Why Is Your Spinach Growing Bitter? 5 Causes

Spinach can be tricky to grow. If harvested under certain conditions, it can become bitter. So why does spinach become unpalatable on occasion? 

Spinach may grow bitter because:

  1. The soil quality doesn’t meet spinach’s growing requirements.
  2. Your spinach was planted late in the growing season.
  3. The soil is too dry for growing spinach.
  4. The spinach was harvested too late.
  5. Spinach has a natural bitter taste.

This article explains the conditions that cause spinach to taste bitter. It also has handy tips to avoid this problem so you can continue to enjoy eating these leafy greens.

1. The Soil Quality Doesn’t Meet Spinach’s Growing Requirements

Soil quality is one of the main factors influencing spinach’s taste after harvest. It’s a short plant that requires a moderate amount of nutrients. However, a lack of organic matter can cause significant problems. 

If the soil you’re growing spinach in doesn’t have enough organic matter, it will stress the plant out and cause premature bolting. This means that the plant shifts its focus and starts producing flowers, which turn into seeds. As a result, the leaves start to get a bitter aftertaste. 

The longer you allow that unwanted foliage to remain on the spinach, the stronger the unpalatable taste becomes. 

Benefits of Organic Matter

Other benefits of sufficient organic matter in the soil for spinach include the following:

Improves Soil Characteristics

Improving the soil’s characteristics make it viable for different flora. For example, when the soil has a high amount of clay, it doesn’t drain water quickly.

Further, the consistency of clay prevents it from retaining oxygen. Sandy soil also doesn’t hold water as well as clay does. Adding organic matter makes up for any shortcomings these soils may have. 

Provides a Steady Flow of Nutrients

The microbes in the soil decompose the organic matter and convert it into nutrients for spinach, promoting the growth of foliage.

Prevents Dense Soil

Organic matter prevents the soil from becoming dense and ensures that the roots penetrate the land efficiently. This is important because spinach plants have shallow roots. The roots have to anchor the plant well despite their shallow reach.

Better Aeration

Organic matter improves soil aeration as well. By adequately aerating the soil, you ensure a healthy balance of life in it. 

Improved Moisture Retention

Adding this matter also improves the soil’s ability to retain moisture and reduces the risk of water stress. Spinach is sensitive to the water level in the ground and can prematurely bolt if the soil moisture is below its requirements. 

How to Fix

The general rule is that your soil should contain at least 2% organic matter by weight. Luckily, organic matter isn’t hard to come by, as it’s essentially any living or dead material. 

Before adding organic matter to the soil for your spinach, here are a few things to keep in mind:

Only Use Just Enough Organic Matter

Ensure you only use enough organic matter to satisfy your spinach plant’s needs.

As highlighted earlier, organic matter releases nutrients slowly into the soil. This is fine during the initial growth phase as there isn’t an abundance of nutrients. Over time, however, these nutrients can accumulate and become too much for your plant.  

Do a Soil Test

A soil test will tell you what nutrients your soil has and what it lacks. You can get a soil test kit from any garden center or online.

Consider Compost or Plant Debris

You don’t need to break the bank to add more organic matter to your soil. Most of what you need can be found around the house. 

For example, instead of throwing away kitchen scraps, you can reuse them as compost. You can also collect clippings from mowed grass and use them to enrich your soil. Basically, plant debris, as long as it isn’t infected with diseases or pests, can work as organic matter. 

2. Your Spinach Was Planted Late in the Growing Season

Aside from the soil quality, the weather significantly affects the taste of your spinach. Spinach plants cannot tolerate high temperatures or increasing daylight. Both can force the plant to bolt, even if you’re growing slow-bolting varieties. 

For example, if you plant spinach late into spring because you don’t have much time to tend to the garden, the temperature will increase and go beyond 85 °F (29 °C) once it hits summer in your region. 

Conversely, if you wait too long during the fall season to plant, the lower temperatures can cause vernalization, which in turn leads to premature bolting. 

Either way, you won’t be able to harvest the spinach leaves because they’ll already have a strong bitter taste. 

