General Hydroponics

General Hydroponics: Find out why you should build your own hydroponics system while learning everything you need to know about hydroponic setups.

What is Hydroponics?

Hydroponics is a method of growing plants without the use of soil. With the method I use, and detail on this page, plants are grown in an absorbent aggregate with hydroponics nutrients. Some of the advantages of house plants grown in hydroculture are:

  • The water reservoir makes it easy to see when the plant requires water
  • The aggregate is open..therefore allowing air to circulate around the roots
  • The reservoir, coupled with using absorbent aggregate, helps create humidity around the plant. This method of hydroculture is sometimes referred to as 'passive hydroponics'.

There is another method, which uses nutrient solution, called 'active hydroponics' or often referred to just as hydroponics. This system often uses a form of nutrient delivery system that delivers the nutrients to the roots. I will only be detailing the method of house plant hydroculture on this page.

The word "hydro" derives its name from the Greek word "hudor" meaning water, hence hydroculture = water culture.

General Hydroponics Aggregates

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I use expanded clay pebbles which are specifically sold for general hydroponics. I get my expanded clay pebbles from a hydroponics stockist who stocks them in 2 gallon and 10 gallon bags. These are made of clay, which has been fired to a high temperature to create a hard outer shell and a honeycomb-like center that allows for water absorption. I clean these as described in the cleaning section of this page.

Aggregate performs a similar role to that of soil, in that it supports the plants. Expanded clay pebbles have the ability to absorb nutrient solution. They then transfer it through the aggregate via a capillary action..from a reservoir, then to the plant roots.

A search on the internet for hydroculture, passive hydroponics or general hydroponics usually leads to various supplier sites who stock suitable aggregates. Some offer it in various sizes and I usually use the smaller pebbles for fine rooted plants and the larger sizes for all others.

Hydroponic Nutrient Solution

This is the 'food and water' for the plants. Special hydroponics nutrients are available for general hydroponics. These usually come in either powder or liquid form (which are added to water to make a solution), or in a resin or tablet form (which is added to the aggregate or reservoir.) With the resin form, the food is slowly released over long periods of time, often months.

General hydroponics nutrients differ from some house plant foods in that they contain extra trace elements. Some nutrient solutions may not be suitable for indoor house plant hydroculture. I always check the suitability with the manufacturer first. Instructions on the use of nutrients should be supplied with them.


Nutrients are available in many different NPK (N=Nitrogen, P=Phosphorus, K=Potassium) formulations. These are expressed as percentages. By selecting different NPK formulations, the growth, flowering, or crop of the plant can be controlled to a certain degree. I use a general purpose nutrient for all my plants but some plants may appreciate a different formulation.

Have any questions? Ask them here.

Converting Plants For General Hydroponics

The easiest method I have found for converting a house plant to general hydroponics, is to use one that has been water rooted . The root system seems to be slightly different to one that has been grown in soil . The method I use is to take a soft stemmed cutting and suspend it in a container full of water. This can be done by placing a piece of cardboard on the top of the container and putting the cutting through a hole in the center.

The cutting is then put someplace where it will get light (but not direct sunlight), and also somewhere that is not too hot. The water in the container is changed every few days to stop it from becoming stagnant. When a good root system has developed, the cardboard is carefully removed....avoiding damaging the plant. The plant is then transferred to general hydroponics as described in the containers section. Then I place the plant into a propagator. You can also place a transparent plastic bag with air holes over it to keep the humidity high for up to 1 month and I also use only water, not nutrient solution, for this time.

