Tomato Week

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Tomato Zippering: Why It Happens & How to Prevent It

Tomatoes are a staple garden plant in backyards and farms around the world, but they can come with several unique challenges. While they aren’t overly complex plants to grow, tomatoes can be prone to dozens of diseases and pests, all of which require knowledge and skill to overcome.

If you’ve grown tomatoes for a season or two, you know that occasionally, some tomato fruits will start to zipper or look like they’ve gotten stitches at some point in the growing process.

What is tomato zippering, and why does it happen? Are these Franken-tomatoes safe to eat? In this post, we’ll look at what tomato zippering is, what causes it, and how to prevent it from happening.

What is tomato zippering?

What is tomato zippering

Tomato zippering or tomato stitching happens when a long, brown scar appears on your tomato fruits, running from the stem to the blossom end of the fruit.

Sometimes, tomatoes develop more than one zippering scar, which is normal. If you see tomato zippering on your tomato crop, avoid panicking because zippering doesn’t affect the tomato’s taste – it’s only a cosmetic irregularity. The scars might criss-cross and look unsightly, but tomato zippering doesn’t affect yields or edibility.

The fact that tomato zippering is just a cosmetic issue might be one of the main reasons that zippering is a lesser-known tomato affliction. Other tomato growing problems (like blight and powdery mildew) are much more lethal and have a chance to completely decimate your crop, while tomato zippering is relatively harmless.

What causes tomato zippering?

What causes tomato zippering

According to experts, tomato zippering happens when the anther of a tomato flower sticks to the wall of the flower after pollination, as the fruit starts developing. The anther is the part of the tomato flower covered in yellow pollen when looking at a flower in full bloom.

It’s been shown that cold weather and high humidity levels contribute to the likelihood of your tomatoes developing zippering. When the air is humid, the end of the tomato flower becomes stickier. As a result, zippering becomes more probable as the anther can attach itself to new fruits with greater ease.

Cold and humidity levels aside, specific varieties of tomatoes are more susceptible to tomato zippering. Beefsteak varieties of tomatoes commonly develop zippering compared to other types of tomatoes. Generally, the larger and rounder a tomato is, the more prone it is to zippering, but if the tomato is zippering-resistant, then this rule doesn’t apply.

How to prevent tomato zippering?

How to prevent tomato zippering

There are three main topics to discuss when planning to prevent tomato zippering in your crop. One or all three may apply to your situation, so take what you feel is relevant from this list, and I hope it helps!

Buy zippering-resistant seed varieties

The best way to avoid tomato zippering is to plant tomato cultivars resistant to zippering. Look for the words “zippering resistant” in the seed description before buying any tomato seeds online if you’re interested in preventing tomato zippering or stitching.

Avoid exposing tomatoes to low temperatures

Avoid translating your tomatoes outdoors until nighttime temperatures have reached around 13 degrees Celsius or 55 degrees Fahrenheit. Fruit set on tomato plants experiencing temperatures lower than this are more likely to develop zippering.

Address humidity levels

Humidity is one of the other factors that cause tomato zippering, but this one is more difficult to address. Growers in humid climates are usually already doing as much as they can to mitigate other humidity-related tomato diseases, like powdery mildew. Growing your tomatoes in a more controlled environment, like indoors or in a greenhouse, can give you more control over the humidity levels.

Another way to reduce the negative effect of high humidity on tomato plants is to make sure your plants have adequate space between them. Check your seed packet for specific recommendations on spacing. In addition, be sure to prune your plants regularly to improve airflow, especially in humid areas.

Why prevent tomato zippering?

Why prevent tomato zippering

Home gardeners might not care about preventing tomato zippering since it doesn’t affect the flavor of your plants.

Still, tomato farmers and market growers will probably be interested in maintaining a more uniform appearance of their crops. Farmers who sell tomatoes may have difficulty moving tomatoes with blemishes and zippering because customers can be picky.

So, let’s recap: Here are the ways you can avoid tomato zippering or scarring:

  • Wait until overnight temperatures in your area have consistently reached 13 Celsius/55 Fahrenheit.
  • Plant zippering-resistant tomato varieties.
  • If your climate is humid, try growing your tomatoes in a more controlled environment where you can bring that humidity level down a bit.
  • Improve airflow between your plants by keeping them well-pruned and trimming off overlapping leaves.