How to Fix

Plant During the Right Time or Temperature

Figuring out the best time to plant spinach can be more difficult than it sounds. After all, if you have a certain temperature range today, there’s no guarantee that it’ll be the same temperature 365 days from now. 

When planting your spinach, the temperature should be in the 60 °F (15.5 °C) range. This is the range where your spinach is least likely to grow bitter.

If you’re aiming for a summer harvest, plant in early spring. Do it 4 weeks before the last average frost to avoid vernalization. 

You could also plant your spinach in early fall. This is the only other season you can grow spinach, as the chances of the plant bolting are relatively low. 

Harvest the spinach when the temperature in your area goes beyond 85 °F (29 °C). Also, as soon as you notice it producing seed stalks, harvest it immediately.

Use Floating Row Covers

Floating row covers can likewise protect your spinach from high temperatures by providing shade. For the leaves not to taste bitter, daylight shouldn’t be more than 10 hours daily. 

However, remember that floating covers won’t help if you plant too late into the season. During peak summer, the higher temperatures and extended daylight hours will force the plant to bolt and change the taste of its leaves. 

Plant the Right Variety in the Right Season

You should go for slow-bolting varieties when planting spinach in early spring, so there’s enough time for them to grow. According to the University of Wisconsin-Madison, slow bolting varieties include Olympia, Indian Summer, and Bloomsdale. 

On the other hand, quick-bolting types work best when you’re planting in the fall since you’ll be able to harvest before winter hits your region. 

Plant Your Spinach With Other Crops

If you have no choice but to plant spinach during the summer, you can also grow summer crops that can provide shade. You shouldn’t just grow any crop, however.

The ideal companion plant for your spinach shouldn’t take up too much space in your garden or take away vital nutrients from it. You can grow some good plants with spinach, including peppers and tomatoes.

3. The Soil Is Too Dry for Growing Spinach

If there isn’t enough water in the soil, your spinach will experience water stress. Like people, spinach plants adversely react to extreme stress. Their leaves start to bolt, resulting in a bitter taste. 

In particular, moisture plays a crucial role when growing Malabar spinach. The ideal annual rainfall for these plants is 80-100 inches (2-2.5 m). They can even tolerate up to 160 inches (4 m) of water annually. 

An easy way to identify whether there’s sufficient water in the soil is to look at the spinach plant. If you notice the drooping leaves, the moisture level is low in the ground. In extreme cases, the plant’s foliage will wilt and fall off the plant. 

You can also remove some soil from your garden and make it into a ball. If it cannot hold this shape or breaks apart, it’s an indicator of dry soil.

How to Fix

Irrigate Your Spinach Well

Regular irrigation helps to ensure that your spinach tastes good. When you irrigate deep into the soil, you encourage your spinach plant’s roots to grow. Deeper root growth allows the plant to withstand drought-like conditions and avoid the bolting that causes the bitter taste. 

You can either water your spinach manually or with sprinklers. If using a sprinkler system, make sure you do so early in the morning. Otherwise, the higher temperatures throughout the day will cause the water to evaporate before your spinach can make use of it.  

One downside of a sprinkler system is that water droplets can land in the surrounding area and cause weeds to grow around your spinach. To avoid that, you can use drip irrigation instead. 

Drip irrigation benefits spinach plants by allowing water to go deep into the soil, reducing loss due to evaporation and the likelihood of weeds growing.

Alternatively, you can have both a sprinkler and drip irrigation system. After you sow the seeds into the soil, sprinklers are effective because of the plant’s short roots.

The roots can take water from the ground as long as it is within 6 inches (15 cm) from the surface. Once it becomes a seedling (i.e., it emerges from the ground), you can use drip irrigation.  

Before you set up an irrigation schedule, you should know how much water spinach plants require. Most types of spinach require at least an inch (2.5 cm) of water every week.

While keeping the soil moist is crucial, overwatering can also be an issue, as it can lead to root rot fatal to plants. If you’d like to avoid this, you can grow them in raised beds.

