7 Reasons Why Your Squash Grows Bitter (Easy Solutions)

Squash is not only delicious but also a highly nutritious veggie that can spruce up any dish, from a colorful summer salad to a hearty winter soup. By growing the plant yourself, you’ll be able to achieve a much better taste and micronutrient content for a fraction of the price. However, it can be disheartening to harvest the product of your hard work, only to find that your squash is bitter.

Here are seven reasons why your squash grows bitter:

  1. The plant has produced cucurbitacin compounds.
  2. There have been unexpected temperature swings.
  3. You haven’t picked it at the right time.
  4. The plant isn’t grown in ideal conditions.
  5. The seeds have been cross-pollinated.
  6. The plant is suffering from a disease.
  7. The bitter taste is genetic.

In this article, you’ll learn more about each of the causes that might be making your squash taste bitter, including why they occur, how you can fix them (when possible), and how to prevent them from happening next season.

1. The Plant Has Produced Cucurbitacin Compounds

All squash grown without any additives are prone to a slightly bitter taste, which occurs due to the plant’s genetic composition. 

As you’ll see in one of the following sections, some varieties are more susceptible to a bitter taste than others. However, all of them produce a class of chemical compounds called cucurbitacin, which is responsible for the unpleasant flavor you might be experiencing.

Cucurbitacin chemicals are often produced as a defense against herbivores. When plants belonging to the Cucurbitaceae family (squash included) feel they’re threatened, they release cucurbitacin as a taste deterrent to protect them from any possible attacks. 

When your plant experiences excessive amounts of stress, it releases a higher level of cucurbitacin chemicals, which, in turn, will make the squash taste much more bitter.

For example, wild cucurbits produce excessive levels of these chemical compounds due to the unsafe environment they grow in. For this reason, most wild varieties are completely inedible, both due to taste and safety concerns. 

On the other hand, commercially-grown varieties are not only genetically predisposed to release fewer cucurbitacin compounds, but they also develop in much more suitable environments that allow them to optimize their taste.

However, even if you’re growing the plant yourself, if the phenomenon has made it bitter enough, there’s no way to fix it apart from incorporating it intentionally in a dish that requires its flavor profile. For this reason, it’s important to prevent excessive levels of cucurbitacin from being produced altogether.

You can do so by keeping an eye on your produce while it grows to identify any possible stress sources and eliminate them before they can affect your vegetable’s taste too much.

Can You Eat Bitter Squash?

You can eat bitter squash, but only in small quantities. Cucurbitacin compounds (which cause the bitter taste in squash) aren’t usually toxic or poisonous. However, they can cause digestive discomfort and other severe health problems when consumed in excess.

In short, although consuming bitter squash likely won’t kill you, in some cases, it can cause severe health implications. These implications can include diarrhea, vomiting, stomach cramps, and overall digestive discomfort. 

In severe cases, some complications can even lead to death. Not to mention the taste itself will be unpleasant, making the overall experience not worth the risk. 

Therefore, although you may not want to discard the product of your hard work, it might be best to do so and consider the process a learning experience to take with you through the next squash season. 

If there’s a particular dish that requires the addition of a bitter taste profile, you can go ahead and make use of your produce. However, as mentioned, be careful not to consume in excess to avoid the previously mentioned risks.

All naturally grown squash is susceptible to a slightly bitter taste. For this reason, it might feel challenging and confusing to pick out the vegetables that are safe to consume and those that aren’t. In this scenario, it’s always best to follow your tastebuds.

If the bitter flavor is mild and doesn’t take from the plant’s pleasant taste and aroma, then it’s probably safe to eat. However, if the bitterness is overwhelming enough to make the eating experience unenjoyable, it’s best to avoid consuming your harvest.

Never consume wild squash varieties, as it could be more dangerous than you’d think.

Lastly, to prevent the phenomenon from happening again, ensure to throw out any seeds you might’ve saved from the affected plant. The compounds don’t only influence the vegetable itself, but its seeds as well, which means that using them for the following season would set you up for failure.

