Hydroponic Water Temperature: What Is The Ideal Water Temp For Hydroponics

By: Teo Spengler

Hydroponics is the practice of growing plants in a medium other than soil. The only difference between soil culture and hydroponics is the manner in which nutrients are supplied to the plant roots. Water is an essential element of hydroponics and the water used must stay within the appropriate temperature range. Read on for information about water temperature and its effects on hydroponics.

Ideal Water Temp for Hydroponics

Water is one of the mediums used in hydroponics but it is not the only medium. Some systems of soilless culture, called aggregate culture, rely on gravel or sand as the primary medium. Other systems of soilless culture, termed aeroponics, suspend the plant roots in air. These systems are the most high-tech hydroponics systems.

In all of these systems, however, a nutrient solution is used to feed the plants and water is an essential part of it. In aggregate culture, the sand or gravel is saturated with the water-based nutrient solution. In aeroponics, the nutrient solution is sprayed on the roots every few minutes.

Essential nutrients that are mixed into the nutrient solution include:

  • Nitrogen
  • Potassium
  • Phosphorus
  • Calcium
  • Magnesium
  • Sulfur

The solution may also include:

  • Iron
  • Manganese
  • Boron
  • Zinc
  • Copper

In all systems, hydroponic water temperature is critical. The ideal water temperature for hydroponics is between 65 and 80 degrees Fahrenheit (18 to 26 C.).

Hydroponic Water Temperature

Researchers have found the nutrient solution to be most effective if it is kept between 65 and 80 degrees Fahrenheit. Experts agree that the ideal water temperature for hydroponics is the same as the nutrient solution temperature. If the water added to the nutrient solution is the same temperature as the nutrient solution itself, the plant roots will not suffer any sudden temperature shifts.

Hydroponic water temperature and nutrient solution temperature can be regulated by aquarium heaters in winter. It may be necessary to find an aquarium chiller if summer temperatures soar.

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Read more about Container Gardens

How to Keep Water Cool in Hydroponics: 8 Easy Ways

One thing growers should never overlook in their hydroponic system is the temperature of their nutrient mixture. As soon as the temperature reaches over a certain point, the solution can’t hold the dissolved oxygen as long.

Add to this, when there are unhealthy root masses mixed with these temperatures, it creates the perfect place for pathogens like root rot to take a foothold. To combat these problems, you need to make sure your nutrient solution remains between 65 and 75 degrees.

Here we will look at ways to cool your hydroponic reservoir and solution. While these can make the difference, some of these methods come with their own downsides when in use.

In summary, according to other sites such as NoSoilSolutions and Epic Gardening, here are the main eight ways to cool a nutrient reservoir.

  1. Keeping your reservoir in the shade
  2. Paint your reservoir to reflect light
  3. Increasing the size of your reservoir
  4. Top off your nutrient solution
  5. Bury your reservoir in the ground
  6. Making a swamp cooler
  7. Making your own cooling coil
  8. Purchase a water chiller

How Can I Cool My Hydroponic Reservoir?

Here we will take an in-depth look at the above methods. The first couple of entries in the list should ideally be done as a matter of course. Aside from controlling temperatures, they help prevent light entering and the growth of algae.

Build Your Hydroponic System in the Sun

An extremely gorgeous head of red cabbage grown outdoors hydroponically. Source: square foot hydroponics.

One of the primary benefits to growing outdoors hydroponically is the free lighting you get from the sun. Summer sunlight is much better than any grow lamp or artificial light source. In fact, the sun is basically the “outdoor hydroponic grow light” of the universe, so make sure you take advantage of it!

If possible, choose a spot with southern exposure that’s properly sheltered to build your hydroponic system. You can use a tool like Suncalc to determine how the sun travels over your property. By doing this, you’ll be amazed at the speed at which your plants grow when given all of the sun they need.

What is the ideal hydroponic reservoir temperature?

The temperature of water and its oxygen content are closely related, and the temperature of the solution needs to be fairly closely monitored in order to maintain dissolved oxygen levels. At low water temperatures, the plants go into shock, but as the temperature rises in the tank the solution loses the percentage ratio of its oxygen content. Here are some figures:

Tank temperature & % of oxygen in the solution (ppm)

10ºc (50ºf) 13 ppm 20ºc (68ºf) 9-10 ppm 30º (86ºf) 7 ppm As you can see the oxygen content in the resolution approximately halves for every 10ºc rise in solution temperatures. ok got that! :)

In easy terms, ideal temps are between 18 and 20 ºc and if your water temps are anywhere near 25 -30ºc then the oxygen levels can be as much as half of the desired levels. In easy terms, ideal temps are between 18 and 20 ºc and if your water temps are anywhere near 25 -30ºc then the oxygen levels can be as much as half of the desired levels.

