Tomato Zippering: what Causes it and how to prevent it

If you grow tomatoes, you might have seen some weird scars on your fruits that look like zippers. Don’t worry – you’re not alone! This is called tomato zippering, and it’s a common problem that many gardeners face.

In this guide, we’re going to talk all about tomato zippering. We’ll explain what causes it, how it affects your tomatoes, and most importantly, what you can do to prevent it. Whether you’re a seasoned gardener or just starting out, this information will help you grow better, healthier tomatoes.

Zippering might look strange, but it’s usually not as bad as it seems. By the end of this article, you’ll understand what’s going on with your tomatoes and how to handle it. So let’s dig in and learn all about this quirky tomato issue!

Key Takeaways:

Tomato zippering is a cosmetic issue caused by anthers sticking to developing fruits.
High humidity and cool temperatures increase the likelihood of zippering.
Some tomato varieties, like Celebrity and Roma, are more resistant to zippering.
Proper spacing, air circulation, and consistent watering help prevent zippering.
Zippered tomatoes are safe to eat and can be used in various recipes.
Pruning and managing growing conditions can significantly reduce zippering occurrence.
While zippering may affect marketability, it usually doesn’t impact overall yield for home gardeners.

What Is Tomato Zippering?

Tomato zippering is a physiological disorder that affects the appearance of tomato fruits. As the name suggests, it creates a zipper-like scar that runs from the stem end of the tomato down its side. This scar can vary in length and depth, sometimes even creating small holes in severe cases.

The distinctive feature of zippering is the thin, vertical scar on the surface of the tomato, often accompanied by short transverse scars that crisscross the vertical markings. This pattern truly resembles a zipper, hence the name. While zippering may look alarming at first glance, it’s essential to understand that it’s primarily an aesthetic issue. In other words, it doesn’t typically affect the flavor or overall quality of the tomato fruit itself.

Why Does Tomato Zippering Occur?

The root cause of tomato zippering lies in the early stages of fruit development. It occurs when the anther – the pollen-producing part of the flower – sticks to the developing fruit as it begins to grow. As the fruit expands, it pulls the anther along, creating the characteristic zipper-like scar.

Several factors can contribute to this phenomenon:

High humidity: Excessive moisture in the air can make flower parts stickier, increasing the likelihood of anthers adhering to young fruits.
Cool temperatures: Zippering tends to be more common in cooler weather, particularly during fruit set. It’s especially prevalent when temperatures drop below the optimal range for tomato fruit set (60-75°F at night and 60-90°F during the day).
Genetic predisposition: Some tomato varieties are more prone to zippering than others. For instance, Beefsteak tomatoes are known to be particularly susceptible.
Poor pollination: Incomplete pollination can sometimes lead to zippering as the flower parts don’t separate cleanly from the developing fruit.

It’s worth noting that while these factors are commonly associated with zippering, the exact mechanisms aren’t fully understood. As with many aspects of gardening, there’s still an element of mystery surrounding this phenomenon.

How Can You Identify Zippering on Tomatoes?

Identifying zippering on your tomatoes is relatively straightforward. Look for these telltale signs:

A thin, brown scar running from the stem end of the tomato down its side
The scar may be slightly raised or sunken into the fruit’s surface
Short transverse scars that crisscross the main vertical scar, enhancing the zipper-like appearance
In severe cases, small holes may be present along the scar line
The zipper-like mark is usually straight but can sometimes branch off

It’s important to distinguish zippering from other tomato fruit issues. For instance, cracking typically appears as circular patterns around the stem end, while catfacing results in more severe deformities and scarring.

Is Tomato Zippering Harmful to the Plant or Fruit?

The good news is that tomato zippering is largely a cosmetic issue. It doesn’t typically affect the plant’s overall health or the fruit’s internal quality. In fact, many gardeners find that zippered tomatoes taste just as delicious as their unblemished counterparts.

However, there are a couple of potential concerns to keep in mind:

In severe cases where zippering creates holes in the fruit, it can make the tomato more susceptible to pests and diseases.
Extensive zippering can reduce the marketability of tomatoes for commercial growers or those selling at farmers’ markets.

For the average home gardener, though, zippering is more of an annoyance than a serious problem. As the saying goes, “Beauty is only skin deep,” and this certainly applies to zippered tomatoes!

Which Tomato Varieties Are Most Susceptible to Zippering?

While any tomato variety can potentially develop zippering, some are more prone to this issue than others. Here’s a table outlining some common varieties and their susceptibility to zippering:

Tomato Varieties and Susceptibility to Zippering

Tomato Variety	Susceptibility to Zippering
Beefsteak	High
Roma	Low to Moderate
Cherry	Low
Heirloom	Varies (some high, some low)
Celebrity	Low
Early Girl	Moderate
Better Boy	Low to Moderate

It’s important to note that susceptibility can vary depending on growing conditions and individual plant genetics. If you’re particularly concerned about zippering, consider choosing varieties known for their resistance to this issue.

