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Why Are My Tomato Leaves Turning Brown? How To Keep Plants Healthy In The Summer!

As summer hits full stride and tomato season gets into full swing, many gardeners become alarmed when some of the leaves on their tomato plants begin turning brown – and in some cases – even begin to die and fall off.

This can be especially true for the lower leaves of tomato plants in mid to late summer. Quite often, when a plant has any issue at all – it will show up first on the lowest leaves. And if the issue is serious enough – it then spreads to the rest of the plant.

One thing is for sure, for tomato growers, the last thing they want is trouble with their plants after nurturing them all spring and early summer. Especially now that they have finally matured enough to start producing a harvest!

tomato leaves turning brown
One of the first sign a tomato plant may be in trouble are when its leaves begin to turn yellow or brown.
Why Are My Tomato Plant’s Leaves Turning Brown?

So what is the cause? Could it be a lack of water or nutrients? Maybe the start of the dreaded tomato blight or another tomato disease? Or could it be an invasion of pests trying to mount an attack on your plants?

The truth is, there can be a lot of reasons the leaves of a tomato plant starting to fail or fade in mid summer. As you will see below, late season blight is certainly a major culprit for the failure of many late season tomato plants. And in other cases – the plant dying back is completely natural.

So before you begin to think your tomato crop might be in serious jeopardy, here are a few important things to know about how your tomato plants grow in mid to late summer – and how those yellowing or browning leaves might not be the end of the road for your plants – or your tomato harvest!

Why Are My Tomato Leaves Turning Brown & Falling Off?

Determinate vs. Indeterminate Tomatoes

In some cases, the reason a tomato plant’s leaves may be yellowing and dying off can be 100 percent natural. Why would a tomato plant suddenly begin to die in the middle of summer? Because it may be a determinate tomato!

roma tomato
This determinate Roma tomato isn’t sick. It has merely reached full maturity and has completed its growth cycle.

Tomatoes are either determinate, or indeterminate. Indeterminate tomatoes will grow and produce until killed off by a frost or a freeze. But determinate varieties of tomatoes have a set life span. They produce their entire crop over a three to four week period, and then quickly die off.

A great example of this is with the Roma tomato. Roma tomatoes are quite popular among home gardeners. But Roma tomatoes are determinate plants. So after their main crop has ripened, they will die off – no matter what.

Unfortunately, this plant often is mistaken every year by gardeners as having a late season issue – when in reality, it has simply run its course. So before you think your plant may be in trouble, check to see if it might just be a determinate variety. See: Determinate and Indeterminate Tomatoes – How To Know The Difference, And Which To Grow!

If your plant is not a determinate and is starting to have yellowing or browning leaves – then it most likely one of these following issues:

Lack Of Nutrients – Why Are My Tomato Leaves Turning Brown?

One of the biggest reason tomato plants suffer in the summer is from a lack of nutrients. Tomato plants are heavy feeders. Because of that, they quickly can use up the available nutrients in the soil. And when they do, the leaves and the plant can begin to suffer.

Jacks Tomato feed
The best fertilizers for feeding tomatoes in the summer will have more phosphorous and potassium than nitrogen.

Summer fertilizing is vital to keep your plants strong, healthy and producing. Fertilize your plants every fourteen days with a liquid fertilizer that has more phosphorous and potassium than nitrogen. This will help it continue producing blooms and fruit, and not just green up the foliage. Product Affiliate Link: Jack’ Classic Tomato Feed Fertilizer

Lack Of Water – Why Are My Tomato Leaves Turning Brown?

Another big reason tomato plants suffer in mid summer is from either too much or too little water. Tomato plants need between 1 an 1.5 inches of rain weekly. If it is not falling from the sky, watering is vital to keep the foliage strong and the plant producing.

More than anything else, keep plants watered during extended dry periods. When watering, water deeply and not just for a few minutes at the surface. This will help the plant grow its roots deeper, protecting them from drying out easily.

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Avoid Fruit Overload

So what if you are growing indeterminate tomatoes and still having a problem with your plants not producing more and starting to look weak? In some cases, your plant might be suffering from fruit overload.

If you allow too many tomatoes on a plant at once, it will cause the plant to stop producing. This is called fruit overload and is common on not just tomato plants, but many vegetable plants.

Tomato plants should be harvested often in the growing season. This will keep the plant’s energy on growing and producing. And don’t worry if those tomatoes are not fully ripe. As it turns out, it is better to pick tomatoes as they barely start to turn and let them ripen off the vine! (See: When & How To Pick Tomatoes)

Late Season Blight – Why Are My Tomato Leaves Turning Brown?

Tomato blight is certainly a big issue for many tomato plants in late summer. Although blight can occur at any point in the growing season, it is most prevalent near the end of the growing season.

first signs of tomato blight
Once the tell-tale signs of blight show up, it is usually too late to help the afflicted plant. The real key to stopping tomato blight is prevention.

Tomato blight is a spore disease that infects the soil and plants. The spores can spread quickly via the wind, especially as plants grow larger late in the season. Although dying, browning foliage is a symptom, the real tell-tale sign of tomato blight is greasy, oily spots appearing on your tomatoes. When you see this, it is definitely time to pull the plants.

Tomato blight is highly contagious, and controlling it as quickly as possible is extremely important. Do not compost the plants, but instead burn or discard them. In addition, locate next year’s plant’s as far from the space as possible.

Here is to keeping your tomatoes producing this year – and to a great harvest right up until late fall. That is, of course, if you are not growing indeterminate tomatoes!

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