Yellow leaves on tomato plants signal a problem.
Here’s how to figure out what’s going on.
Yellow leaves on tomato plants are a sign that there’s a problem.
Credit:vinhdav / Getty Images
The causes are variedincluding disease,pests, environment, and plant care.
But there is good news.
Yellow leaves on tomato plants can often be fixed (or at least managed).
vinhdav / Getty Images
1.
Transplant Shock
A few yellow leaves on tomato plants within a week or two oftransplanting the seedlingsis not uncommon.
Some slight yellowing is a common response.
What to do:Provide adequate water.Seedlings thrive in soil that is moist, but not wet.
They will establish an extensive root system within 4 weeks or so.
At that time, transition towatering plants deeplyonce or twice a week during dry periods.
Also, limit seedling stress by protecting young plants from cold temperatures.
If nighttime lows drop below 45F, cover plants with a bucket or box.
Uncover in the morning.
Nutrient Deficiency
Tomato plants grow fastand that growth requires plentiful nutrients.
The most common nutrient deficiency is nitrogen.
Iron deficiency or low magnesium levels are also common issues.
Early Blight
This frustrating fungal disease first shows up on the lower leaves of a plant.
Small brown lesions develop and soon the surrounding tissue turns yellow.
Early blight survives in the soil and splashes up onto the leaves during rain or when plants are watered.
What to do:Remove diseased tomato leaves and stems and dispose of them.
Minimize the spread of disease bycleaning your pruning shearsbetween cuts.
Prevention is key to avoiding early blight.
Do not water overhead.
Late blight is characterized by yellowing leaves with irregularly shaped brown lesions.
If this occurs, the diseased leaves will turn brown and quickly fall off the plant.
Spread by the wind and rain, late blight can move through a garden or neighborhood quickly.
Discourage late blight by planting seedlings 3 to 4 feet apart to encourage good air circulation.
This helps prevent late blight from taking hold by ensuring that foliage dries more quickly.
Inspect the leaves closely and youll see white powdery growth on the top and undersides of leaves.
What to do:Fungicides containing sulfur or copper can be effective.
Biological products are effective too.
Fungicides must be applied weekly to maintain control.
It most commonly occurs whentomato fruit begins to matureand may be visible on just one side of the plant.
Once fusarium wilt takes hold, the diseased leaves will wilt and the entire plant will eventually die.
What to do:Remove and destroy infected plants.
Salt Damage
Tomatoes growing in potsare especially susceptible to excess salt and other mineral buildup in the soil.
This will flush outexcess salts and minerals.
The rinse will also wash away valuable nutrients so be sure to fertilize tomatoes growing in containers regularly.
Leaves impacted by herbicides will quickly turn pale yellow, often mottled with white.
What to do:There is no remedy for a tomato hit by herbicide.
The best tactic is prevention.
Too Much or Too Little Water
Tomatoes generally need about 1 to 2 inches of water per week.
Too much water or too little water can cause leaves to turn yellow.
What to do:Avoid overwatering your tomato plant by checking the soil moisture before turning on the hose.
Sink your finger into the soil at the base of the plant.
Water when the soil feels dry to the touch 2 inches below the surface.
When watering tomatoes, a slow trickle over a longer period is better than a rapid splash.
This will encourage your plants to develop a deep root system that is more drought-resistant.
Those varieties are not completely immune to diseases but may fare better than othersespecially in favorable conditions.
Look for codes on the plant labels that indicate built-in resistance.
Some plants may have multiple indicators (e.g., VF stands for verticillium wilt and fusarium wilt).
The answer is not a clear yes or no.
Unblemished tomatoes from damaged plants are likely safe to eatjust be sure to wash them well.
However, diseased tomatoesespecially those showing signs of blightare not recommended for canning or freezing.
This is also true of frost-damaged tomatoes.
Tomatoes showing signs of herbicide damage should not be consumed.