BUT As a direct result of the water temperature being at higher temps the plants will need more oxygen at the roots so the problem is almost squared and there is 25-40 % less oxygen in the solution and the plants will need double the amount than normal. In real terms the effect is that the oxygen level in the solution is only at 25 % of the desired levels and you can chuck as much light or feeds at them as you like but if they are only running at 25% of the required dissolved oxygen levels then this is hardly conducive to happy healthy growth is it?

Some of the results of low oxygen levels in the rez tank are:

  1. roots are unable to work effectively, leading to:
  2. a build up of toxins meaning that the plant will be unable to take up the water and feeds needed for healthy growth
  3. The whole plant begins to deteriorate as photosynthesis and carbohydrate rates slow leading to wilting.
  4. Leaf damage and root die-back. Ethylene is released and causes a toxic overdose and the roots fail.
And all of the above cause ideal conditions (especially in warm water) for every hydroponic growers worst enemy:

So of course the real solution to high water temperatures in a hydroponic reservoir is a water chiller. We tried inserting bottles of ice water into the res tank but despite dedicating a small chest freezer to the production of ice, found it almost impossible to sufficiently and consistently cool our water (warmed by hot sunshine on the pipes outside). Its yet another expensive piece of kit to add to the grow room, but if you are growing hydroponically in an environment where water temperature rises either due to external environment (like ours) or internal environment (the tank is warmed by heat thrown out by your HPS), then a water chiller IS be the only solution. This great chiller features:

  • digital display
  • titanium heat exchanger
  • super quiet operation
  • powerful compressor

And of course if the problem is that your water temps are too low, then its worth investing in a water heater to maintain a healthy temperature:

Different Plants, Different Needs

An electronic timer is especially necessary if you are growing a variety of different plants. Although you can follow the general guidelines above and have success, some plants do much better with longer or shorter periods of “daylight.” If you have a mix of these in your garden, you will need to figure out a custom schedule. An electric timer allows you to take care of this hassle-free and change it according to your needs as your garden evolves.

Short day plants: These require a long period of darkness to photosynthesize and produce flowers. If they are exposed to over 12 hours of light per day, they will not flower. Poinsettias, strawberries, cauliflower, and chrysanthemums are short-day plants. The short-day cycle mimics the environment in nature for plants the flower in the spring.

Long day plants: These require up to 18 hours of sunlight per day. They include wheat, lettuce, potatoes, spinach, and turnips. The long-day cycle mimics the natural environment of summer-flowering plants.

Day-neutral plants: These are the most flexible. They produce fruit no matter how much light they are exposed to. Some examples include rice, eggplant, roses, and corn.

If you must mix sort and long day plants, it is best to compromise their needs and pick a lighting schedule that is right in the middle, around fourteen hours of light per day.

Types of Hydroponics

Though hydroponics often means growing plants in water, other types of hydroponics offer similar benefits. Some plants have marbles or gravel holding their roots in place, while others have hanging roots that require regular misting instead of traditional watering. With a continuous flow system, plant roots enjoy a constant flow of nutrient solution, typically from pipes. And when growing plants in water, gardeners typically add nutrients to the water to feed the plants.

Option 2: The Kratky method

  • Mason jar
  • Rockwool cubes
  • Seedlings
  • Net cups (size should be the same in diameter as the lid of the Mason jar)
  • Clay pebbles
  • Paper

  1. Drop each net cup into the top of the Mason jar. The lip top of the cup should be resting comfortably on the top of each jar.
  2. Mix your water and grow solution in a separate container and pour enough into each jar that it reaches the just bottom of the net cup. Because this system does not have a pump or air stone, you are filling less of the container so that your plant roots have some exposure to air.
  3. Place each Rockwool cube with your seedling. As previously discussed, ensure the Rockwool is soaked in water before your seeds are planted. The best time for a seedling to be transplanted is at about two inches tall with its true leaves intact.
  4. If your Rockwool cube doesn’t fill up your net cup, use your clay pebbles to take up extra space around the cube. They will also be helpful in blocking out light that comes in from the top of the net cups. If there is light that hits the water, it can result in algae growth inside your container.
  5. Cover all your jars with paper so that there is no glass exposed. You can tape the paper against the jar to ensure it stays in place. This will also prevent algae growth.
  6. Monitor your plants. Ensure your plants are in a well lit space so they can get plenty of sun (10-11 hours) to grow big and strong. And shouldn’t have to change your water nutrients until you’re ready to harvest.

Depending on the plants that you are growing, the ideal pH level in the water will be different. The appropriate pH level depends on the type of plant you’re planning to grow. If you notice your plants aren’t thriving, then that level is likely off, You can check your pH using a test kit that is available to order online, in hardware or home garden stores.

Watch the video: How to drop dwc temps

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