plant is.
Grow your tomatoes in raised planter beds or large pots to prevent this from happening, or fence off around your plants and don’t be tempted to step on the soil to water and weed!
Avoid planting tomatoes in soil with poor structure, and amend soil before planting, since doing after can cause damage to the roots.
Improve soil structure by adding in organic matter like compost or mulch that will break up dense soil clumps and allow proper aeration. Mulching on top of soil around your plants can also help to prevent compaction even more.
10. Fertilizer shock
Similar to herbicide damage, fertilizer shock can also cause yellowing leaves on plants. This happens when a plant receives too many nutrients in the form of a chemical fertilizer, which shocks the plant and causes a type of burn.
Leaf damage from this issue usually includes dry, crispy edges, yellowing or browning of the leaf, or leaves dropping off the plant completely.
How to fix
To fix fertilizer burn, be sure to water your plant thoroughly and allow the water to flush the fertilizer from the soil and roots. Remove any damaged part of the plant, using clean, sharp gardening shears to remove yellow leaves and stems.
Allow your plant to fully recover from the shock and water regularly for about a month following the stress. Wait a month or so until reapplying fertilizer to the soil around the plant and use half-strength until you are sure your plant won’t react poorly again.
Should I remove yellow leaves from tomato plant?
Except for disease that may spread to the rest of the plant, leaving yellow leaves on your tomato plant are not likely to cause any harm.
However, these leaves are not particularly attractive, and if you would rather not look at them there is also no harm in cutting them off!
Trim yellow leaves off properly by using clean, sharp, and sterile garden shears to cut as close to the stem of the plant as possible without causing additional damage.
Discard leaves and do not let them fall to the base of the plant to decompose, as this can encourage rot and disease to develop.
What are the signs of overwatered tomatoes?
Overwatered tomato plants will exhibit a few signs indicating that they are getting too much water. Leaves may be wilted, limp, and yellow, eventually falling off completely.
Leaves may also form small bumps or blisters caused by the retention of too much water. The base of the plant may be soft, brown and mushy rather than firm and green.
Digging deeper, you may find the same signs of root rot on your roots, which should be pale in colour and firm to the touch.
Can yellow leaves turn green again?
Yellow leaves are turning yellow because for whatever reason, the plant has decided it does not have the energy and resources to maintain those leaves.
By allowing them to turn yellow and die, the plant can direct energy towards new growth or maintaining more essential functions. This might be cause by disease, damage, or stress caused by the many reasons covered above.
Because of this, yellowing leaves are likely to continue to turn yellow and eventually die, falling off your plant.
However, if you know the cause of your leaves turning yellow you may be able to properly address these issues and stop any additional leaves from dying.s