Category Archives: Grow Medium

Hydroton Expanded Clay Pebbles

hydroton expanded clayWhat Are Hydroton Expanded Clay Pebbles?

Hydroton is a brand name that is interchangeably used with expanded clay and clay pebbles. It’s one of the most popular grow mediums used by hydroponic gardeners. Hydroton expanded clay pebbles come from mined clay that is heated in a kiln to over 2000 degrees. This causes the material to expand like popcorn making it light and porous.  Hydroton expanded clay pebbles are lightweight and can come in circular ball shapes varying in sizes. Hydroton doesn’t compact and since it’s porous, allows for excellent water and airflow.

How Do You Use Hydroton Expanded Clay Pebbles?

Hydroton expanded clay pebbles can be used alone or in with a combination of other grow medium. I prefer to use them as a standalone in my hydroponic systems. Before using any expanded clay, you must completely rinse the dust from the grow medium. Even if your expanded clay pebbles come “prewashed”, I would still recommend rinsing it as a precaution. During transport, pebbles rub together and can sometimes get crushed causing dust. Dust from the expanded clay can cause clogs and also wear on pumps.

Some seeds can be germinated in hydroton expanded clay pebbles under the right conditions. I was shown by a friend that crushing pebbles actually makes them more suitable for seed germination. I prefer to start seeds in rapid rooter cubes and transplant them into the hydroton.

Come harvest time plants are easily removed. After harvest, hydroton expanded clay pebbles can be sterilized and used again. I prefer to use a hydrogen peroxide mix, some prefer to use bleach. The hydroton should be soaked for a few hours and then rinsed. If using bleach I would especially recommend rinsing a few times.

What Hydroponic Systems Work Well When Using Hydroton Expanded Clay Pebbles?

Hydroton can be used in a few different types of systems. It is often used in drip systems, ebb and flow, deep water culture and aeroponic systems. Since these types of systems provide constant nutrient solution to the plants, it ensures the hydroton doesn’t dry out. Hydroton expanded clay pebbles can be used in net pots or large grow beds.

Hydroton expanded clay pebbles in flood and drain system

A few week old lettuce in Hydroton expanded clay grow medium.

Advantages To Using Hydroponic Expanded Clay Pebbles

  • It maintains a neutral pH.
  • Retains some water but doesn’t suffocate roots.
  • You can allow the hydroponic system to continually run, providing more nutrients to your plants.
  • It drains water well.
  • Comes from clay, which is abundant, so it’s environmentally friendly.
  • It’s reusable and can last a long time.
  • Can be inexpensive in small quantities.

Disadvantages To Using Hydroton Expanded Clay Pebbles

  • If the system fails hydroton can dry out.
  • Hydroton needs to be rinsed thoroughly before using.
  • Dust from hydroton can wear on pumps.
  • Can be expensive if using large grow beds.

Using Rockwool For Seed Germination

Rockwool is a popular starter medium that has been used a long time with hydroponics. Smaller rockwool cubes are used for cuttings or seed germination and then transplanted into hydroponic systems. Larger cubes or slabs can be used to grow larger plants. It works well as a grow medium because it’s great at both maintaining moisture and allowing air to the roots. Rockwool is not pH balanced and will need to be adjusted before getting started.

Preparing Rock Wool For Seed Germination

  • The pH of the rockwool will first need to be brought down. This can be used with either a pH lowering product or a lemon. When handling rockwool, it is important not to squeeze it or it may alter the air flow to the roots. Lack of air flow causes root rot.
  • Get a bowl of water and something to measure the pH of the water. The goal is to get the water to a pH measurement around 5.5. To do this you want to add a small amount of your pH lowering agent or lemon juice until you reach the correct measurement.
  • Next, you want to soak the cubes in the treated water. It needs to be soaked for 10 seconds.preparing rockwool

How to Germinate seeds in Rockwool

You need to have an area ready to place your cubes after they are done soaking. I find using a domed tray that acts as a mini greenhouse works well for germination and need less watering. After the rockwool is done soaking, take the cubes out of the water and line them up for seeds or cuttings. Most rockwool comes with holes already made, but if not you will need to make a hole in the top of the cube. You can do this by cutting a 1/4 inch deep slit or hole in the top of the rockwool.

I suggest placing a few of seeds in the rockwool to increase the chances of getting a healthy sprout. If you only plant one seed and it doesn’t germinate you’ve lost some time. If several sprout you then have the option of choosing the healthiest looking seedling. With most vegetables, I use 2 or 3 seeds and with herbs, I use a few more. The seeds should be placed at the bottom of the hole to escape the light. Put the rockwool in an area that will stay between around 70 to 80 degrees.