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Converting Plant To Hydroponics

Although water rooting is possibly the most reliable method of getting a house plant into hydroculture, it is not my preferred method. I'm a little impatient, and I like to see quick results. Therefore, I prefer to convert a soil (compost) rooted house plant. I always use young houseplants, since large or established ones may be more difficult to convert to general hydroponics. The method I use is detailed below:

  • I soak the plant in its pot, in room temperature tap water up to the height of the top of the soil for approximately one hour. This helps soften the soil from around the roots.
  • Remove the plant from the pot, place the plant roots back into a bucket of clean-room-temperature water, and agitate to remove most of the soil.
  • Remove the plant from the bucket then run room temperature/clean water over the roots until all the soil is removed. It is important to remove ALL the soil.
  • Cut off any dead roots. Trimming the roots a small amount seems to help the plant establish better.
  • The plant is placed into a hydroculture pot as described in the containers section.
  • Water only is added, no nutrients.
  • I don't add nutrient solution for approximately 4 weeks, only water. The plant will be very sensitive until it has grown a new root system so it will need nurturing for a few weeks, to do this I place the plant into a propagator or place a transparent plastic bag, with air holes, over it to keep the humidity high.

Hydroponic Containers

I currently use the pot and saucer method. This uses pots made of an inert material such as plastic.

Plants need converting before they are used in hydroculture.

Pot and Saucer:

This method uses a standard plant pot, with bottom drainage holes, which is then placed into a large flower pot saucer. A saucer which is larger than the usual size for the pot is chosen so that it can work as a reservoir. I try to select one that will hold enough nutrient solution for approximately 1 week. The nutrient solution is stored in the saucer. It is possible to get transparent saucers. These make checking the nutrient solution level even easier!!

If several plants are grown in close proximity, instead of using a separate saucer for each plant, a large watertight tray can be used to house several containers. A tray without drainage holes, such as a garden tray or a gravel tray, is used. It's then filled with enough nutrient solution to last for approximately 1 week.

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Converting Plant To Hydroponics

Pot in Pot Method:

This is very similar to the pot and saucer method above, except that the plant pot is placed into a watertight container instead of a saucer. A plastic container, which is slightly larger internally than the plant pot by approximately 1/2 inch all around, is chosen. This allows space which will act as the reservoir. With this method, it is more difficult to see the nutrient level. So the pot either needs taking out or a level indicator needs to be used in order to check the nutrient level.

Alternatively, a transparent plastic container can be used. With this method, I try to get a nutrient level height of approximately 1/4 of the inner pot. The level is measured when the system is assembled. In other words, when the fully planted pot is placed inside the container.

Level Indicator:

It's possible to do a homemade level indicator. I've tried several methods over the years and one of the most successful methods utilizes a plastic tube. Such as a 3/4 inch rigid plastic water pipe or rigid plastic conduit, and a plastic drinking straw. The plastic tube goes in the inner pot and sits on the bottom. There's a small notch in the bottom of the tube to ensure that water can enter and exit it. Make sure that the notch isn't large enough to allow aggregate to enter the tube. The straw has the bottom end sealed, cause if it's not sealed, then it will not float.

Two marks are drawn on the straw to indicate minimum and maximum nutrient level. To set the marks, I assemble the inner and outer pot without any aggregate, and then put the plastic tube in place. Next, put the straw into the tube and draw a line around it level with the top of the tube-this is the minimum level. Now I put water in, approximately 1/4 of the height of the pots, and draw another mark around the straw-this is the maximum level.

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Converting Plant To Hydroponics

Commercial Kits For General Hydroponics:

Want an easier method...a shortcut maybe? There are commercial hydroponic kits available which use an outer watertight pot and an inner pot which have drainage holes or slots. These kits usually come with a nutrient level indicator which makes it very easy to see exactly when they need topping off. The manufacturers/suppliers of these kits can usually supply nutrients as well.

Have any questions? Ask them here.

Potting For General Hydroponics

House plants need converting prior to being used in general hydroponics; Refer to the converting plants section on this page.

Potting is done in a similar way to potting in soil, except that aggregate is used. Aggregate is place in the bottom of the pot to approximately 1/3 the height of the pot. The plant roots are held, suspended in the pot, then aggregate is poured around the roots to the same height as the plant was originally potted. I tap the pot to ensure that the aggregate fully surrounds the roots. Then, room temperature-tap water is ran through it.