2. There Have Been Unexpected Temperature Swings

The stress receptor responsible for producing cucurbitacin compounds in squash isn’t only triggered by physical stress but by environmental stress as well. Unstable weather conditions accompanied by sudden temperature swings could significantly impact the taste of your produce.

This phenomenon is especially common if you’ve managed to plant your squash during the end of their season when temperatures start to change drastically. As long as these changes aren’t too sudden or extreme (e.g., hot sunny weather one day and heavy rain or snowfall the other), the taste shouldn’t be impacted too much, and the bitter flavor should be mild and tolerable.

Not all produce is affected equally by sudden temperature swings. Some veggies might suffer more than others under environmental stress depending on their positioning, nutrient retention, and age.

Also, if the said environmental stress is temporary, chances are the bitter flavor hasn’t had enough time to penetrate deeper than the skin. For this reason, a simple peel would usually suffice to make the squash safer (and tastier) to consume.

Squash plant after the first frost

The best thing you can do to prevent your squash from getting bitter is to grow them during the season when soil temperatures remain well between 60 and 85 °F (15.6 and 29 °C).

3. You Haven’t Picked It at the Right Time

Finding the right time to pick your squash can significantly affect its taste and texture. No matter whether you’re growing your produce during the summer or winter season, it’s always crucial to pay attention to the timing of your harvest.

Winter squash might require additional care and attention to ensure you’re picking it when it’s fully ready. 

You’ll want to harvest winter squash as soon as its rind gets dark and thick enough. Its exterior should have turned a deeper color that can range from golden yellow to orange, while its skin should have become strong enough for you not to be able to easily penetrate it with a fingernail.

If you’re not confident in your observational skills, you can schedule your harvest around frost times. 

Generally speaking, you’ll want to pick your winter squash before the first frost. However, this is more of a guideline than a hard-set rule, and depending on the specific temperatures and conditions in your area, you might want to customize your schedule to tailor it to your plant’s growth rate.

Picking your squash while it isn’t done developing yet might lead to a bitter, unpleasant flavor that would render the vegetable inedible. On the other hand, leaving your plant out in freezing temperatures longer than what it can handle could lead to a similar result, not to mention doing so would significantly decrease its lifespan.

Luckily, summer squash is more forgiving when it comes to harvest times. The vegetable retains its flavor much better throughout its growth period, which means you can safely harvest and consume it at almost any size.

Yet, timing isn’t the only factor you’ll want to consider when it comes to picking your squash. The way you go about it also matters. As I previously mentioned, external stress could make the plant produce extensive amounts of cucurbitacin compounds, which you know by now is the main cause of squash’s bitter taste.

For this reason, you’ll want the harvesting process to be as quick and efficient as possible. To achieve this, you’ll want to use sharp, clean pruners that can detach the plant with one single move.

Just be careful not to cut off the entire stem, as leaving about 2 inches (5 cm) still attached could do wonders for your vegetable’s longevity.

4. The Plant Isn’t Grown in Ideal Conditions

Temperature isn’t the only environmental factor that could put external pressure on your plants. Squash requires specific conditions for it to develop its ideal taste and texture. Otherwise, both will suffer.

Humidity

For example, depending on the type of squash you’re growing, humidity levels will need to be balanced and constant for the plant not to feel the effect of an external stressor. Low outdoor humidity (around 30%) is crucial to avoid moisture-related problems, such as pests and diseases.

Nutrients

You’ll also want to provide your squash with the necessary nutrients and minerals to ensure optimal growth. They need a balanced fertilizer with an NPK ratio of 10-10-10 in the soil as the seedlings sprout to get them to a good start. They also need another boost right before they bear fruits.

When the vegetable doesn’t receive the nutritional value it requires, this will be interpreted as an immediate threat, resulting in a bitter taste.

Sunlight 

Another environmental factor you’ll want to keep an eye on is sun exposure. Squash doesn’t grow well in shadows and will be less likely to produce good-quality fruits. The plant requires at least six hours of sunlight a day to develop normally. 

Water

You should apply care and consistency when it comes to your watering practices. Soil that’s too wet or dry could severely hamper your plant’s development. However, the consistency of your watering practices can sometimes be just as detrimental, even when the overall moisture levels are balanced.