After a few days, you will hopefully see few sprouts start to pop up out of the rockwool. The cubes lose a little moisture over time so you will need to maintain the moisture needed for the plant to grow. I use a spray bottle a low dosage of nutrients and moisten the rockwool about once a day. After several days, find the heartiest looking seedling(s) to keep and clip the rest. It’s important to clip and not pull or you may disrupt the root system of the other plant you want to keep. When the root system starts to show out of bottom of the cube it is time to transplant into the hydroponic system. Be careful not to place the rockwool below the grow medium your transplanting it in or water will puddle, increasing the chances of root rot.

7 Different Hydroponic Grow Mediums

Hydroponic grow medium

Some commonly used hydroponic grow mediums

Many different types of grow medium can be used in hydroponics.  There really is no right answer to the question of what hydroponic grow medium works the best. It varies depending on what you’re growing, the type of hydroponic system you’re using, and your personal preference. There could be several grow mediums that could fit your needs which may bring it down to price and availability. Here’s an overview of some of the main hydroponic grow mediums used.


Rockwool is a long used hydroponic grow medium, especially when it comes to starting plants or starting clones. It has to be ph balanced before being used. This is done by soaking the cubes ph balanced water. Rockwool is made to have a perfect airflow for plant roots to it’ important to not squeeze the cubes. Rockwool is a porous medium that is made up mainly rock, which is heated, melted, spun into strands, and then formed into cubes, blocks, or slabs. You can find rock wool at online or at your local hydroponics store.

Oasis Cubes

Oasis cubes are a grow medium designed for both seeds and cuttings. It’s similar to rockwool, used for germination, but does not have to be pre soaked. It is a medium that has a neutral ph and great water retention. It’s pretty versatile as it can be transplanted in many different types of hydroponic systems and grow mediums.

Expanded Clay Pebbles

Expanded clay pebbles are often referred to as hydroton, which is actually a brand name, or just clay pebbles.  It provides a great support for the plant, fits well into net pots and has a neutral ph. This is not the cheapest hydroponic grow medium to start out, but can be cost-effective if growing is a long-term hobby or investment. After harvesting your garden, expanded clay can be cleaned and reused for your next crops grow medium. Its many benefits and ease of use mean it’s available in almost every hydroponic shop. Make sure to not breathe in dust and rinse well before using.

Coco Fiber/chips

Coco chips and fiber come from the husk of coconuts. This is an organic grow medium that is quickly picking up in popularity among hydroponic growers. It provides great moisture retention while also allowing great air flow to the roots. This hydroponic grow medium comes in 2 forms, chips and fiber. The chip form is similar to wood chips while the fiber is stringy.


You may be familiar with perlite as an additive to garden soil. This hydroponic grow medium allows oxygen to get to the roots and better water drainage. It is a type of volcanic glass that, when heated, pop similar to popcorn. Perlite can be used alone in hydroponic systems like the drip system, but it doesn’t retain water very well. It also floats, so it doesn’t work well as a standalone in some hydroponic systems. It is often mixed with other grow medium such as vermiculite; a 50/50 mix works well. Perlite is inexpensive and is also reusable. The dust from perlite is not healthy for you or your plants, so make sure to wear a mask and rinse it before use.


Vermiculite is a mined mineral rock. There a different types of vermiculite, so make sure you’re getting some that works with hydroponics. Vermiculate as a hydroponic grow medium is very good at retaining moisture, but when used alone it can be too much moisture for healthy roots. Its most often used in conjunction with another grow medium like perlite. This gives the roots the moisture it needs while the perlite allows sufficient oxygen to the roots.


I’ve had a lot of success using different types of rock and gravel from the hardware store as my hydroponic grow medium. It’s easy to come by and when a lot of grow medium is needed, such as in a flood and drain system, rock is one of the more cost-effective grow mediums to choose from. I’ve found pea gravel, lava rock and river rock to work well with many of my hydroponic systems as grow medium. Another thing to keep in mind is heat. The sun will heat rock which will in turn raise the temperature of your hydroponic nutrient solution.

There are many things that could be used as hydroponic grow medium. Really anything that a plant can grow in would be considered a medium, including air (Aeroponics). Hydroponic grow mediums have to allow both oxygen and water to the roots while securing the plant into your hydroponic system. Unfortunately there is no real answer to what hydroponic grow medium works best. It takes experimentation with different types to find what works best for you!