Why Are Your Hydroponic Plants Dying? 5 Common Reasons


With rising housing costs, and storage space coming at a premium, hydroponics has quickly become one of the most popular plant-growing approaches. However, it can sometimes be quite frustrating for newcomers and veterans alike when your plants do poorly. If you’re wondering why your hydroponic plants are dying, this guide will take you through everything you’ll need to know.

The reason why your hydroponic plants are dying is usually connected to poor nutritional or environmental conditions. These issues generally include problems with the nutrient solution (e.g., unstable pH and oxygen levels) or circumstantial inadequacies like pests and poor lighting.

However, there’s a significantly wider range of factors that could negatively affect your plants’ longevity, so keep reading if you’d like to learn more about each problem and, more importantly, how to fix them.

5 Common Reasons Why Your Plants Are Dying

While in broader terms, you can categorize the life-threatening issues your plants face as either solution-based or environmental; the actual complications are a lot more specific. Therefore, it’s crucial to understand each problem and how to solve it if you want to keep your plants alive. 

Here are some reasons why your hydroponic plants are dying:

  1. The water pH is unbalanced.
  2. Lighting levels are sub-optimal.
  3. There’s not enough oxygen.
  4. Pests are attacking your plants.
  5. Your plants are suffering from nutrient deficiency/toxicity.

This list is by no means exhaustive, but it covers most of the common reasons why your plants could be dying.

1. The Water pH Is Unbalanced

Water pH is one of the most common causes of dying plants in hydroponics. Although the absence of soil is one of the discipline’s main attractions, it unfortunately also has its downsides.

Using water comes with a host of potential problems. For this reason, you’ll constantly have to maintain its pH at an optimal level to ensure your system works efficiently. 

One major cause that changes water pH is that nutrient solutions do not have CEC (Cation Exchange Capacity). In soils, this refers to the ability of a sample to hold cations that can be readily exchanged with its surroundings. 

CEC works like a buffer solution. The chemistry behind it is a little complicated, but the key takeaway is that it provides some protection from drastic changes in pH.

Since soil and, by extension, CEC is absent from most hydroponic systems, there is very little protection against changes in acidity levels. 

However, rather than thinking of CEC as a single problem, it’s better to consider it a lack of protection against multiple factors. Ideally, small changes in pH shouldn’t affect the plant by much, but because CEC is absent, many issues can begin to surface. 

Some of these issues include:

  • Disease
  • Temperature
  • Water type 
  • Water quality, etc.

Treating pH deficiencies is a problem that has to be tackled on its own, outside of its sympoms. The best way to solve your pH is to test the water in your hydroponic system regularly with a pH meter. 

These meters are usually cheap, widely available, and easy to use. Alternatively, you can make use of testing strips to check your pH. Regardless of the method you choose, it’s important to make checking your water pH a regular habit. Daily or weekly checks will keep you ready to tackle any problem that arises. 

If you want to keep your plants in the best shape possible, your water pH should be within the 5.5-6.5 range. 

If your water is too acidic (pH less than 5.5), you need to make it more alkaline. You can do this by adding baking soda a little at a time until the solution reaches its optimal pH.

On the other hand, if your water is too alkaline (pH more than 6.5), you need to make it more acidic. The best way to do this at home is to add some lime juice a few drops a time until it reaches the optimal pH.

If you’re producing on a large scale, lime juice can be expensive to come by in the quantity you need. In this case, citric acid is a better alternative. 

2. Lighting Levels Are Sub-Optimal

Light is extremely important for plant growth. Without sufficient lighting, plants will usually start to change in color. This color change can be as mild as pale green and as extreme as white. If the light deficiency gets bad enough, it’s common for plants to eventually die.

To avoid lighting-related problems, it’s crucial to expose your plants to the necessary levels of brightness required by them to thrive. A popular misconception is that you need to leave your plants with as much light as possible. This view is only true for some plants.

