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What Makes Tomato Leaves Turn Yellow? 

It’s no secret that growing tomatoes can be quite a daunting task, especially for inexperienced gardeners. Yellowing of tomato plants can be a huge cause of alarm since there are chances that it might arise from a myriad of issues. Whether you want to grow tomato plants using seeds on a nursery bed, or looking to source cuttings for propagation, you want to have insights on issues that might cause the leaves to turn from green to yellow.

What makes tomato leaves turn yellow

Right from the onset, having the right set of tips when watching out for early signs will draw you inches closer to formidable ways of diagnosing issues that cause the yellowing of the leaves. Some of the reasons that cause the leaves to turn yellow are trivial but can cause severe damage to the plant’s overall yield. In this guide, we’ve gone deeper to give you solid context whether you’re experienced or a starter, on the things to look out for in a bid to suppress the yellowing of leaves on your tomato plants. So, let’s get down to it.

Reasons for Yellowing of Leaves on Tomato Plants

While several issues could make the leaves of your tomato plants turn yellow, the most gratifying part is these conditions can be treated using tried and tested remedies. Yellowing of leaves doesn’t necessarily mean that you’ll eventually lose your entire tomato plant, so there’s no need to panic. There are dominant causes such as nitrogen deficiency, lack of enough sunlight, overwatering, or under watering. Even though you could take a wild guess and diagnose your tomato plants for these conditions, there are chances they could be suffering from other underlying issues. Let’s have a look at some other possible causes that you want to keep a close eye on.  

1# Transplant shock

Most tomato gardeners do not realize that transplanting can be a cause of the yellowing of tomato plant leaves until it’s too late. It’s often needful to note that when the time for transplanting checks in, especially during spring, most tomato plants go through an adjustment period that can often be the cause of the yellowing of the leaves. And one of the probable causes for mutation could be that the first few nights will be a bit frosty. 

During these first few weeks, it’s normal to see the dense color of the older leaves becoming lighter, while new ones will tend to appear more vibrant and radiant. Once the adjustment period is over, the tomato plants will go back to normalcy and the yellow leaves will eventually get replaced with lush green leaves. So, what’s the remedy for transplant shock? Right under the routine maintenance schedule, you want to spare some time for plucking off the yellow leaves. Cut them right from the stem part to give room for more vibrant leaves during the spring season. Yellow leaves often act as a breeding spot for intolerable diseases, so it’s best to entirely get rid of them.

And most of all, the right way to go about growing tomato plants and preventing transplant shock is to find out the variety that matches the growing conditions in your region. It’s also worth noting that some varieties happen to be more prone to transplant shock than others. So the mutation process can sail through with ease, it’s best to transplant your tomato plants during the night when the temperatures are lower. 

2# Early blight 

By far, early blight is one of the major causes of the yellowing of tomato leaves. It’s caused by Alternaria solani, a fungal pathogen that spreads through irrigation and insects. Early blight also travels from the soil to the plant and can cause major damage to the older leaves which eventually shrivel. At the onset, the fungus attacks the plant making it appear like there are halo-like spots on the plant which later begin to turn yellow and spread wide. As days pass by, the yellowing of the plant becomes more visible and invasive. If the condition is left untreated, leaves can turn brown then die off.

How to Fight Early Blight

So, what can gardeners do to help? Same as the lasting remedy for transplant shock, make sure to pluck off the severely affected leaves. Gardeners need to be cognizant of the fact that the longer you stay without cutting them off the faster the disease can spread to other healthier leaves or tomato plants. Another enduring remedy for preventing the disease from spreading is having spaces between the tomato plants. To keep early blight at bay, you need to give your tomato plants enough space for air circulation. Mulching will also help regulate the soil temperatures during the early weeks of spring when the nights are a bit cold. It also acts as a contact barrier between the leaves and soil.

Cut off any leaves that are touching the ground, regardless of whether they appear healthy or not. And that’s to limit the chances of getting into contact with the fungus that’s tucked in the soil. For tomato plants growing in the garden, drip irrigation would be the best watering method. And while you’re watering, be careful not to drench the leaves since if they’re soaking wet for longer periods, the fungus would find them quite much habitable. If you have to use overhead irrigation, ensure that you use it when the sun is bright at noon to ensure that the water evaporates quite fast from the leaves. After harvesting your tomatoes burn any residue and rotate and consider crop rotation during the next season, to fight pests and weed pressure. 

3#  Septoria leaf spot

Septoria leaf spot is yet another destructive fungal disease that rapidly takes a toll on the foliage of the tomato plants. On the face of it, newbie gardeners can mistake it for early blight as its symptoms are more or less the same. What strikes it apart from early blight is that the yellow spots are in mass numbers and take a circular shape. You might also spot a few lesions on the surface of the leaves. Consequently, if you don’t act promptly,  the leaves will turn darker then die off. Since this too is a fungal disease, you can make the best use of remedies for getting rid of early blight. And if the infestation is gruesome, spray your tomatoes with a soluble copper-based fungicide.

4# Verticillium Wilt

Verticillium wilt is one of the most common fungi that’s likely to affect tomatoes during a growing season. It emanates from the soil and in most instances, it has no cure so whenever it takes root on your tomato plants you would have no option but to uproot them. Sadly, there’s no chemical or organic remedy for this condition. While the disease is referred to as wilt, the leaves won’t show any signs of wilting until the plant hits maturity.