For example, if you overwater your squash one day and forget to water it altogether the other, this will create a less-than-ideal environment for the plant to thrive in.

In general, squash needs about an inch of water per week or about six gallons per square yard (22.7 liters per 0.8 square meter).

Squash has deep and shallow roots, so it’s essential to add enough water to hydrate the top 8 inches (20 cm) of the soil every time you water your plant. This ensures that the root zone has access to enough water before it’s lost through soil seepage or evaporation.

It’s also crucial to keep the vegetable’s leaves from getting wet, as doing so can invite pests and pathogens that can stress the plant.

Soil pH

Nutritional value and moisture levels aren’t the only factors you should be worrying about. Unideal pH levels could also cause pressure on your plant, which is why you’ll always want to keep an eye on (and regulate if necessary) the soil’s acidity. 

Generally, it’s best to keep the ground’s pH level in a range between 6 and 6.5. Squash thrives in a slightly acidic environment. Soil nutrients are readily accessible to your squash plant’s roots if the soil pH stays within this range.

5. The Seeds Have Been Cross-Pollinated

Cucurbitacin compounds are stronger than you’d think. They don’t only affect the taste and chemical composition of the plant producing them, but its seeds as well. And as you’ll see in this section, neighboring plants could also be affected due to cross-pollination carried out by bees and other similar insects.

This is just one of the many reasons why prevention is always better (and more achievable) than cure when it comes to combating cucurbitacin. If the phenomenon has already occurred, there are a few factors you’ll want to remember in order to keep it as contained as possible.

It doesn’t help that it’s often very challenging to save the seeds of a member of the Cucurbitaceae family. The reason for this is that the species have a significant number of inedible relatives, with which they’re predisposed to cross-pollinate. 

As long as bees and other similar insects hover around your plants, there’s always a possibility you’ll end up with a new, inedible breed in your garden sooner than later.

However, this isn’t something that can only happen to casual gardeners or the inexperienced. Even commercially sold squash seeds can often turn out to be a cross-bred variety, resulting in a bitter and texturally strange harvest.

Therefore, if you’ve provided your plant with its ideal environmental conditions and you still end up with a bitter-tasting squash, chances are the seeds you used weren’t setting you up for success.

Usually, you’ll be able to spot a cross-pollinated squash simply by looking at it. So if you feel like your product is looking disproportionate—bigger than normal or strange overall—it might be a good idea to put off its consumption until you can get a better understanding of the situation.

It’s important not to rush into tasting these strange-looking vegetables, as cross-pollinated varieties are not only unpleasant-tasting but can sometimes be harmful to your health as well.

Choosing the right seeds to save and use can get even more challenging given that sometimes a plant affected by cucurbitacin compounds doesn’t exhibit bitterness itself, but rather it transmits the chemical’s genetic code to its offspring.

Ideally, you’d always want to save the seed coming from squash that’s been isolated and pollinated with pollen that comes from domesticated varieties. Keeping your plants from cross-pollinating with bitter variants is a skill that requires time and practice to perfect, so don’t get discouraged if you get it wrong the first few times.

Those wanting to perfect their seed-saving skills are in luck. In the following section, I’ll take you through a few steps you can follow to ensure your plants won’t be pollinated by undesirable squash varieties.

How to Save Squash Seeds

Differentiate Between Male and Female Flowers

First, learn to tell male and female squash flowers apart. Usually, there are plenty of visual differences that help you distinguish the two. For example, female flowers have miniature fruits at their base, which their male counterparts don’t. Male species are generally attached to longer, stronger stalks.

Monitor Soon-to-Open Flowers

Keep an eye on the flowers that are about to open. Every evening, inspect your plants closely to spot any flowers that are likely to open the following day. Prevent them from spreading independently. Usually, the day before they bloom, squash flowers have a fairly pointed tip, which you’ll want to be looking out for.

Close the Flowers During the Night

Using any type of (gentle) tying technique, you’ll want to close all about-to-open flowers throughout the night. 

Carry on the Pollination Process

Open up the flowers, take some pollen from the male flower, and add it to the center of the female flower. Afterward, you’ll want to close the female flower again to avoid any possible cross-pollination from insects or bees. You’ll want to make note of the plants you’ve done this to.