There are three different types of lighting that a plant might need:

  • Short periods: Plants that fall under this category need less than 12 hours of light per day. Light is still important for them, but they also need long periods of darkness to photosynthesize properly. This feature is prominent in plants that do best in spring or similar seasons, depending on your location. Examples are strawberries and chrysanthemums.
  • Long periods: Long-period plants require up to 18 hours of light each day to thrive. These plants do well in the summer when there is maximum exposure to sunlight. Examples include plants like potatoes and wheat.
  • Neutral: Neutral plants are not particular about excessive lighting. It’s important to understand that these plants still need light. They just don’t mind getting more than they need. A good example is the rice crop which requires at least 6-8 hours of lighting each day to grow properly. You can even expose it to higher brightness levels for longer than that with minimal repercussions, but you must give it the required amount of light.

Along with the light exposure required, its intensity and wavelength are also important. Not all light varieties are the same, and the conventional bulbs you use at home cannot give you the results you want with hydroponics. 

The best solution to your lighting problems is to use grow lights. There’s a variety of guides online about different types of lighting and their benefits, but the reality is that grow lights outperform them all.

Grow lights are a form of led light made specifically for plant life. Rather than relying on picking the right lighting intensity in your fluorescent bulb, grow lights come with variable intensities and wavelengths, so you can tune each feature to your needs. 

Barrina BU 2000 LED Grow Light (available on Amazon.com) is an excellent choice. It comes with a full LED light panel, and with an estimated run-time of 3000 hours, so you’ll rarely have to worry about replacing it.

3. There’s Not Enough Oxygen

Oxygen is a crucial substance for any living species, plants included. Oxygen molecules are even a major part of water, and plants need this to thrive. 

However, even though the oxygen plants retrieve from water is important, dissolved oxygen molecules are arguably even more necessary. Low levels of dissolved oxygen can be incredibly damaging for your plants.

The problem with dissolved oxygen is two-fold. First, aerobic bacteria exist in the rhizosphere (the area around your crop’s roots). These bacteria are beneficial for plant roots only thrive when there is enough dissolved oxygen in the solution for them to live. Once oxygen levels drop, they begin to die. 

The death of the bacteria is bad enough on its own, but their death combined with low oxygen levels creates the ideal environment for anaerobic bacteria to grow. These anaerobic bacteria are bad for plants and can cause a wide range of issues.

Optimal oxygen levels are also essential for nutrient uptake, so reduced oxygen in the solution reduces the number of nutrients available for your plants. Plants that lack oxygen will show signs like wilting and droopy, shrunken leaves. 

It’s crucial to perform daily checks regarding dissolved oxygen levels in your system to avoid this problem. The best way to do this is with an oxygen meter, as it gives you very accurate results. 

Ideally, the dissolved oxygen level in your system should be at least 5 mg per liter of solution(mg/L). Anything less than that is a cause for concern and will need to be corrected. However, the only way to properly correct an oxygen deficiency is to get to the root of the problem first.

There are two major reasons why oxygen levels can drop in a hydroponic system:

  • High temperatures
  • Poor aeration

High Temperatures

High temperatures are the enemy of dissolved oxygen. Oxygen is less soluble in liquids at higher temperatures, so the increased temperature of the nutrient solution means that there is less oxygen available for use.

It’s important to maintain temperatures at a suitable level for plants. However, there is no temperature guard with hydroponics as there is with soil-based planting. This absence leads to a problem where higher temperatures make it difficult for your plants to absorb oxygen.

With solid-based plants, the temperature is less of a problem because the topsoil protects plants by insulating the lower layers from the less-than-ideal temperature. This insulation protects the soil’s oxygen content and is a feature that is sorely missing from hydroponics.

Since hydroponics uses a solution to grow, its plants can be a lot more sensitive to changes in temperature. Due to this temperature sensitivity, you’ll have to pay constant attention to the ambient and water temperatures. 

If you have an indoor system, ambient temperature is usually easily identifiable. Any temperature that would cause plants to lose oxygen would be uncomfortable enough for you to feel, making it much easier to detect and adjust to the proper level. 

On the other hand, if you have an outdoor system or leave your plants in direct sunlight, temperatures can rise to the point where they reduce oxygen levels without you noticing.

The solution to ambient temperature problems is to try as much as possible to regulate the room’s temperature. If the system is outdoors or in direct sunlight, you might need to control the temperature of the water with a water chiller. 