One early sign to show that your tomato plants are struggling with verticillium wilt is yellow-brown splotches that often appear on the lower side of the leaves, especially close to the veins. The condition will reach full-blown once the leaves begin to have bull’s-eye rot. To protect your tomato plants from verticillium wilt, use seeds or propagate them from mother varieties that are disease resistant. Aside from crop rotation, you also want to practice soil solarization before planting since the spores of this particular fungus stick around for quite a while. 

5# Fusarium Wilt 

Fusarium wilt appears at the tail end of the growing season when the tomato fruit has grown and matured. Your tomato plants are more likely to experience stunted growth during the growing season when the infestation hits record high. Infected seeds or soil could be a probable cause. And it’s no reason why most adept gardeners opt to sterilize shovels and other equipment before use. The most ideal conditions for harboring this disease include warm temperatures, dry surroundings, and an acidic soil pH ranging anywhere between 5-5.6. While you would find some tomato varieties that are resistant to fusarium wilt, they could still be susceptible to the disease if they’re infested with root-knot nematodes. 

As the name of this condition suggests, the leaves will wilt right from the shoot at the tip of the plant. During the elementary stage, the signs might be visible only on a single leaf that can recover during the night when the temperatures are cooler. Over time, the edges of lower leaves will begin to turn yellow. Leaves that appear overly-wilted will fall from the plant. Discolored stems also often indicate that your tomato plants could be suffering from fusarium wilt. And if you split the stems in half length-wise, you would see some dark brown scales. Even though using seeds that are resistant to this disease seems like a solid quick fix, a high population of nematodes in the soil will lower the resistance level. 

6# Tomato Pests

While some insects are biologically beneficial, you also want to watch out for pests that are leeching off of the yield. Pest attacks are fairly easy to identify. Tomato hornworms and psyllid insects are some of the common pests that feed on tomato leaves. Check for nymphs on the underside of leaves to ascertain whether your tomato plants are infested with psyllid insects.  Other pests to watch out for include aphids, spider mites, whiteflies, and flea beetles. Since cutworms and hornworms are visible, you can get rid of them by hand. 

7# Nutrient Deficiency

When it comes to nutrients composition, what makes the leaves of tomato plants green and in good shape is enough nitrogen supply. You want to check this essential element in the soil if the leaves begin to turn yellow. On the other hand, you want to be careful not to add excess nitrogen as it would scorch the entire plant. Excess nitrogen could also make your plants not yield any fruits. 

8# Excess Heat

Some refer to the effects of heat on tomato plants as ‘solar yellowing’ while others casually label it ‘yellow shoulders’.Solar yellowing often happens when the fruit production is about to ripen, accompanied by a steep rise in surrounding temperatures. Anything above 30 degrees Celsius would cause the leaves to turn yellow, especially if your tomato plants are growing in a garden without any partial shade. If there aren’t enough leaves to protect your tomato plants from intense heat, then they would likely suffer from solar yellowing.

On most occasions, leaves hit by this viral will curl upwards. It’s inversely worth noting that tomato plants are overly sensitive to freezing temperatures, so you want to strike a balance to prevent the leaves from thickening. There’s, however, no cause for alarm since this is just a temporary reaction to new environmental changes and doesn’t pose any dismaying effects on the production of fruits. Once the cold period is over, new foliage will develop.

Tomato Leaves Turn Yellow

Remedies for Protecting Tomato Leaves from Turning Yellow

Although we’ve highlighted a few tips you could work with to prevent the leaves of your tomato plants from turning yellow, it’s best if we shed more light on solid steps you can take to keep this from happening. First, you want to combat pests and diseases at all reasonable costs. Always make sure to inspect the leaves for any dark sport or signs of yellowing. Another tip that slips the minds of most newbie gardeners is the effects of excess watering. If you overdo this routine exercise, you’ll wash away calcium—an essential mineral responsible for the growth of cells and conductive tissues on tomato plants. You, therefore, want to avoid overwatering your tomato plant especially when the temperatures are below average.

Check whether the soil drains properly, has a neutral pH, and if the nutrients composition is at par with the typical needs of tomato plants. If the soil is too compact, you need to till it and add compost to boost its drainage capacity. Clay soil happens to be a bit hard, so amending it with organic material would make the soil less rigid. When digging the holes for planting your tomato plants, adding Epsom salt helps boost the photosynthesis process. You also want to avoid getting tempted to use excess fertilizer more so if it’s synthetic as it could cause the leaves to turn brown or yellow. Using organic fertilizers on tomatoes is highly recommended especially if you’re looking to keep the beneficial microorganisms alive. 

Final Thoughts on Tomato Plants Turning Yellow

It’s not strange to see leaves of tomato plants turning yellow whether you’re growing them in-ground, on a patio, or on the balcony of your apartment. In case you begin to see signs of yellowing, tips on this guide will help you navigate the muddling conditions. No matter the scale of your tomato garden, you want to be watchful for early signs at all times. And if you found this information useful, don’t miss sharing and drop a few lines in the comment box below. 

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