What Are the Best Tomato Varieties That Are Resistant to Zippering?

While no tomato variety is completely immune to zippering, some are known to be more resistant than others. If you’re looking to minimize the risk of zippering in your garden, consider planting these varieties:

Celebrity: This hybrid variety is known for its disease resistance and low susceptibility to zippering.
Roma: These oblong tomatoes are less prone to zippering and are great for sauces and canning.
Cherry tomatoes: Many cherry tomato varieties, such as Sweet 100 and Sun Gold, are less likely to develop zippering.
Better Boy: This popular hybrid variety has good overall disease resistance and is less susceptible to zippering.
Mountain Fresh: Developed for cooler climates, this variety shows good resistance to various disorders, including zippering.
Defiant PhR: Known for its disease resistance, this variety also shows good resistance to zippering.

Remember, “Variety is the spice of life.” Don’t be afraid to experiment with different tomato varieties to find those that perform best in your specific growing conditions.

How Does Weather Affect Tomato Zippering?

Weather plays a significant role in the occurrence of tomato zippering. Cool temperatures, especially during fruit set, can increase the likelihood of this issue. This is why zippering is often more common in early-season fruits or in regions with cooler climates.

To minimize weather-related zippering:

Choose planting locations wisely: Avoid areas where cold air settles, such as low spots in the garden.
Use protective measures: Consider using row covers or hoop houses to protect plants during cold spells.
Time your planting: Wait until soil temperatures have warmed sufficiently before planting your tomatoes.
Monitor nighttime temperatures: Be prepared to protect plants if temperatures drop unexpectedly during fruit set, especially if they fall below 60°F.

Remember, as the old saying goes, “Prevention is better than cure.” By taking these precautions, you can significantly reduce the risk of weather-induced zippering.

What Role Does Humidity Play in Zippering?

High humidity is another key factor in tomato zippering. When the air is very moist, the flower parts can become sticky, increasing the chances of anthers adhering to developing fruits.

To manage humidity-related zippering:

Improve air circulation: Ensure adequate spacing between plants to allow air to flow freely.
Water wisely: Water at the base of plants and avoid overhead watering, which can increase humidity around the foliage.
Consider timing: If possible, water early in the day so plants have time to dry before nightfall.
Use mulch: A layer of organic mulch can help regulate soil moisture and reduce evaporation, which contributes to air humidity.
Monitor greenhouse conditions: If growing tomatoes in a greenhouse, pay close attention to humidity levels and use ventilation or dehumidifiers if necessary.

While you can’t control the weather, these steps can help create a less favorable environment for zippering to occur.

How Does High Humidity Specifically Cause Tomato Zippering?

High humidity plays a crucial role in the development of tomato zippering. Here’s how it specifically contributes to this issue:

Increased stickiness: High humidity makes the anthers (pollen-producing parts) of the tomato flower stickier. This increased stickiness makes it more likely for the anthers to adhere to the developing fruit.
Delayed pollen release: In humid conditions, pollen may not be released as easily from the anthers. This can lead to the anthers remaining attached to the fruit for a longer period, increasing the chance of zippering.
Slower drying: High humidity slows the drying process of various flower parts after pollination. This prolonged moisture can contribute to the anther-fruit adhesion.
Fungal growth: While not directly causing zippering, high humidity can promote fungal growth, which may weaken the plant and make it more susceptible to various disorders, including zippering.

To manage humidity-related zippering:

Ensure good air circulation around plants
Water at the base of plants to avoid increasing humidity around foliage
If using a greenhouse, monitor and control humidity levels

As the saying goes, “Knowledge is power.” Understanding how humidity affects your tomatoes can help you take proactive steps to prevent zippering.

Can Proper Plant Spacing Prevent Zippering?

Proper plant spacing is indeed a crucial factor in preventing tomato zippering. When plants are too close together, it can lead to poor air circulation and increased humidity around the foliage and flowers. This creates an environment conducive to zippering.

To ensure optimal spacing:

Follow recommended spacing guidelines: Most tomato varieties should be spaced about 18-24 inches apart in rows that are 3-4 feet apart.
Consider the growth habit: Indeterminate varieties may need more space than determinate ones.
Use support structures: Trellises, cages, or stakes can help keep plants upright and improve air flow.
Avoid overcrowding: Resist the temptation to squeeze in “just one more plant” – your tomatoes will thank you for it!

Remember, “Good things come to those who wait.” While it might seem like you’re wasting space initially, proper spacing will lead to healthier plants and potentially fewer issues with zippering in the long run.

How Does Pruning Impact Tomato Zippering?

