Why Is My Hydroponic Lettuce Bitter?

Bitter Lettuce

Lettuce is one of the easiest things to grow in hydroponics. You have taken up the challenge and nurtured your seeds into germination and transferred them to your hydroponics system. You have your first harvest washed and sitting in the salad bowl, but something isn’t right.

Why is my hydroponic lettuce bitter? Lettuce might be one of the easiest things to grow hydroponically. However, if you have either a nutrient-rich solution, a growing environment which is too hot, or your lighting setup isn’t at its most optimum, you will get bitter lettuce.

Do you want to grow lettuce which is full of flavor and has no aftertaste? Do you want to know what is causing it, what you can do to resolve the problem, and is it too late to save your current batch of lettuce? Find out with the answers to the questions below.

Why Does my Hydroponic Lettuce Taste Bitter?

With Hydroponics, you have full control over growing conditions, and because of this, it means there are no outside influences so you can narrow down where to start looking. The first area to check will be your nutrients.

Lettuce doesn’t require too many nutrients to flourish. So, if your mix is too rich, it can lead to the bitter taste you have experienced. Although flushing your system is not vital to grow tasty lettuce, it can help improve flavor and remove the bitter taste.

System flushing can be more critical in ebb and flow systems. These continually fill with nutrient-rich water, and then once they drain they begin to dry out. It is during the drying process when mineral salts and nitrates start sticking to everything, including the roots of your lettuce. Veteran hydroponic growers recommend flushing a system before harvesting, even though it isn’t necessary.

Flushing the Hydroponic System

It is these nitrates and mineral salts which can be the most significant cause of bitter tasting lettuce. Flushing depends on the type of hydroponic system you are using. The first thing to do is drain all the nutrient solutions from your tank. Once you have emptied the system, you then need to proceed by rinsing your tanks and hoses with plain water.

If you have a nitrate-rich nutrient mix, you will need to rinse the system two or three times. Once done, you then need to adjust your pH levels to 6.0. Both pH Up and Down plus a Testing Kit can be found online from Walmart, or they will be available from your local hydroponic supplier.

Now, you should leave your system to run for a few hours. If it is the last flush before your lettuce harvest, you can let the plain water run through your system for up to one week.

After doing this, you need to drain the system again and thoroughly rinse your hoses. You should also flush the sides of your tank and check for any buildup or debris. If there is debris, or your system doesn’t appear to be as clean as it should. Then fill the system with your pH adjusted water, rerun your system for a couple of hours, and then finally drain the system.

Any algae or nitrate buildup needs removing, and all sides of the tank wiped. Hoses need cleaning inside, as far as you can reach. Once done, mix a new batch of your nutrient solution while checking it isn’t too rich for your lettuce. Once done, refill your system and let it run.

Items for Flushing the System

Here are some of the things you will need when you flush your system.

Heat Can Cause Lettuce to Taste Bitter

Lettuce is a cool weather plant. If the air temperature rises over 75F (24°C), your lettuce begins producing chemicals for flowering and producing seeds. It is this which can be one of the causes of for the bitter taste depending on the location of your hydroponics system and your region. This will determine how you can control the temperature of your growing environment.

To be accurate in your temps, it is worth investing in a Digital Hygrometer Indoor Thermometer. You can then periodically check your temperatures and humidity. If you are growing inside a greenhouse, there is one mistake many people make, and that is to shade the plants. Shading, unfortunately, isn’t the answer and you should be looking at ventilation or a form of cooling.

Evaporative cooling is the best option and can be from either a fan and wet-pads system, a low-pressure misting system or high-pressure fog system. All these should be used in conjunction with mechanical or natural ventilation. As a last resort a shade curtain can be used, but for no more than up to four hours and only during the hottest part of the day.

Incorrect Lighting Can Make Lettuce Bolt and Taste Bitter

If you are growing indoors and using artificial lighting, then things can be easier to control. Generated heat comes from your lighting, and the worst culprits being HID (High-Intensity Discharge) growing lights. You can help combat this if you see the overall room temperature is increasing.

You can place your lights inside an air-cooled reflector where the coolest air possible is ducted to the reflector, and then vents from inside your room via insulted ducting to prevent heat transferring back inside and affecting the ambient temperature.