What to do with tomatoes with zippering on them?

What to do with tomatoes with zippering on them

Even though tomatoes with zippering are entirely safe to eat, some people don’t like eating tomatoes that look blemished or scarred in any way. Here are some ideas for what to do with your scarred tomatoes if you’d rather not eat them whole.

  • Make tomato sauce, paste, or pizza sauce out of your scarred tomatoes. You won’t be able to see the scars on your tomatoes this way, and the sauce won’t taste any different. Tomato and pizza sauces can be frozen or canned for longer-term storage if you’re processing a large batch of scarred tomatoes.
  • Freeze the tomatoes. Sometimes during harvesting season, tomato growers are dealing with processing such a large number of tomatoes that they cannot get to every tomato before they go to waste. If this sounds familiar, throw them in a freezer-safe bag or storage container. Now you can revisit the task of processing tomatoes when you have more time on your hands, during the autumn or winter months.
  • Add them to soups. Making soup is an effective way to avoid wasting blemished and scarred produce, not just tomatoes. And soups are easy to freeze and save for later if you have adequate storage.
  • Give them away. Even if you don’t want to eat tomatoes with zippering, the fruits are still perfectly edible, and if there’s any way you can save them from being wasted, that’s ideal. See if there is a local food pantry or distribution facility near you that will take your extra tomatoes. Or, just reach out to your neighbours!
  • Sell them at a reduced price. If you sell tomatoes, know that some people will happily buy blemished or scarred tomatoes as “seconds tomatoes” or physically imperfect tomatoes. While some customers may turn up their noses at scarred tomatoes, other customers are aware that the issue doesn’t affect the taste and are happy to land a bargain.

Q&A about tomato zippering

Before we wrap up, I want to address some of the most common questions that I see being asked about tomato zippering.

Why does my tomato look like it has stitches?

Your tomato probably developed tomato zippering or stitching, a cosmetic issue. Your tomato is still safe to eat, provided the fruit has no mold.

Can you eat tomatoes with scars?

Yes! Absolutely. As long as the tomato isn’t moldy, scars and blemished don’t affect the flavour or the edibility of the tomato.

Is tomato zippering contagious?

No, not at all. Tomato zippering is not a plant disease, so it can’t be passed from one tomato plant to another. If you notice zippering on multiple neighbouring tomato plants, it’s more likely because the plants were all exposed to the same weather conditions or because they are the same tomato variety.

What tomato varieties are resistant to zippering?

Many tomato cultivars are resistant to zippering. Some examples include ‘Mountain Merit,’ ‘Better Boy, and ‘Rutgers.’ Search for “zippering-resistant” or just the word “zippering” next time you’re seed shopping to find resistant varieties.

Is tomato zippering dangerous?

No, tomato zippering is entirely safe. You can eat tomatoes with zippering as normal or elect to cut off the offending pieces of tomato if you really don’t want to eat those parts. Many tomato growers use their less-than-perfect tomatoes with zippering or cat facing to make tomato sauce, freeze, or can for long-term storage.

Are tomato cat facing and tomato zippering the same thing?

No, although the two common deformities have similarities. Cat facing happens when multiple tomato blossoms fuse to form one mega-tomato. Zippering happens when the tomato flower’s anther sticks to the side of a developing fruit during fruit set. Both issues are more likely to occur during colder temperatures.

What are some common tomato deformities?

Tomato zippering, cat facing, cracking, green shoulders, tomatoes growing “noses” or “horns,” and sun scald are all common problems that can result in misshapen or odd-looking fruits. These tomato deformities are strictly cosmetic and don’t affect the tomato’s flavour or edibility.


I hope this article has helped you learn more about tomato zippering and how to prevent it. Zippering can be unsightly, but it doesn’t have to ruin your tomato crop. With a little bit of planning, you can grow beautiful and delicious tomatoes!

Have you ever dealt with tomato zippering before? Tell me about your experience in the comments, and let’s discuss.

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