Pruning can play a significant role in managing tomato zippering. By removing excess foliage, you can improve air circulation around the plant and reduce humidity levels. However, it’s important to strike a balance – overzealous pruning can stress the plant and potentially exacerbate issues.

Here are some pruning tips to help prevent zippering:

Remove suckers: These are the small shoots that grow between the main stem and branches. Removing them can improve air flow and direct the plant’s energy towards fruit production.
Thin out dense foliage: Remove some of the interior leaves to allow better air circulation.
Prune lower leaves: As the plant grows, remove leaves near the ground to improve air flow and reduce disease risk.
Be gentle: Always use clean, sharp tools and make clean cuts to avoid damaging the plant.
Avoid excessive pruning: Over-pruning can increase the likelihood of zippering, so maintain a balanced approach.

For more detailed information on tomato pruning techniques, you can refer to this comprehensive guide from the University of Minnesota Extension.

Are There Any Specific Growing Conditions That Can Reduce the Occurrence of Zippering?

Indeed, certain growing conditions can help reduce the likelihood of tomato zippering. Here are some specific conditions to aim for:

Optimal temperature range: Maintain temperatures between 60-75°F at night and 60-90°F during the day, especially during flowering and early fruit set.
Moderate humidity: Aim for relative humidity levels between 65-75% to reduce the stickiness of flower parts without promoting fungal growth.
Good air circulation: Ensure plants are spaced properly and consider using fans in greenhouses or high tunnels to improve air movement.
Consistent soil moisture: Use mulch and regular watering to maintain even soil moisture, reducing plant stress.
Adequate sunlight: Ensure plants receive at least 6-8 hours of direct sunlight daily for optimal growth and development.
Proper soil pH: Maintain soil pH between 6.0 and 6.8, which is optimal for nutrient uptake in tomatoes.

Remember, “The devil is in the details.” Paying attention to these specific growing conditions can significantly reduce the occurrence of zippering in your tomato crop.

Are There Any Cultural Practices That Can Reduce Zippering?

Indeed, several cultural practices can help reduce the incidence of tomato zippering. These practices focus on creating an optimal growing environment for your tomatoes:

Soil management: Ensure your soil is well-draining and rich in organic matter. A soil test can help you determine if any amendments are needed.
Proper fertilization: Avoid over-fertilizing, especially with nitrogen, as this can promote excessive vegetative growth at the expense of fruit development.
Consistent watering: Maintain even soil moisture through regular watering and mulching. Fluctuations in soil moisture can stress the plant and potentially contribute to zippering.
Crop rotation: Avoid planting tomatoes in the same spot year after year to prevent soil-borne diseases and pest build-up.
Companion planting: Some gardeners swear by planting basil or marigolds near tomatoes to improve overall plant health.
Temperature management: If possible, protect your plants from cold snaps during flowering and early fruit set, as these conditions can exacerbate zippering.

Remember, “An ounce of prevention is worth a pound of cure.” Implementing these practices can help prevent zippering and contribute to healthier and more productive tomato plants.

Can Zippering Be Prevented by Using Certain Soil Types or Fertilizers?

While soil type and fertilization don’t directly prevent zippering, they can contribute to overall plant health, which may indirectly reduce the occurrence of this disorder. Here’s what you should know:

Soil type: Well-draining, loamy soil rich in organic matter is ideal for tomatoes. This type of soil helps maintain consistent moisture levels and provides good aeration, both of which contribute to plant health.
Balanced fertilization: Use a balanced fertilizer with an NPK ratio close to 5-10-5 or 5-10-10. Avoid excessive nitrogen, which can promote vegetative growth at the expense of fruit development.
Calcium supplementation: While not directly linked to zippering, adequate calcium can improve overall fruit quality. Consider adding lime or gypsum to your soil if a soil test indicates low calcium levels.
Organic matter: Incorporate compost or well-rotted manure into your soil to improve its structure and nutrient-holding capacity.
Micronutrients: Ensure your soil has adequate levels of micronutrients like boron and zinc, which play roles in flower and fruit development.

How Does Tomato Zippering Differ from Other Fruit Deformities?

While tomato zippering may seem similar to other fruit deformities at first glance, it’s important to distinguish it from other common issues. This knowledge can help you accurately diagnose problems in your tomato patch and take appropriate action.

Here’s a comparison of zippering with other common tomato fruit issues:

Fruit Issues and Descriptions

Issue	Description	Cause	Appearance
Zippering	Thin scar running down the side of the fruit	Anther sticking to developing fruit	Zipper-like line with transverse scars
Cracking	Splits in the skin of the fruit	Rapid fruit growth, often due to fluctuating water levels	Circular or radial cracks, usually near the stem end
Catfacing	Severe scarring and malformation	Cool temperatures during fruit set, excessive pruning	Large, irregular scars, often with holes or indentations
Blossom End Rot	Dark, sunken area at bottom of fruit	Calcium deficiency, often due to inconsistent watering	Large, dark patch on the bottom of the fruit

For more information on these and other tomato fruit problems, the Clemson Cooperative Extension offers a comprehensive guide.

