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6 Reasons Why Lettuce Grows Slowly in Hydroponics

Hi friends, I have been growing lettuce on hydroponics for quite some time and today I want to discuss an important topic. Many people ask me why lettuce sometimes grows slowly on hydroponics.

From the start, the lettuce seedlings are quite vigorous, but after a few days they slow down. Sometimes it seems that they don’t grow at all, but in fact they only grow slowly. This is how young plants gain strength and in about the third week of life they start to grow very quickly and reach their maximum size in 7-10 days.

It follows that if your lettuce is still young, you have nothing to worry about. After a while it will accelerate its growth. However, if the lettuce has not yet grown to its normal size in a month, then something else is stunting its growth. You will learn about all the possible causes in this article.

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Water pH

The first thing you need to pay attention to is the pH of the water. This is crucial because if it is too high, the lettuce will not be able to consume the plant’s food and will slow down its growth.

Other symptoms can be yellowing of the leaves or browning of the tips.

Lettuce needs water that has a pH of 5.5-6.5. In this case all nutrients and minerals will be easily absorbed and the plant will grow quickly.


  1. Using a pH meter check the pH of the water in the tank.
  2. If the pH is higher than 6.5, adjust it using a pH reducer.
  3. Always check the water before refilling the tank for pH.

Root problems

hydroponic plants wilted because of root rot

Root Rot

The second cause is root rot. If the roots of the lettuce begin to rot, it will stop growing and the tips of the leaves will turn brown. Rotten roots are unable to provide the plant with water and food and the plant may die as a result.

Root rot is usually caused by dirty water. If the water is not changed, slime will form on the roots, which will lead to root rot.

Root rot can also be caused by poor quality sponges or too high a water temperature in the tank.


  1. Change the water in your hydroponic system at least once a month.
  2. Clean and sanitize all parts of the hydroponic system every time you change the water.
  3. Rinse the roots of the plant under running water every time you clean the system.
  4. Use only quality growing sponges from verified suppliers.
  5. Make sure the water temperature in the tank does not exceed 73.4°F (23°C).

Plant food problem

Without plant food, growing hydroponic plants is impossible. However, not all plant food is equally good. On the market you can find cheap products that work very poorly as feed for hydroponic plants.

Lettuce does not require much nutrition, but poor quality plant food can cause it to grow slowly. For this reason, I recommend using only quality products.

Personally, I use Flora Series from General Hydroponics. In addition I use another product from this company called CALIMAGIC which contains additional calcium and magnesium.


  1. Change the water in the hydroponic system to fresh water.
  2. Adjust the pH if necessary.
  3. Add Flora Series plant food in the amount recommended by the manufacturer.

Not enough light

light issues

The LEDs need to be replaced here.

It is well known that light is the energy that ensures the growth of the plant. If there is not enough light, the lettuce can become elongated and stunt its growth.

The problem with light can arise from hydroponic systems with insufficiently powerful LEDs. Lettuce needs LEDs that are at least 20 watts. Also the LED panel should have blue and red colors.

Another case is that over time the LEDs burn out due to exhaustion of their resource. As a result, the light becomes weaker and weaker and the plants begin to suffer.


  1. Make sure your lettuce gets enough light.
  2. If you are using LEDs, make sure they are at least 20 watts.
  3. Make sure all LEDs are working and if not, replace them.

Water aeration

One of the advantages of hydroponics is that the water is very well oxygenated. Most systems have pumps that move the water and oxygenate it. This greatly increases the growth rate of the lettuce.

If the hydroponic system does not have a water pump or air stones, the lettuce will grow slower.

Another case is when the pump has failed and this will definitely affect the growth of the plants. This often happens due to clogging of the pump and some other reasons.


  1. Make sure that the pump in the system is working. If not, repair or replace it.
  2. If your system does not have a water pump, upgrade with air stones and an air pump.,
  3. Avoid having the plant submerged in water. Only the roots should be in the water. The place where the stem comes out of the sponge should be above the water level.

Air Сirculation

In nature, plants are constantly blown around by the wind. This ensures good aeration and evaporation of moisture by the leaves. This also greatly reduces the possibility of disease.

To grow lettuce successfully on hydroponics you need to recreate natural conditions. Otherwise it may grow slowly or get sick.


  1. Plant the lettuce in such a way that there is free space for air movement between the bushes.
  2. Install a fan to regularly ventilate the hydroponic system with the lettuce.


In conclusion, if you give your lettuce enough light and plant food, change the water regularly and adjust the pH of the water, it will grow quickly and vigorously.

Of course during growth there may be some stunting due to various stressors, such as sudden changes in temperature, but overall everything will be fine. Also you need to realize that lettuce is a living creature and can have its own rhythm.

This is the end of my story. I hope you have found answers to your questions here. I wish you good luck and all the best!