The 6 Reasons Why Hydroponic Lettuce Taste Bitter


After weeks of growing hydroponic lettuce, you ended up with a bunch of bitter leaves. Why does hydroponic lettuce get bitter? It is probably your fault but the good news is that you can avoid such mistakes!

Hydroponic lettuce may taste bitter due to: 1) too much nutrients, 2) high calcium content, 3) growing in the summer heat, 4) the lettuce cultivar, 5) improper storage, 6) and supertasters. These reasons can be addressed by flushing excess mineral salts, growing during the colder season, choosing the proper cultivar, and proper storage, respectively.

The taste of bitterness in hydroponic lettuce and soil-cultivated lettuce have common reasons which can be addressed quickly! Any grower shouldn’t have to suffer unwanted bitterness either for profit or for pleasure.

Is It Normal For Hydroponic Lettuce To Be Bitter?

Hydroponic lettuce should taste no different from soil-cultivated lettuce. A study by the Department of Nutrition in the University of Nevada showed that there was no noticeable visual or sensory difference between lettuce grown traditionally or hydroponically – be it taste, appearance, or odor, among others.

Hence, the taste of bitterness in hydroponic or soil-cultivated lettuce has common reasons and solutions. The only two major differences between hydroponics and soil-cultivated plants are that hydroponic plants: 1) should grow faster and larger, and 2) should have greater nutritional content.

Hydroponic lettuce taste bitter – Infographic

6 Reasons Why Hydroponic Lettuce Tastes Bitter

The 6 reasons why hydroponic lettuce may taste bitter are 1) too much nutrients, 2) high calcium content, 3) growing in the summer heat, 4) the lettuce cultivar, 5) improper storage, 6) and supertasters.

One by one, let’s discuss all the reasons and the solutions to address them.

1 – Too Much Nutrients

An overabundance of nutrients is not good for plants. It will cause nutrition stress which leads to degradation in plant health, alteration in the plant’s appearance and taste, and even plant death.

Excess of mineral salts, most notably nitrogen (N), contributes to the bitter taste of lettuce. Even though nitrogen is an essential macronutrient in the nitrogen-phosphorus-potassium (NPK) triangle, overabundance is as damaging as nutrient deficiency. Any nutrient imbalance should be properly adjusted.

Furthermore, there is a potential health risk with too much nitrogen in the form of nitrates in lettuce leaves which is why there is EU legislation regulating a threshold of nitrate content. The nitrate content in leafy green vegetables in the diets of people can have adverse effects.

Solution

As with any case of nutrient imbalance in a medium (i.e. applicable to soil or nutrient solution in hydroponics), the simplest solution is flushing. Flushing means removing unwanted mineral salts from a growing medium.

Flushing in hydroponics involves draining the water from the reservoir and refilling it with fresh water. The reservoir without any nutrients will be allowed to circulate in the system which would also flush the roots of any unwanted mineral salts. After the negative effects of too much nutrients have subsided (i.e. nutrient burn), little by little, nutrients can be reintroduced into the nutrient reservoir.

The College of Agricultural Sciences by the Pennsylvania State University has a formula guide on how to calculate nutrients in a system. This is especially useful for a grower who wants to preemptively micromanage the nutrient content in their system.

2 – High Calcium Content

Bitterness in hydroponic lettuce can be linked to high calcium content. It is possible the nutrient reservoir contains too much calcium which will be absorbed by the lettuce thereby permanently affecting its taste.

A study shows that there is a high correlation between calcium content and the taste of bitterness. Twenty-four (24) vegetables were tasted by a sample size of 35 people and vegetables which contained greater calcium content tasted more bitter than those with less calcium content.

Even though the study itself does not list lettuce among the vegetables sampled, the presence of cruciferous vegetables such as bok choy, cabbage, spinach, and kale, among others, would suggest that the correlation would apply to other leafy vegetables. Lettuce and cruciferous vegetables are similar insofar that the edible portions are the leafy parts. Greater calcium content in these edible portions would significantly contribute to the taste of bitterness.

Solution

Similar to plant stress due to too much nutrients, the practice of flushing applies to too much calcium.

The nutrient reservoir should be flushed and replaced with fresh water. The newly refilled reservoir water should be allowed to recirculate to allow the plant to recover from the unwanted excess calcium intake.

Prevention is always preferred over a cure. Growers should be wary of how much calcium they incorporate into their nutrient reservoir by calculating the estimated nutritional content as shown in the above Pennsylvania State University link. Calcium, though an essential macronutrient in plants that strengthen cell structures and act as intracellular messengers, can be detrimental to plant health when in excess.

3 – Growing in the Summer Heat

Lettuce is a cool-season crop that grows and tastes best when temperatures are low. When lettuce is grown during the summer season, it will mature quickly, producing flowers and seeds instead of leaves way ahead of usual. Hence, it is a common mistake to harvest lettuce too late if grown in summer making it taste bitter.

In this case, the lettuce is said to“bolt”. In this stage, it undergoes chemical processes as a defense mechanism against insects. This process is irreversible. As such, it is better to harvest lettuce when they are young since they have not matured yet.

Solution

There are two solutions to prevent lettuce from becoming bitter due to seasonal temperatures: 1) grow during the colder seasons, and 2) grow indoors.