You have seen, heat generated from grow lights raises the temperature of indoor grow rooms. There are three basic elements included in this section. One, the lights are not the best type and produce too much heat. Two, the length of time your grow lights are turned on is too long, and there is little or no adjustment of lights when required. Finally, the best bulb or tube type isn’t being used.

The positioning of lights can be the quickest variable to resolve, and no matter what artificial lighting method you are using, light sources should be around 4-6 inches above your plants. As they grow, the distance needs adjusting to maintain this gap. Because lettuce is a fast grower, it is crucial to keep a constant check on their progress so you can manage the optimum growing distance.

Light Quality Affects the taste of Lettuce

For lettuce to grow successfully, it requires a minimum of 12 hours of light. The ideal amount of light for most plants is 14 – 16 hours. If your growing location makes use of natural light, this needs to be used in your calculation for how long you will be using grow lights. Winter time has fewer sunlight hours, and this means you will be using your grow lights for longer. If you either leave them on too long or even forget to turn them on at the correct time, it plays havoc with your plants growing schedule.

The final element is the type of grow lights you are using. There are a few types to choose, and these include LED grow panels, HID lamps and Fluorescent tubes. LED’s are finally catching up and require further discussion which leaves HID and Fluorescent.

HID grow lights are the lighting type which generates lots of heat. These are recommended for more experienced users and are the lighting types which require cooling. Fluorescent tubes are more suited to growing lettuce because they run much cooler, but even differences in these lighting tubes can affect the growth of lettuce.

T5 fluorescent tubes are the best choice over T8 or T12 tubes, even though they require different fittings. They also give off more heat than these other varieties, but allowing for this, it is the Kelvin rating which can be a reason you are finding bitter tasting lettuce.

T5 fluorescent grow lights are the most efficient of all fluorescent tubes. However, tubes with a 6500 Kelvin rating deliver a full spectrum of light, which is excellent for overall growth. Lighting tubes with a 3000 Kelvin rating produce more red spectrum light which helps encourage flowering or bolting too early.

Related Questions

How Can I Get the Bitter Taste Out of Leaf Lettuce?

It can help to separate the leaves and put them in a bowl of cold water with a pinch of baking soda. Soak for ten minutes, rinse and soak again in plain water. Drain and serve. You can also use a salad crisper, or place the lettuce leaves in the refrigerator overnight.

What is the best lettuce variety to grow hydroponically?

Many growers choose leaf lettuce (Lactuca Sativa) along with the Tom Thumb variety. The Tom Thumb variety is easy to handle and grows large enough for one head to be enough for two people. Romaine lettuce, on the other hand, takes longer to mature, so it could be more prone to becoming bitter.

How long does hydroponic lettuce take to grow?

Nearly all varieties of lettuce can be grown in a hydroponic system. Leafy lettuce varieties are the recommendation because they can grow to harvest in half the time of head varieties of lettuce. When conditions are right, you can expect to be harvesting lettuce in three to four weeks.

How Often Do You Change Water for Hydroponics?

Changing Water

If you’re just getting into hydroponics, or you just want to make sure your plants are healthy, you need to maintain your water system. A big part of that is making sure you have appropriate nutrients, pH level, and clean water.

How often do you change water for hydroponics? A general rule of thumb is that hydroponic water should be changed out every two to three weeks. Depending on your system you may change it more or less often to maintain optimal pH and nutrient levels.

The frequency with which you change your hydroponic water is important, but so is how you change it. In fact, the timing of the of the water changes is more complex than simply dumping and replacing the water bi-weekly.

How your set up affects frequency of water changes

How frequently you need to change your hydroponic water can also be affected by the specifics of your set up. Your water reservoir will inevitably lose some water volume due to evaporation and plant use.

You’ll lose more water due to evaporation if your set up has a lot of light and heat. This is even more so if there’s not sufficient coverage on your reservoir, or if your reservoir is placed relatively close to light and heat sources. Likewise, if you have a high plant density or plants that use more water, you’ll lose water faster. So if you plan on growing something like irises, lettuce, or spinach, you’ll need to add water more frequently.

Smaller water reservoirs need to be topped off with fresh water more frequently than larger reservoirs. We’ve written a complete guide to water tanks with size estimation along with everything we think you need to know.