Also, remember to keep the moisture levels in the soil consistent. Large or frequent fluctuations stress the plant, giving the leaves a bitter taste.  

Cover the Soil With Mulch

You can use materials like grass clippings, sawdust, and plant debris as mulch. If you use sawdust, you may have to supplement the soil with nitrogen, as the former disrupts the nitrifying process. Again, avoid using infected plant debris, as any harmful microorganisms from it can harm your spinach.

Also, mulch should be free of weed seeds, as you don’t want unwanted flora growing along with the spinach plants. The plants will be stressed as they compete with weeds, increasing the likelihood of them bolting prematurely and making the leaves taste bitter. 

Mulches help reduce water loss in the soil due to evaporation and keep the moisture level consistent, preventing fluctuations. 

4. The Spinach Was Harvested Too Late

Just as harvesting spinach too early is a problem, harvesting it too late is also a problem. Ideally, you want to cut off spinach leaves when they reach a specific size and age. If you leave them on the plant for too long and it starts flowering, the foliage will be bitter. 

How to Fix

If you planted a little late into the fall season, don’t worry, as you can still harvest the plant. All you have to do is cut and leave only an inch or two (2.5-5 cm) of the plant above the soil.

This makes it easier for the plant to survive winter. Come spring, the plant will be ready for harvesting as usual. 

Of course, the best fix for this issue is to keep it from happening in the first place. You need to keep tabs on when you planted your spinach. Within 37-45 days, you can start removing the leaves, though the best time to do this varies depending on the type of spinach you grow.

Also, you can remove the edible foliage when you see at least 6 leaves or enough foliage to use in a meal. This is especially important for spinach grown in the fall, as you’ll give the plant sufficient time to produce more leaves. Ensure you only harvest the outer leaves initially so the inner foliage will grow and increase the size of your produce. 

Although there’s no definite size the leaves should reach before you harvest them, 3 to 6 inches (7.6 to 15 cm) is a good rule of thumb. It’s also okay if you remove the foliage when they’re tender. 

Before you thin the foliage, you should wait for the spinach to reach at least 2 inches (5 cm) in height. After this, apply a side-dressing of fertilizers to promote vegetation.

For fertilizing spinach, I recommend vegetable & herb organic fertilizers or organic fertilizers for leafy greens like spinach. By using organic fertilizers, you can feed your spinach without harming the surrounding ecosystem in any way. 

5. Spinach Has a Natural Bitter Taste

Although you don’t want your spinach to become too bitter, you should keep in mind that spinach should be somewhat bitter. 

Spinach produces phytonutrient compounds to protect itself against predators, pests, and diseases. Think of it as a natural pesticide. 

These phytonutrients also contribute to the touted health benefits of spinach, like lowering the risk of cardiovascular disease and cancer.

To date, it’s impossible to breed spinach without these vital phytonutrient compounds. Even if it is possible, there’s a risk that the spinach will lose its ability to protect itself against everything that wants to eat it.

How to Fix

You can’t completely eliminate spinach’s bitter taste, but you can make it a little more palatable. For example, you can cook it and season it with your favorite spices. If you’re using it in a salad, add olive oil dressing and salt to mitigate the unpleasant flavor. 

Final Thoughts

Spinach is naturally bitter due to the presence of phytonutrient compounds. Luckily, there are ways to ensure the plant doesn’t have a strong and unpleasant aftertaste. 

Ensure that your soil has a sufficient weight of organic matter (i.e., 2% of the total soil weight). You can also prevent the plant from bolting prematurely by following proper irrigation practices. 

The time you sow the seeds or transplant them into the soil makes a huge difference. This is because of the plant’s sensitivity to daylight and temperature.

Alexander Picot

Alexander Picot is the founder of TheGrowingLeaf.com and its lead content writer. He created the website in 2022 as a resource for horticulture lovers and beginners alike, compiling all the gardening tips he discovered over the years. Alex has a passion for caring for plants, turning backyards into feel-good places, and sharing his knowledge with the rest of the world.

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