Obviously, it’s better to grow lettuce during the colder seasons since low temperatures (60-70°F or 15.56-21.1°C) would not induce rapid maturation that would create seeds and flowers. Planting in the spring or fall would provide the lettuce the desirable growing temperatures that will prevent it from developing a bitter taste.

Growing indoors presents an all-season solution to the problem. Growing indoors can allow the grower to manually adjust the temperature to be suitably cold. Additionally, the shade provided indoors allows for passive cooling, preventing direct sunlight from increasing the ambient temperature.

4 – Lettuce Cultivar

Different lettuce cultivars (plant varieties created through selective breeding) contribute to taste profiles. Genetic variations in and between cultivar groups can be the cause for bitterness.

For example, the Chinese lettuce cultivar group is well-known for its bitter and robust flavor which is well-suited for stews and stir-frying. This is in contrast to butterhead lettuce which is commonly known for its “buttery” flavor. Head lettuce is a cultivar aimed at removing bitterness in the taste but with the compromise of being less flavourful and nutritional.

A South Korean study showed that genetic variation between cultivars contributes greatly to how they taste and, more importantly, how bitter they are. It was revealed lactucopicrin was the primary contributor to bitterness and that cultivars with greater concentrations of said compound in the leaves are consistently more bitter.

Some cultivars have been specifically bred to remove or lessen bitterness in the leaves. In general, these cultivars are less nutritionally dense, have higher water content, and exhibit a lighter shade of green.

Solution

Cultivars such as the Chinese lettuce should be avoided if a mild bitterness is not preferred. Summer Crisp, Romaine, Looseleaf, and Butterhead lettuce cultivar groups are not known to be bitter and would be a better cultivar group.

However, given that there will still be genetic variation in and between cultivars, it is hard to conclusively say whether lettuce will taste bitter because there might be genetic outliers. It’s a good idea to grow a sample batch to see if they exhibit a flavor consistent with their cultivar group before growing them en masse.

5 – Improper Storage

Improper storage of lettuce can significantly affect the taste of lettuce. Lettuce will become bitter and tough if improperly stored.

Improper storage of lettuce can cause the decomposition process to go faster, making it less crisp and flavourful. Old lettuce is wilted, slimy, sour, and odorous.

Solution

Lettuce should be washed, stored, dried, placed in an enclosed container or a plastic bag, and finally placed in a refrigerator. Lettuce is said to keep best at 32°F (0°C)and 96% humidity according to the University of Illinois. Refrigeration for 2-3 days is said to alleviate the bitterness in lettuce.

It is best to consume lettuce within 7-10 days from purchase to maintain freshness and taste. However, head lettuce can last longer for around 1-3 weeks.

It is also not recommended to store lettuce with fruits such as apples and bananas as these fruits release ethylene gas which catalyzes the ripening and spoiling process. Keep lettuce separate from fruits.

6 – Supertasters (You!)

It might not be the lettuce that is the problem, but you!

Supertasters are individuals who have greater sensitivity to taste compared to the average person. Studies have shown that supertasters have increased sensitivity to bitter tastes. Supertasters can be a result of either genetics or selective eating habits.

So it might not be that the lettuce tastes strongly bitter but that you are tasting the bitterness with greater sensitivity and intensity than most people.

Solution

Sorry to disappoint you, but being a supertaster has no solution. It’s either a product of genetics or selective eating habits which are factors that are difficult or impossible to change in the present.

The best workaround is to properly season and create dishes with lettuce that would downplay the bitterness by putting to the forefront other flavours.

Exciting Lettuce-Based Recipes

Lettuce sometimes has the notoriety as the boring and unexciting component in an otherwise healthy salad dish. This doesn’t have to be this way!

Experimentation with different lettuce cultivars can create a range of dishes which satisfies the heart, mind, and belly. The feeling of being sated is not wholly reliant on whether your stomach feels full but also if your mouth feels that it consumed good food.

Never deny yourself the pleasure of a good, flavourful meal.

One of my favourites is in Asian cuisine with the Vietnamese Pork Lettuce Wraps. It uses lettuce as the all-important holder to pork, sauce, and grated vegetables, and peanuts. It’s nutritious, low on carbs, but still delicious.

Here’s a short video to show how to make it!

Vietnamese-Flavored Grilled Pork Lettuce Wraps with Grated Vegetables and Peanuts

The wide availability of lettuce in markets has created various lettuce-based dishes inspired by exciting culinary traditions – Asian, Italian, Middle-Eastern, and others. Go out and try them yourselves!

Takeaways

  1. Hydroponics lettuce should taste the same as soil-cultivated lettuce. There is no significant difference between the two except that hydroponically grown lettuce should grow faster and should be more nutritionally dense.
  2. Reasons for bitterness that can be addressed are 1) too much nutrients, 2) high calcium content, 3) growing in the summer heat, 4) the lettuce cultivar, 5) improper storage. These can be addressed by flushing, growing during the colder seasons, choosing the right cultivar, and proper storage.
  3. Reasons for bitterness which cannot be addressed are due to supertasters. This is because the issue is inherent on the taster and not the lettuce.

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Andrea

A young Italian guy with a passion for growing edible herbs. After moving to the UK 6 years ago in a tiny flat, it was impossible to grow herbs outside. So I start my journey in growing indoor and so I decided to share my knowledge.

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