In most cases, you’ll need to add water to your hydroponics in between water changes. If you have a fair amount of water loss, plan on topping up the water as frequently as daily. If you don’t notice much difference in the water level from day to day, plan on topping up the water every few days. Every two to three weeks you will have to change out more water. Once you’re more familiar with your hydroponics system you’ll be able to develop a steady routine for topping up the water and doing partial water changes on a schedule.

How to change out your hydroponic water

When you change out your hydroponic water, you’ll be doing it in two ways. It’s important to use both ways of replacing water, and to do both regularly. We’ll cover more about the reasons for this later but for now, you need to know what the two methods are and how to do them.

The first kind of “water change” is when you top off your water reservoir. When you notice your water getting lower, you need to top it off. The best way to do this is using pH balanced, clean water. You will end up adding water several times weekly, if not daily. When you top off the water, be sure to measure and log the amount of water you add. You’ll need these logs later to help determine when to do a bigger water change.

The second type of water change is much less frequent, and switches out a much larger volume of water. Once your logs show that you’ve added about half of your total reservoir volume by doing top ups, you need to do a larger water change.

To do this, empty or drain 50% the total volume and replace it with fresh water (example: if your reservoir holds 100 liters, and over a couple weeks your logs show you’ve added 50 liters by topping up the water, it’s time for you to take out 50 liters and add the same amount clean, pH balanced water). Most hydroponic systems need this larger water change as frequently as every two weeks, although smaller reservoirs may need it as often as every week to ten days.

Water changes to manage pH and nutrients

Maintaining your pH level and making sure you provide your plants with enough nutrients is part of the reason that regular water changes are so important. Over time, the pH of your water will change. If your pH isn’t in the acceptable range for your plants, they won’t be able to absorb any of the nutrients you’ve added to the water. If you aren’t sure how to check the pH of your water you can read our full guide here.

Only changing out the water in its entirety isn’t ideal for your plants. First, because other compounds, such as ammonia or nitrites, can accumulate to harmful levels that ultimately kill your plants. Second, without an infusion of fresh water, the water in your reservoir can become a stagnant haven for bacteria and fungi. That, combined with roots made susceptible by chemical damage, creates an ideal situation for root rot to move in. If you aren’t sure about the best ways to prevent and treat root rot then we’ve written a guide for you here.

The most important reason you need regular water changes to maintain pH, rather than a single and infrequent water change, is to prevent shock to your plants. Regularly adding clean water, in between bi weekly water changes allows you to maintain a steady pH level.  Sudden, drastic changes in water conditions (like what happens when water is completely changed) can cause more harm than benefits to plants.

Managing nutrient saturation

While water changes help when you’re adding nutrients, they also help prevent damage to plants from over saturation of minerals. When nutrients are used by plants there are still traces of minerals and compounds left behind. Plants use up more water volume than they do nutrients, which creates a situation where nutrients are more saturated than when you first added them. Too much of these leftover trace minerals can burn plant roots or kill your plants. So if you’re not sure if your nutrient levels are helping or harming, always test for it.

Testing to determine water changes

There are situations where you’ll need to change water more or less frequently than you usually would. This switch in water change routine is typically a response to correct harmful conditions for plants. With regular testing, you can monitor the water quality of your reservoir and correct problems before they become urgent.

Different types of testing

There are two main types of water testing you need to be familiar with to properly maintain your hydroponic water. There are other more in depth tests you can use for your water, but for the average hydroponic gardener pH and EC testing are more than sufficient.

pH testing

pH tests help monitor the pH, or potential hydrogen, levels of your water. For most plants the ideal pH is between the range of 5.5 to 6.5. While this fluctuates slightly between water cycles, it shouldn’t change drastically. You should test your pH every three days or so, unless you notice your plants showing signs of wilting, illness, damage or discoloration. pH test kits can be purchased in either paper strip or liquid solution form. Now, digital pH testing pens are being used more frequently due to their convenience and accuracy.