Alternatively, you can also use an air conditioner to reduce a room’s temperature.

Poor Aeration 

The second problem is poor aeration. Since plants are constantly using up the oxygen available in the solution, it’s crucial to replenish the consumed resources through aeration.

Aerators come in many forms, but the airstone is the most popular by far. Airstones are perforated rocks attached to air pumps. The pump passes air through to the stone, and the holes in it cause air to distribute evenly through the water. 

4. Pests Are Attacking Your Plants

Thankfully, pests are not as big of a problem in hydroponics (especially indoor hydroponics) as in soil-based horticulture. The spaces around hydroponic systems are usually enclosed, and because of this, the amount of pests that can reach your plants is significantly reduced. 

However, ‘few’ is not the same as ‘none,’ and there are a few pests you should be wary of in hydroponics. These are some of the most common ones:

  • Aphids
  • Spider mites
  • Thrips 

Aphids

Aphids are not the most common hydroponic pest, but they are among the most damaging. Aphids come in various colors, but the most common ones are usually green or back and wingless.

They are extremely disruptive and cause various direct and indirect issues to your plants. The primary problem they cause is the way they weaken plants by sucking the sap from them. The sap is essentially the equivalent of blood to plants as it carries nutrients all over the plants, so an uncontrolled aphid presence will eventually kill your plants.

Along with sucking up the sap from your plants, aphids are also the vectors for various diseases in plants. Because of this, aphid presence can quickly decimate your entire system by transferring diseases from one plant to another.

Aphids reproduce rapidly, so you need to act as fast as possible to prevent an outbreak once you detect them. An aphid outbreak is deadly to plants and, if not properly managed, could be the end of your hydroponic system. 

Insecticides are one way to control aphids, but even strong insecticides can be less effective than they should. Because Aphids reproduce so quickly, if you miss even a couple, they can repopulate very quickly. 

If you use insecticide, you will need multiple sprays over a few days to ensure that you get them all. Also, when you spray, try to get as many of them as you can by spraying corners, undersides of leaves, and anywhere else a stray aphid might be hidden.

Aphids are usually outdoor insects, so it’s important to ensure that you don’t transfer them into the house from outside, as this is one of the most common ways they get into your hydroponic system in the first place. 

Avoid using the same tools for both outdoor and indoor work. If you must use them, make sure they are properly cleaned.

Spider Mites

Spider mites look similar to spiders since they are from the same arachnid family but are significantly smaller. They vary in color, but they make their presence known by leaving yellow spots on the leaves. 

These yellow spots form when the spider mites feed on the plant by piercing leaves and sucking up nutrients from it. With time and continued feeding, entire leaves begin to yellow completely and dry until the plant eventually dies. 

Another sign of spider mites is webbing on the leaves of plants in your hydroponic system. However, this is usually an advanced symptom, and it’s best to catch them before it gets to this point. 

Regardless of the detection method, once you suspect the presence of spider mites in your system, you must take action immediately. The first thing I would recommend doing is to confirm their presence. The best way to do this is to check the underside of your leaves. 

Spider mites are extremely small and hard to see with a naked eye; however, if you put a piece of paper beneath a suspected leaf and shake it, the mites become dislodged and appear on the paper as rust-colored, oval-shaped dots. 

Once you confirm their presence, you can start taking steps to cull them. Unlike many other insects, insecticide only works on mite populations for short periods. Mites reproduce extremely quickly, so successive generations easily build up a tolerance to harmful chemicals. 

As a result, insecticide is usually only a good solution if you catch the infestation early enough to stop it.

If this isn’t possible, then the next best thing you can do is introducing a controlling biological population like ladybugs that will prey on the mites. 

Another option is to quarantine affected plants and remove leaves that have been damaged. This step on its own will not eradicate the population, but it will help reduce the infected population and make any other method you use more effective.

The best preventive measure against spider mites is humidity. They thrive in dry conditions, so increasing moisture levels around your plants with a humidifier is an excellent option.

