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There are several reasons why the leaves of tomato plants turn yellow.
However, new yellow leaves on tomato plants are more concerning.
Here is a list of possible causes and remedies.
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Watering should be done slowly and deeply so the plants form deep roots.
Avoid overhead watering and always water at the base of the plant.
Too Little Light
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Tomato leaves turn yellow if they are not getting enough sunlight.
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Tomato plants require at least six to eight hours of sunlight daily.
If you are growing your tomatoes in containers, move them to a sunnier location.
Prune trees and shrubs around garden plots to increase the direct sun exposure of the plants.
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Transplant shock may last up to two weeks.
Water the plants well during the four weeks after transplanting to help roots establish.
Protect the plants from temperatures below 45F and cover them during cold nights as needed.
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Container-grown tomato plants are more prone to fertilizer burn than in-ground plants.
Treat fertilizer burn by flushing the plant with water.
This is particularly effective with container-grown plants.
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Water thoroughly until the water drains from the drainage holes.
Read the fertilizer label carefully.
If you’re unsure aboutfertilizer quantity and frequency, it’s always better to under-fertilize.
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Nitrogen Deficiency
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Nitrogen deficiency is another possible reason for yellowing leaves.
Tomatoes are heavy feeders that require balanced fertilization.
Fertilize the plants with a tomato fertilizer.
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Use a liquid tomato fertilizer instead of a granular product for faster results.
The leaf veins may appear dark green, but the remaining leaf is pale.
The ideal pH level forgrowing tomatoesis between 6.2 and 6.8.
Iron deficiency is most common in sandier soils and soils with a high pH.
Conduct a soil test to check yoursoil pH.
Plants need magnesium to produce chlorophyll; otherwise, the leaf will not become green and vibrant.
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Use a fertilizer that contains micronutrients like iron and magnesium.
Yellow leaf curl virus is common in tomatoes and is transmitted bywhiteflies.
Symptoms include yellow leaf margins, upwardcurling of leaves, and stunted leaf growth.
Tomato spotted wilt virus is one of the many viruses that causes leaf curlMiyuki Satake / Getty Images
The disease can also cause flowers to drop, stunted growth, and poor fruit yield.
Deter whiteflies by using aluminum or silver-coated reflective mulches between planting rows.
Remove plants and bag them for disposal at the end of the growing season.
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They all present with yellowing leaves.
Fortunately, most are treatable using the same methods.
Most tomato leaf diseases overwinter in the soil and splash onto the plant’s lower leaves during watering.
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These diseases thrive in areas with high summer humidity.
To help control these problems, trim and dispose of infected lower leaves and branches.
Stake andprune tomato plantsto improve air circulation.
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If the disease worsens or is severe, use mancozeb fungicide, chlorothalonil, or copper fungicides.
Remove all plant material at the end of the season and rotate crops the next growing season.
Unfortunately, it is not possible to chemically control fungal wilt diseases.
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Remove and discard diseased plants.
Do not compost these plants, as the pathogens spread via compost.
Fusarium wilt is a warm-weather disease that can occur in seedlings.
The less common verticillium wilt does not affect seedlings and usually appears later in the season in cooler soils.
Tip
Nursery-grown tomato cultivars and seed packets may have the resistance letters VF on the plant tag.
Avoid using herbicides near your tomato crop and resort to hand-weeding instead.
If you use manure as a fertilizer or hay as mulch, they may be contaminated with residual herbicides.
Sunscald of the leaves is temporary and shouldn’t affect the plant’s overall health.
However, as sunscald usually occurs in extreme heat, keep your tomato plants well-watered during hot weather.
Here are some other helpful tips to prevent yellowing leaves.
Overwatering causes leaves and stems to droop or wilt.
The leaves wilt because the soil has more moisture than the roots can absorb.
Remove yellowed tomato leaves.
Yellowed leaves rarely turn green again.
Epsom salt can be used to help support a tomato plant that has a magnesium deficiency.
Kluepfel, Marjan, et al.Tomato Diseases & Disorders.
Home & Garden Information Center | Clemson University, South Carolina, 8 July 2021.
Egel, Daniel S.Vegetable Diseases: Five Steps for Healthy Garden Tomatoes.Purdue University Extension.
Possible Causes of Sudden Wilt and Death in Tomatoes.
Nebraska Extension in Lancaster County.