EC testing

EC testing, also known as electrical conductivity testing, will help you monitor and maintain the strength of your hydroponic nutrient solutions. While your ideal EC level will vary depending on your chosen crop, most plants thrive at levels between 1.2 to 2.0. If your EC is below that, you know you need to add more nutrients to your water. Likewise, if your EC level is too high, you need to add in clean water to dilute the solution. In extreme cases, you may have to remove some water and replace it with fresh water, gradually lowering the level over several days. The most common EC testing method uses a digital pen, and some testing pens can test for both EC and pH. Some people test daily until they’re more familiar with their water levels. At the very least you should be testing EC levels every three days (when you test your pH), and every time you add nutrient solution. We’ve got a comprehensive guide to testing the EC in water if you aren’t sure.

Related Questions

How often do I need to clean out my water reservoir?

Much like with water changes, this can vary depending on your set up. Smaller reservoirs require more frequent cleaning. A good rule of thumb to follow is this: once the water you’ve been replacing or topping up with equals your total tank capacity, it’s time to clean it out.

Do I need to add extra aeration to my hydroponics system?

Using an air pump or stone isn’t required for every hydroponics setup. However, if your plants’ roots are fully submerged, it’s a safe bet to oxygenate your water. This not only keeps plants from “drowning” without oxygen, but also helps inhibit the growth of bacteria, algae, and fungi, thus reducing plant disease.

Is It Safe to Buy Hydroponic Gardening Equipment Online?

Hydroponic Equipment Online

Over half of all purchases made annually are made online.  E-Commerce is a huge industry and most people don’t give shopping online a second thought.  But what if you are purchasing items that could be misinterpreted as questionable (read: illegal) activity?

Is it safe to buy hydroponic gardening equipment online? Yes, it is perfectly safe to buy hydroponic gardening equipment online, as long as you buy from reputable websites and take precautions to protect yourself from identity theft.

Several online stores – particularly those specializing in home improvement, such as Home Depot – have dedicated sub-menus specifically for hydroponic equipment.

Hydroponics 101

In ultra-simple terms, hydroponics is gardening without the soil.  A more complex explanation is hydroponics is a method of growing plants in a soil-free nutrient solution.  Perlite, rockwool, clay pellets or peat moss are used as an alternative to soil.

Hydroponic gardening allows the plants to have access to direct oxygen and nutrients without the bugs and cold weather worries.  If you provide proper light and water, hydroponic plants can grow 30-50 percent faster. (Information courtesy of Greentrees Hydroponics)

There are a variety of hydroponic systems available to purchase.  The systems are either active or passive. An active system is the preferred method because they are more effective in moving the nutrient solutions throughout the plants, usually via a pump. A passive system relies on a wick or medium to pass along the absorbed nutrients onto the roots.  (“Medium” refers to the materials used to make the plants grow.)

Types of Hydroponic Systems

  • Wick System

The simplest and least expensive system, the Wick System uses the candle wick to absorb the nutrients into the growing medium.

  • Water Culture

Comprised of a styrofoam platform that holds the plants, the platform floats directly over the nutrient solution, providing water to the roots.  Leaf lettuce is the only plant that works well with this system, making it popular among elementary school teachers.

  • Nutrient Film Technique System

In the Nutrient Film Technique (NFT) System, plants are placed in net pots, which are then partially submerged in a channel that hovers above the main reservoir.  The channel has a constant flow of nutrient solution running across the bottom of the channel (the “film” part of the name) that drains into the larger reservoir.

  • Aeroponic System

The Aeroponic System is considered the highest tech of the different systems.  The plants are suspended from the air in a basket and misted with the nutrient solution.  The misting occurs at preset intervals that can be adjusted to your liking.

The Ebb And Flow System drench the plants in the nutrients and then drains the solution into the reservoir via a pump with a timer.

  • Continuous Drip System

Perhaps the most popular system, the Continuous Drip System utilizes a timer-controlled pump that trips the necessary nutrients onto the plants.

Online Vs. In-Store Purchasing

When considering the merits of online shopping against in-store shopping, it is important to keep in mind convenience, customer service, warranties and returns/exchanges.

The biggest advantage of online shopping is the convenience of not having to find a parking spot, brushing your hair or fighting the crowds.  Shopping online is virtually hassle-free. You can purchase your item with the click of your mouse instead of waiting in long check-out lines for the next available register.

While good or bad Customer Service is a reflection on the store itself, it is ultimately the responsibility of the Customer Service employee as to whether your experience is excellent or poor.