By following these steps, you’ll be able to save and reuse the seeds with absolute peace of mind. 

Although going through this process might seem tedious, it’s the only way that can keep you from entering a vicious cycle that always ends with the harvest of bitter, cross-pollinated crops. This guide will help you grow healthy, delicious squash one season after the other, which makes the process a worthy investment in terms of both money and time.

6. The Plant Is Suffering From a Disease

Although it can be easy to put the blame on cucurbitacin production when it comes to bitter squash, sometimes the cause can be much simpler.

As with any other type of plant, squash is also susceptible to a wide range of diseases and infections. Their effect can be multi-fold, with a bitter, unpleasant flavor being one of the most common complications.

There’s a wide range of pests and diseases that can affect squash. However, you’ll especially want to look out for the following:

Powdery Mildew

Powdery mildew is one common fungus variety that affects cucurbits. Luckily, its appearance makes it easily identifiable, as you’ll quickly notice the white, powdery marks that they leave on top of the infected areas.

Squash is exceptionally susceptible to this condition during warm months, so if you’re growing a summer variety, this is something you’ll want to look out for. 

There are some ways for you to treat powdery mildew when it comes to your particular Cucurbitaceae variety, but preventing the phenomenon from happening altogether will give you a much better chance of harvesting healthy, delicious veggies.

Powdery mildew thrives even in dry conditions, making them unique from other fungal diseases. However, the spores spread when there’s high humidity so it’s crucial to maintain low humidity around your plant. It’s also important to maintain good spacing and airflow among your plants.

Other Fungal Infections

When it comes to fungal infections, powdery mildew is usually the least of your problems. Other similar conditions can lead to your plant’s rotting much quicker, and there’s generally very little you can do about it.

If the infection goes unnoticed for too long, it can affect the entire root system, spoiling much more than just a single plant. Upon noticing an infected squash, the only thing you can do is pluck it from the roots as soon as possible and dispose of it. By doing so, you’ll ensure the disease doesn’t spread to neighboring roots.

This is also something you’ll want to consider during the planting process as well. Opting for a sterilized variety of soil could help significantly reduce the possibility of a fungal infection. 

Pests

The organisms damaging your plant aren’t always on the micro level. When looking for pests that attack the Cucurbitaceae variety, you’ll generally want to look for the usual offenders: aphids and snails. Both can severely damage your produce in different ways.

While the damage caused by snails or slugs is usually much more extensive, it’s also easier to spot and troubleshoot.

Slugs and snails come out at night and search for moist soil. Therefore, to keep them from attacking your squash, avoid watering in the evening. Water your plant in the morning to give the soil surface ample time to dry during the day.

On the other hand, aphids are less likely to damage your plant within a limited amount of time, but they can often go unnoticed. 

As discussed, it’s best to avoid wetting the foliage as much as possible. But when treating an aphid infestation, you can remove them by spraying them with water from your garden hose. Just ensure adequate air circulation to prevent the leaves from staying wet for too long.

You may also consider thinning the foliage if the plants are becoming too crowded.

7. The Bitter Taste Is Genetic

You can save the purest seed, grow your squash in the best conditions, prevent pests and infections as much as you can, and your end product might still come out tasting bitter. It can be frustrating to no end, but that’s just a risk you take when choosing to grow a member of the Cucurbitaceae family.

These species are genetically predisposed to a level of bitterness, with some more than others. Additionally, given that cucurbitacin production is one of their main defense mechanisms, there are bound to be some chemical compounds present in the vegetable you eat.

Remember that mild bitterness can sometimes add to the enjoyment of eating squash. However, stay away from overly unpleasant varieties and use their growth process as a learning curve to do better next season.

Dr. Moritz Picot

Dr. Moritz Picot is a horticulture enthusiast and the founder of TheGrowingLeaf.com, where he serves as the lead content writer. He established the website in 2022 as a valuable resource for both gardening aficionados and beginners, compiling all the gardening tips he has accumulated over the past 25 years. Alex has a passion for nurturing plants, transforming backyards into inviting spaces, and sharing his knowledge with the world.

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