Can You Still Eat Zippered Tomatoes?

Absolutely! The beauty of zippered tomatoes might only be skin deep, but their flavor remains unaffected. These fruits are perfectly safe to eat and often taste just as delicious as their unblemished counterparts.

Here are some key points to remember about consuming zippered tomatoes:

Safety: Zippering is a cosmetic issue and doesn’t affect the safety of the fruit.
Flavor: The taste and texture of the tomato are typically unaltered by zippering.
Nutrition: The nutritional value of zippered tomatoes remains the same as non-zippered ones.
Preparation: You may want to cut away the zippered part if it’s particularly pronounced or has created holes in the fruit.

As the saying goes, “Don’t judge a book by its cover.” The same applies to zippered tomatoes – they may not win any beauty contests, but they can still be the star of your salad or sauce!

What Are the Best Ways to Use Zippered Tomatoes?

While zippered tomatoes are perfectly fine to eat fresh, their appearance might make them less appealing for certain uses. Here are some great ways to make the most of your zippered tomatoes:

Sauces and soups: Cooked and pureed tomatoes are perfect for hiding any skin imperfections. Try making a classic marinara sauce or a comforting tomato soup.
Salsa: Diced tomatoes in salsa won’t show any signs of zippering. Whip up a batch of fresh salsa for your next gathering.
Canning: If you have a lot of zippered tomatoes, consider canning them for future use. The National Center for Home Food Preservation offers safe canning guidelines.
Roasting: Roasted tomatoes are delicious and any zippering will be hardly noticeable. Try this simple roasted tomato recipe.
Tomato jam: Turn your zippered tomatoes into a unique and tasty tomato jam.

Remember, “Waste not, want not.” With a little creativity, your zippered tomatoes can be transformed into delicious dishes that everyone will enjoy.

How Does Zippering Affect the Overall Yield of a Tomato Plant?

Tomato zippering, while primarily a cosmetic issue, can have some impact on the overall yield of a tomato plant. Here’s how:

Marketability: For commercial growers, zippered tomatoes may be less marketable, effectively reducing the sellable yield.
Fruit size: In severe cases where zippering creates deep scars or holes, the affected fruits may be smaller than unaffected ones.
Susceptibility to secondary issues: Tomatoes with severe zippering may be more prone to cracking or pest invasion, potentially reducing the usable yield.
Plant stress: While zippering itself doesn’t stress the plant, the conditions that cause it (like temperature fluctuations) might affect overall plant health and productivity.
Minimal impact on home gardens: For home gardeners, the impact on yield is often negligible, as zippered tomatoes are still perfectly edible.

It’s important to note that in most cases, especially for home gardeners, the impact of zippering on overall yield is minimal. As the adage goes, “Don’t count your chickens before they hatch.” While zippering may affect some fruits, a healthy tomato plant will still produce plenty of delicious tomatoes for your table.

How Can You Prevent Tomato Zippering in Future Seasons?

While it’s not always possible to completely eliminate zippering, there are several steps you can take to minimize its occurrence in future growing seasons:

Choose resistant varieties: Some tomato varieties are less prone to zippering. Research and select varieties known for their resistance.
Optimize growing conditions: Ensure your tomatoes have proper spacing, good air circulation, and consistent watering.
Monitor temperature: Protect your plants during cold spells, especially during flowering and early fruit set. Maintain temperatures within the optimal range of 60-75°F at night and 60-90°F during the day.
Manage humidity: Improve air circulation and avoid overhead watering to reduce humidity around plants. In greenhouses, use ventilation or dehumidifiers if necessary.
Practice proper pruning: Remove suckers and thin out dense foliage to improve air flow, but avoid over-pruning.
Rotate crops: Avoid planting tomatoes in the same spot year after year to prevent soil-borne issues.
Maintain soil health: Ensure your soil is well-draining and rich in organic matter. Consider getting a soil test to identify any nutrient deficiencies.
Time your planting: Wait until soil temperatures have warmed sufficiently before planting your tomatoes.

As the old gardening adage goes, “The best fertilizer is the gardener’s shadow.” Regular observation and care of your tomato plants can go a long way in preventing issues like zippering.

Conclusion

Tomato zippering, while unsightly, is a manageable issue that shouldn’t deter you from enjoying homegrown tomatoes. By understanding its causes and implementing preventive measures, you can significantly reduce its occurrence in your garden. Remember, even if you do end up with some zippered tomatoes, they’re still perfectly edible and can be used in a variety of delicious ways.

Happy gardening, and may your tomato harvest be bountiful and (mostly) zipper-free!