Thrips

Thrips are an extremely destructive species of winged insects. Like spider mites, they damage plants by sucking up nutrients for them, but while mites are usually found on leaves, thrips can be found on every part of the plant. 

If that wasn’t enough, thrips are also vectors and carry a range of viruses that can worsen the problem. The damage they do to plants makes them vulnerable to bacteria and diseases.

Thrips cause extensive damage to any hydroponic system; therefore, controlling them is crucial. Like spider mites, the reproductive rate of thrips makes it difficult for most types of insecticides to be effective. To further compound the problem, normal biological control is also less effective due to thrips’ speeds and size.

The best option is to use biological insecticides or insecticidal soap to control a thrip population. Research also suggests that red light can reduce thrip presence, which could be an option if you’ve invested in grow lights.

5. Your Plants Are Suffering From Nutrient Deficiency/Toxicity

Sometimes your plants simply aren’t getting enough nutrients. This problem can occur for various reasons, but it’s usually easy enough to identify once you know the symptoms.

Since plants rely on a wide array of nutrients to survive, nutrient deficiencies are not uniform, as the absence of each specific nutrient can cause a different problem. These are the major nutrient deficiencies and their symptoms:

  • Nitrogen: Nitrogen deficiency affects the plant’s ability to produce energy for itself, as the substance is the central part of the Nitrogen Cycle. Its deficiency shows in the form of paleness in leaves(chlorosis), stunted growth, and wilted leaves.
  • Phosphorous: Phosphorus deficiency usually causes plant leaves to darken and flower size to reduce. Leaves also take on a dark red or purplish hue.
  • Potassium: Potassium is responsible for protein synthesis in plants, and its absence leads to stunted growth in plants. It also causes chlorosis, especially in the plant’s veins, along with the browning and curling of leaves.

These are the most common (and dangerous) nutrient deficiencies, but there are 14 other micronutrients whose presence can significantly impact a plant’s longevity, and the National Park website does a great job of identifying and categorizing all of them.

Now that you can identify nutrient deficiencies, the next step is to learn their causes and how to solve them. 

Here are a few of the most common causes of nutrient deficiency:

  • Plants: Nutrients are used up by plants over time, so it’s important to replenish them when their levels get too low. The main solution to the problem is to change the nutrient solution in your system frequently. 
  • pH: The pH level directly correlates to the availability of many key nutrients in the solution. The pH indicates acidity and alkalinity levels, and the optimal range should be between 5.5-6.5. If your pH is outside this range, you should raise or lower it using the steps mentioned earlier. You can also use a buffer solution to reduce pH fluctuations.
  • Temperature: Temperature can catalyze reactions in your solution or cause some nutrients to precipitate. Once they precipitate from the water, they are unusable for plants. You have to consistently keep your plants within optimal temperatures to correct this issue.

A good overall tip to combat nutrient deficiency in plants is to make sure that your nutrient solution is always mixed in the right proportions. If there is an imbalance in the amount of nutrients available in the solution, it can cause deficiencies and toxicity.

Toxicity is the exact opposite of deficiency. It happens when you have too much of one or more nutrients in your solution and share similar symptoms to nutrient deficiency.

A good way to differentiate between both of them is to check the electrical conductivity of your solution. Electrical conductivity uses how well the solution conducts electricity to give you an idea of the dissolved nutrient level in the water. For most plants, the optimal level lies in the 1.0-2.5 s/m (siemens per meter) range. 

If your conductivity is too high, diluting the solution with distilled water will correct it. Alternatively, if it’s too low, then you’ll need to increase it by adding more nutrients to the solution.

Final Thoughts

Hydroponic problems are either nutrient-related or environmental. It’s crucial to efficiently identify each type of problem and know how to deal with it adequately to optimize your plants’ longevity.

Above all, make sure you regularly monitor conditions like pH, dissolved oxygen, and physical appearance to ensure that you detect any possible issue as soon as possible.

Alexander Picot

Alexander Picot is the principal creator of TheGrowingLeaf.com, a website dedicated to gardening tips. Inspired by his mother’s love of gardening, Alex has a passion for taking care of plants and turning backyards into feel-good places and loves to share his experience with the rest of the world.

Recent Posts