Why Is My Tomato Plant Turning Yellow?

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Everyone loves fresh tomatoes. They’re yummy, beautiful, and easy to grow. If you are wondering ‘why is my tomato plant turning yellow?’ then you’ve come to the right place. Today we’ll tell you the most common reasons that this can occur and what you can do to get your tomato plants healthy again in a jiffy!

Let’s talk about tomatoes and what they need to thrive!

First things first – the basics!

Starting off, you need to make sure that your tomatoes are getting a nice, balanced fertilizer. While you can certainly grow them without it, there are nutrients that your plant needs that might not be readily available in your garden. With yellow leaves, usually you’re dealing with a nitrogen deficiency, but that’s not always the case.

Iron and magnesium deficiency are another common cause when you’ve got yellowing tomato leaves, but thankfully there are good fertilizers for their stages of growth that can help. Once they’re juvenile they don’t need much help as seeds, as Nature provides, so a little bone meal of a 3-15-0 fertilizer is good. 

Once your tomatoes are flowering, however, you can switch to a 6-24-24 of an 8-32-16. This should ensure proper nutrition without overdoing it. Once your tomatoes are fruiting, however, then you should switch to an 18-18-21 – that’s because during this phase, they need a lot of nitrogen and phosphorus to really do their best. 

Types of yellowing to look for:

Here are some types of leaf yellowing to look for to help you to narrow the issue down more specifically:

Outer edges of the leaves are yellow and browning

If your tomato plants don’t have enough potassium then the leaves will turn yellow and then get brown around the edges.  

Yellow leaves and green veins

When your tomatoes’ leaves look yellow, but have green veins, then this is usually  a sign that they aren’t getting enough magnesium. You can treat this with a solution of Epsom salts – two tablespoons in one gallon of water. Use this to spray your tomatoes and magnesium is the issue, then you should see improvement within a week. 

The entire leaf has turned yellow

When you see completely yellowed tomato leaves, it’s usually a problem with nitrogen deficiency. Too much will get you a ‘bushier’ tomato plant that doesn’t bear as much fruit, but if yellow leaves mean that it needs more. 

Newer leaves look yellow

If the smaller, newer leaves on your tomato are the ones showing signs of yellowing, rather than your older leaves, then this may be a sign of calcium deficiency. Crushed eggshells can help with this in a pinch.

Disease 

Tomato plant in late blight
Tomato plant in late blight

Aside from nutrient deficiency, disease can also cause yellowing, with common examples including:

  • Tomato pith necrosis
  • Late blight
  • Southern Blight
  • Leaf molds
  • Buckeye rot
  • Fusarium wilt

Thankfully, You can avoid a lot of the fungal conditions with good watering habits, so that’s one problem out of the way. Using a hose, you can water at the base of the plant, or you can use drip irrigation. This will help to get your plant the water it needs, without getting the plant itself too moist. Your tomatoes will also need a lot of water – about 1 or 2 inches weekly, in most cases, but it depends on your local soil. 

Fungal conditions can really hurt your tomatoes, but if you’re careful to avoid too much moisture, that will definitely reduce the chances of this. 

Pest resistant tomatoes

You can also raise pest-resistant varieties of tomatoes and that will make a lot of your work much easier! There are many varieties that have been specially engineered to be resistant to disease. The next time you’re at the nursery, when you are taking a look at seeds, look for some of these identifiers:

  • V – Verticillium wilt resistant
  • F- Fusarium wilt resistant
  • FF – Fusarium Wilt types 1 and 2

These are just a few examples to give you an idea what to look for, but pest resistant tomato plants will definitely save you a lot of headaches. 

If you’ve got a good fertilizer and you’re still seeing yellowing leaves, there are a few additional strategies that you might try. For instance, with tomatoes, crop rotation is a good idea, as this can reduce the chance of diseases that can end up in the soil. You also shouldn’t grow them with potatoes or eggplants – these plants won’t get along well in your garden!

Pruning your tomatoes, as it turns out, can also improve your yields. Prune lower branches, as these are closest to the soil and the most disease prone, and you’ll see healthier tomatoes for your troubles. Just be sure to disinfect your gardening tools regularly so that if any of your plants are exposed to disease, you won’t be spreading it through the garden.

Watch out for herbicides

Tomatoes are sensitive to herbicides and so you have to be careful using them nearby. You can get creative with a lot of natural options to good effect. For instance, sprays with hydrogen peroxide and pepper can work quite effectively for dealing with mites and other pests. 

Companion plants

Another good way to ensure that your tomatoes are doing their best, is a little bit of companion planting. One good option is Marigolds – they’ll really brighten up your garden, but they’ll also help to keep aphids and mites at bay.

Planting garlic nearby can also help to get rid of soil-based pests and even zing up the flavor of your tomatoes. 

What if my tomatoes still have yellow leaves?

If you’ve carefully picked your fertilizer and you’re taking good care of your tomatoes, then it’s likely going to be a problem with disease. While we’ve listed a few examples, tomatoes are vulnerable to a large range of diseases, each with their own specific treatments. 

With fusarium wilt, for instance, all you can do is deal with the infected plants by removing them to stop the spread, but with problems like mildew you can fight the spread with sulfur dust and good pruning habits – it will all be a matter of isolating the particular disease.

FAQs

It’s just about time to wrap things up, but before we close for the day we’ve got some frequently asked questions to help fill in any gaps we may have missed along the way. Let’s take a look!

Does overwatering tomatoes cause yellow leaves?

Yes, overwatering or underwatering can get you yellow leaves on your tomatoes. A good rule of thumb is that you should give them about 1 inch of water a week if they are planted in a loamy soil, while sandier soils will be better with closer to 2 inches of water.

Should I remove yellow leaves from tomato plants?

If it just looks yellowed, rather than burnt or browning, then you can remove the leaf from your tomato plant. If it’s simply yellowed, however, then you might be dealing with a nutrition deficiency that can be quickly managed. 

Can you save a yellowing tomato plant?

In many cases, you can still save a yellowing tomato plant. In most instances, it’s a matter of the plant not getting enough nutrients, and testing is also a good idea – the pH needs to be close to 6.5 for happy tomatoes and if the soil is too acidic, it can affect nutrient absorption.

Some closing words

In today’s article we’ve answered the question ‘why is my tomato plant turning yellow’ and as you can see, it all depends on the ‘type’ of yellow. Yellow with green veins, for instance, means a magnesium problem is likely, while too little nitrogen will get you yellow leaves. Barring a nutritional deficiency, it could be a disease, but don’t panic just yet! Start with checking the basics -especially your plant’s fertilizer– and you’ll be surprised how big a difference a few tweaks can make!

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