Tomato seedlings turning yellow | 8 Reasons and easy solutions

Tomato seedlings will turn yellow if they are getting too much water which can wash away nutrients including nitrogen. Tomatoes need nitrogen for good leaf growth and to support photosynthesis. Yellow tomato leaves can be solved with liquid nitrogen fertilizer and reducing the amount of water that is given to the plant.

Plant yellowing tomato seedlings into a garden bed to help them grow larger.

Top reasons why tomato seedlings turn yellow

Too much water

Too much water can cause tomato seedlings to turn yellow as nutrients are washed away from the roots. To reduce the need to water so often, add a 2 inch layer of straw mulch under your tomato plants. This keeps soil moisture in and reduces the risk that nutrients will be washed away.

Give your tomatoes a quick feed of nitrogen rich fertilizer like liquid fish emulsion to replace the nutrients lost quickly. Place a slow release nitrogen fertilizer around the tomato seedling like pelleted chicken manure for longer lasting nutrients.

Not enough light

The bottom leaves on your tomato plant can turn yellow over time. This is not a problem and the leaves can be removed once they have turned brown.

Tomato seedlings that do not get enough light will turn yellow over time. Tomatoes light to photosynthesize which is where the green chlorophyll turns light and carbon dioxide into food for the plant. Without sunlight the leaves will turn from green to yellow and eventually the tomato plant will die.

Move indoor tomato seedlings out into the bright light when frosts have passed to fix yellow leaf problems from lack of sunlight. Plant tomato seedlings out into a sunny spot in your garden to encourage them to grow strong, healthy green leaves full of chlorophyll. This helps the plant to develop sugars which go into making the stem structures and leaves.

This tomato seedling has bright green leaves and was ready to plant into a raised garden bed after 4 weeks of growing from seed.

Not enough nutrients

Tomato seedlings that do not have enough nutrients, in particular nitrogen will turn yellow. Tomato seedlings need a range of nutrients to grow and absorb the nitrogen which will help to green their leaves. An organic pelleted chicken manure is a great slow release fertilizer containing a range of nutrients that will prevent tomato leaf yellowing.

Add a fruit promoting fertilizer before the flowers and tomatoes have grown. Add this in late spring for the best results and to encourage more flowers and fruit on your tomato plants.

First 2 tomato leaves will turn yellow

Tomato seedlings will grow two leaves first that are called cotyledons. Once the tomato seedling grows a second and third set of leaves, the smaller leaves will turn yellow. The tomato seedling will re-absorb the nutrients from the leaves, they will stop photosynthesizing and turn from green to yellow.

As the tomato plant grows, the bottom leaves can yellow and die off. These can be removed without harm to the plant. It is a good idea to remove them if they are touching the ground as this can encourage insects or fungus which can get on the leaves from the mulch or soil.

Next 2 tomato leaves turning yellow

The next two leaves after the cotyledons should stay green until the plant grows larger and if they turn yellow this is a sign that the plant is missing nitrogen, getting too much water or not enough sunlight. If the second set of tomato seedling leaves turn yellow, add a liquid nitrogen fertilizer, move them into brighter sunlight and only water when the surface soil becomes dry.

If tomato leaves turn yellow you have a problem with water, nutrients or light.

Tomato seedlings turning yellow – FAQ

Why are my tomato seedlings turning yellow?

Tomato seedlings turn yellow when they are not getting enough nitrogen which can be caused by overwatering which will wash nutrients away. Add a liquid nitrogen fertilizer for a quick nutrient boost. Move tomato seedlings into bright sunlight and if they are big enough, plant them out into your garden beds or raised containers or pots. Use good quality potting soil and surround them with straw mulch.

How do you fix yellow tomato seedlings?

Fix yellow tomato seedlings by planting them out into garden soil that has added aged cow manure, pelleted chicken manure and compost. Water the seedling in with organic liquid nitrogen fertilizer. Only water again when the soil is dry 2 inches below the surface.

What do overwatered tomato seedlings look like?

Overwatered seedlings will have yellowing second leaves and can start to droop over. If they continue to get too much water, they will eventually go brown and die. If you catch it early enough your seedlings can be saved. Add nitrogen and slow down your watering schedule.

Should I cut yellow leaves off tomato plant?

Do not cut off yellowing cotyledon leaves from tomato plants as they will reabsorb any nutrients in the leaves to strengthen the plant. The cotyledon leaves are the first 2 leaves the plant forms and they will eventually dry off and drop from the plant. They will cause no harm if left on.

Remove any larger yellowing leaves that may be touching the soil. This will reduce the risk of disease and insect attack.

How often should I water tomato seedlings?

Water tomato seedlings when the soil is dry 2 inches below the surface. Tomato seedlings like regular water over the warmer months and in the heat of summer May need watering everyday. For cooler regions with lots of rain, reduce watering to 2-3 times per week so that nutrients are not washed away and the plant does not end up with yellow leaves.

Tomato seedlings turning yellow – Summary

Tomato seedlings can turn yellow if they are getting too much water but the easy solution is to plant them out into your garden with lots of organic matter mixed into the soil. Tomato seedlings that are left in their pot for too long will not have enough nutrients in the seed raising mix they were grown in to keep going.

As soon as you get your tomato seedlings home, plant them out into your garden, making sure that there is no risk of frosts and they will grow happy and healthy and you can avoid yellow leaves.

Happy Planting.

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