Online Customer Service is a fantastic option if you prefer not to deal with people face-to-face.  However, that lack of human interaction can lead to a feeling of impersonality and lead to miscommunications and misunderstandings.

Many retailers offer free or low-cost shipping options when it comes time for your order to be delivered.  More and more stores now offer in-store pick-up, where you order online and if a local store has it in stock, you can go there to pick it up the same day that you order it.  That option is dependent upon whether the store physically has the item on-hand, so it may not be particularly feasible in rural areas. Online retailers also allow you to have the item shipped to your local brick-and-mortar store to pick-up instead of directly to your home or office.  

When you shop for an item online, you are faced with a plethora of merchants available.  It can be difficult to know which ones are real and which are scams. Unless it is a well-known chain-store, proceed with caution.  Do your due diligence and research the stores if they seem the least bit sketchy.

Warranties offer guaranteed protection if the item you purchase breaks or has other issues.  Some companies void warranties if the item is purchased online, so that is important information to weigh when making online purchases. So, again – do your research if you plan to make big-ticket item purchases.

Returning or exchanging an item is easier in-store than it is online.  It is certainly quicker. To return an item online — assuming the company allows returns — you have to fill out the return paper, repackage it and take it to the post office, where it has to be shipped and processed.  Returning an item to an online store could take days or even weeks if you purchased from an overseas company.

When you weigh the pros and cons of online shopping and making your purchases in-store, online shopping is certainly more efficient and convenient.

Tips for Purchasing Hydroponic Gardening Equipment Online

Any purchase online is a gamble.  Websites can be susceptible to hacking and your information being stolen.  If you purchase online, your credit card information can be readily available if the website is hacked.  Some websites also sell the addresses and phone numbers of their customers to other companies. While that isn’t likely to affect your credit card, being inundated with unwanted phone calls and junk mail can be an inconvenience.

Another potential option in online shopping is to buy your equipment through eBay or Craigslist.  eBay is a legitimate wholesaler that also allows users to sell items secondhand.

Craigslist is a bit trickier, though.  Like eBay, it allows its users to post items for sale, but there’s no oversight regarding the quality of the merchandise.   It’s akin to a giant internet garage sale. Unless you’re up for a long drive, items are usually purchased locally and picked-up in person.  Money is typically exchanged during the pick-up and it can be a dangerous situation. The best thing to do when using Craigslist is to have a friend go with you to pick-up the item you’ve purchased.  

Related Questions

Is it illegal to own hydroponic equipment?

The short answer to this question is no.  The longer answer is much more complex and depends what you want to grow, as the topic of legalizing marijuana has drawn a lot of undue attention to hydroponic equipment sellers.  Some states in the US are taking steps to legalize cannabis for medical use and recreational use. Other states are taking the opposite stand and cracking down on marijuana offenses.

What is a grow shop?

A grow shop is a retail store that sells hydroponic and other supplies for growing plants indoors.  Unlike merchants that sell a variety of inventory, grow shops are dedicated solely to the booming indoor growing niche. The store can be an online business or a brick-or-mortar store.

What Can You Grow With Hydroponics?

If you can grow it in an outdoor garden, the chances are that you can grow it in an indoor greenhouse as well.  Rooting, stalking and vines crops (such as potatoes) can be difficult because they require more depth for growing.  

Herbs, salad greens and vegetables are among the most popular choices in hydroponic growing.  Flowers grow well, too. Some flower ideas are marigolds, carnations, roses and even sunflowers.

What Are The Benefits to Hydroponic Gardening?

Gardening is a hobby enjoyed by people in many countries around the world.  Most people think of garden as being outdoors, but there are many benefits to indoor gardening:

  • Indoor and outdoor growing year-round

Not all climates are friendly to outdoor gardening.  Hydroponic gardening allows people to grow their plants indoors during the colder months and transfer them outside in the warmer months if desired.

  • Saves water and damage to soil

Plants grown using the hydroponic system get their food from water and nutrient solutions instead of soil.  Many systems have recycling water systems.

  • Plants grow faster

It is proven that hydroponic plants grow 30-50 percent faster with higher yields.

  • No pests or weeding necessary

Growing indoors prevents plant-killing pests from infecting the plants.