When a plant is first transferred to hydroculture, the roots sit in the clay pebbles and not the water/nutrient solution. The plants' roots will receive moisture from the reservoir through the capillary action of the aggregate. This is why the base of the pot is filled with clay pebbles and the roots are placed on top of them.

It is also necessary to ensure that the reservoir is not too deep as this will also cause the roots to sit in the water/nutrient solution. When the plant is established, it may grow roots downwards into the reservoir. This seems to be OK with the plants I have grown.

Nutrient Level

A nutrient solution is made by following the manufacturers instructions, and this is then added to the pot and allowed to drain through into the reservoir. Be careful to not overfill the reservoir. I allow the level to fall until no nutrient solution is in contact with the bottom of the pot before adding more. Some plant pots have feet on the bottom of them which stand the base of the pot off of the reservoir by a small amount. With these, I don't let the reservoir empty. I top it off when the nutrient level falls to the top of the feet.

When the reservoir has emptied, the aggregate can dry out quickly, especially on hot days. Some plants are not tolerant of dry aggregate so I add nutrient solution as soon as the reservoir empties.

As mentioned above, there are slow release resin nutrients available. These are usually added to the aggregate or reservoir, depending on the manufacturers instructions, and will release nutrients slowly for several months. If these are used, it is only necessary to add water to the plants. The resin will need re-adding when they are exhausted.

Tap water is used for making the nutrient solution. I allow this to stand for several hours to reach room temperature.

Hydroponic Plants

I tend to experiment with commonly available plants and see if they will convert to hydroculture. The majority of the plants I have tried, convert successfully but...I have had a few failures. It's impossible for me to say if the failures are due to the plant not liking hydroculture or whether it's because I tend to experiment with techniques and may get it wrong sometimes.

Light For General Hydroponics

Nothing special here. Hydroculture plants seem to have the same light requirements as soil grown plants. I follow the recommendations on the plant label or use a house plant reference book. For more on indoor lighting, click here.

Cleaning For General Hydroponics

Cleanliness of the equipment helps to reduce the risk of plant disease. The hydroculture equipment I use is cleaned, before it is used, using the following methods:

Cleaning Aggregate:

  • Thoroughly rinse with clean water until the water is clear.
  • Place aggregate into a bucket.
  • Fill the bucket with tap water.
  • Leave to soak for approximately 1 hour.

Cleaning Pots:

  • Place pots into a bucket containing clean water and a small amount of dishwashing liquid.
  • Using a small soft clean brush, scrub the inside and outside of the pots.
  • Thoroughly rinse the pots with clean water.

After Care For General Hydroponics

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Converting Plant To Hydroponics

Apart from ensuring that the plant receives nutrient solution when required, there is very little aftercare involved.

The plants appreciate being washed from time to time. This helps to remove any dust which has settled on the leaves and salt or nutrient build-up in the aggregate. I also wash out the saucer/pot container at the same time. Both are done once a month. The pot is removed from the reservoir and placed under a room-temperature-running shower or slow running tap. After cleaning is finished, excess water is allowed to drain. The pot is then placed back into the reservoir, and nutrient solution is added.

Plants need re-potting into larger pots as they mature. I do this when the roots start to grow through the drainage holes in the pot. Care is taken when removing the plant from the pot to avoid ripping or breaking too many roots.

Extended Watering For General Hydroponics

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If it's necessary to extend the watering period, then I use a larger reservoir...such as a garden or gravel tray that doesn't have drainage holes. The pot is removed from the reservoir and then placed in the tray. Next, the tray is filled with water up to the height that nutrient solution is usually added.

It's best not to do this too often, as the larger reservoir means that the aggregate will stay wet for longer. Some plants like to dry out slightly between watering.


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