What Causes Tomato Blight? Garden Tips 2024

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Gardening can take a lot of work and the last thing you want is some external force derailing your plans. Tomato blight is a fungus and if not caught early, it can ruin your entire crop.

What causes tomato blight: Tomato blight lives in the soil and is a fungus that moves through the air. It will first attack the leaves of your tomato plants and depending on whether it is early season or late season blight, can then attack your tomatoes. While tomato blight is not toxic to humans, it can quickly destroy your tomatoes, leading them inedible. The best way to keep your tomatoes healthy is to prevent the spread of the fungus. Rotate your crops to keep the soil aerated, add mulch to prevent the fungus from moving from the soil to the air, and keep a close eye on your plants.

Why do my tomato plants get blight?

Tomato blight is a fungus that lives in the soil. It starts by attacking the stems and leaves of your tomatoes and can then move into your fruit.

As a fungus, tomato blight is airborne and can be transferred to your garden on the wind. While there is no way to stop it from entering your garden, there are, however, steps you can take to prevent your tomatoes from becoming infected.

Types of Tomato Blight

There are actually two types of tomato blight and they have to do with the timing of your plants.

Early Blight

Right when your tomatoes actually start growing, they can be infected with early blight. You may see the green leaves on your plants start to turn brown and then if the blight continues, the leaves will turn yellow, wither, and die.

If you see this happening, immediately remove the infected leaves on your tomato plant. Carefully dispose of them so that they can’t infect the rest of the plant.

Your tomatoes won’t be affected by early blight but a plant can’t grow if it doesn’t have any leaves, so any fruit will be doomed.

Late Blight

Unlike early blight, which can be remedied, late blight is much more fatal. With late blight, you may see signs of black markings on your tomato leaves and this quickly spreads to the rest of the plant, including the fruit.

Your tomatoes, which should be yellow to red at this time, can become inedible thanks to the blight. Unfortunately, all your hard work of growing is lost due to late blight.

How to Prevent Tomato Blight

Step 1 – Crop Rotation

The first, and best step to preventing tomato blight is to rotate your crops. This means you don’t simply plant your tomatoes in the same part of your garden as you have in previous years.

Remember that tomato blight lives in the soil and once it is established, it can live for multiple years. Even if your tomatoes don’t show signs one year, the fungus can simply be dormant and the following year can start to infect your plants.

Set up a system where you move your crops around your garden every year. This will keep the soil moving and won’t allow any fungus to take hold of new plants.

Step 2 – Take a soil break

Unfortunately, if you do have tomato blight, you need to stop using that part of your garden for tomatoes. No matter what you do, if the fungus is living in the soil, it can still be alive for up to five years.

The good news is that tomato blight won’t affect other plants so you can plant different crops in the affected area.

Step 3 – Mulch your garden

Adding mulch to your garden has so many benefits, including added nutrients and more moisture. Another benefit is that it can prevent tomato blight.

Because blight is a mold, it releases spores that are transported to plants. However, this transportation is actually done through the air and not through the soil.

So, even if you have the blight fungus in your soil, a layer of bark mulch will prevent it from becoming airborne.

Once you plant your tomatoes, add a thick layer, about 3 to 4 inches, of bark, straw, or leaf mulch. Not only will this help prevent blight but it will make your tomatoes much healthier.

Step 4 – Skip the compost

A compost bin is an essential part of any garden and it makes sense to put old plants in at the end of your growing season. However, it’s best not to compost your tomato plants.

Within those leaves and stems can be pests and diseases that won’t simply break down in your compost. Instead, they will lurk in the new soil and when you add it to the rest of your garden, you may inadvertently spread unwanted pests to the rest of your garden.

Even when you are trimming your tomato plants, put all clippings into your garbage instead of your compost.

What Does Tomato Blight Look Like?

Tomato blight can affect both the foliage of the tomatoes and the tomato fruit itself. Early blight only affects the foliage, which will turn brown and then yellow.

With late blight, black spots can appear on the foliage which then spreads to the fruit. The tomatoes that are still on the plant will have black markings and this can spread to the entire fruit.

Can you eat tomatoes with blight?

Eating tomatoes with blight is a personal preference. If you pick the tomatoes when they only have a small amount of blight, you can cut off that part and eat the rest.

Tomato blight is not toxic to humans, so you won’t get sick from it. However, blight can move quickly and your tomatoes may not be ready for harvest once they become infected.


Tomato blight is unfortunate but there are ways to prevent it. Rotate your crops, don’t compost your old tomato plants, and use a mulch to prevent the spread of the fungus. With a few simple steps, you can ensure the hard work you put into growing your tomatoes is not in vain.

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