Image above: Hydroponically grown tomatoes
Hydroponics is a way to grow plants without soil. If you have grown a cutting in water, you have dabbled in a form of hydroponics. However, it’s more than just placing a plant cutting or a whole plant in water (this is known as ‘hydro’ by most indoor plant enthusiasts). Some hydroponic systems have roots constantly submerged in running oxygenated water, while other systems use inert media like clay balls or lightweight expanded clay aggregate (LECA), recycled glass, vermiculite, perlite or coconut coir in place of soil. Nutrients are carefully measured and added directly to the media or oxygenated water – in a controlled manner – to help optimise plant growth.
One of the key advantages of growing in a soil-less medium is the absence of soil-borne pest or disease issues – no annoying fungal gnats, no issues with crown-rot, root-rot or collar-rot, and no on-going additions of soil conditioners. It also removes the need to mulch as there is no need to help the media retain moisture or suppress weeds.
Hydroponics has been used successfully in commercial horticulture since the 1970s, but there are hydroponic kits that are now available, making it easy for everyone to grow hydroponic plants at home. You can also DIY systems to accommodate your growing houseplant collection.
As hydroponic systems are mostly used indoors, in glasshouses, or in dedicated grow rooms, they do not necessarily have access to sunlight. It is very likely you will need to provide an artificial light source or a ‘grow light’ (see Grow light) to assist with plant growth.
With every growing technique, there are of course disadvantages too. Depending on the system you choose, the initial outlay may be more expensive than growing in a traditional pot and potting mix, especially as there are a few specialised tools required to help start and maintain the system. It may be best to start off with an all-in-one hydroponic kit and once you’re comfortable, start experimenting with the other methods. These kits are usually small enough for your kitchen bench or side table, and allow you to grow a mix of pocket-sized herbs or greens.
While most plants can grow in hydroponics, the media is not cohesive and therefore, it can be difficult to support large or top-heavy plants. You can grow a peace lily, but it’s unlikely you will be converting a large, well-established fiddle leaf fig, unless of course you can provide it with substantial support.
Image above: Syngonium spp. growing in a glass bottle of water
Let’s explore a few of the options on how to grow hydroponics plants at home.
You may have heard of the terms “hydro” or “converting plants to hydro”. They typically refer to completely removing the potting mix from the plant’s roots and placing it into a vessel filled with water. It’s a decorative way to display plants and it’s easy to do as it requires hardly any setup, aside from an ornamental bowl or glass jars. This form of hydroponics is better suited to indoor plants, as opposed to herbs and vegies.
How to Prepare Plants for Hydro
To convert your plants to hydro, remove the plant from its pot and tickle the root ball to loosen the mix from the roots. Once the bulk of the mix is removed, place the roots under running water to help rinse off any remaining mix. Also, take the time now to prune away any dead or kinked roots. Once clean, part fill a glass jar or bowl with water, float the plant in the centre and backfill with more water, if needed.
Unfortunately, growing plants in hydro is not a long-term solution. New leaves, shoots, and roots will grow, getting by with the minerals in the water and any stored nutrients in their tissues. However, they will not grow to their full potential. After some time, you may notice that new growth is smaller and older leaves may yellow and drop as soon as new ones appear.
While you can add nutrients to the water, many manufacturers do not list instructions on how to dilute products specifically for hydro plants. For a gentle approach, you can try diluting liquid fertilisers to quarter-to-half strength and adding to the water once a month during the warmer months or periods of active growth. Alternatively, you may like to try foliar feeding.
Image above: growing herbs in a home hydroponics kit
There are various hydroponic systems available, including:
All these systems – aside from hydroculture – require access to electricity to pump air and/or water and nutrient-solution to the plant roots.
Image above: Hydroponics system growing leafy greens
Passive hydro is one of the easiest hydroponic systems to set up at home. Flood and drain, and DWC systems are also possible but require more space to set up. Whatever system you choose, there are a few key items you will need.
What You Will Need
Most of the growing media available for hydroponic systems have very similar qualities. They’re porous, so they’re able to hold moisture and release it for use as plants need it. They all use a process known as capillary action to draw or ‘wick’ the nutrient solution from below and the spacing between the particles help provide valuable oxygen to the plant’s roots.
Clay balls or LECA: This is one of the most common media forms used for hydroponics. Clay balls are sold under various trade names, but essentially are pieces of clay that have been fired and shaped into balls. It has a neutral pH and can be reused indefinitely. Due to the size and shape of the balls, there is a good amount of spacing between each ball and this helps provides oxygen for the plant roots. Available in varying sizes, but 50-100 mm is suitable for most houseplants.
Perlite: Has very similar qualities to LECA, but smaller in size. As such, it’s denser and can hold more water. However, if a plant’s root system is aggressive, it can fill up the spaces between the perlite and cause issues with drainage.
Foamed glass: This medium is made entirely out of recycled glass. The glass is diverted from landfill, broken down into fine particles and processed into irregular-shaped aggregates. It has very similar qualities to LECA but may be a little more expensive due to the processing required to achieve the final product.
Whether you choose hydroculture, flood and drain or a DWC system, the plant(s) need to be prepared for conversion. See How to prepare plants for hydro to remove the potting mix from the plant’s roots.
There are a couple of ways you can convert plants to hydroculture. Two of the easiest methods include: single sealed pot and pot in pot or pot in saucer.
This involves the use of one clear pot with no drainage holes. It can be plastic or glass, but it needs to be clear so that you can see when the nutrient solution needs to be replenished. To convert plants to this method, part-fill the pot with your chosen media, position the plant in the centre and backfill. Fill one-third of the pot with the nutrient-solution and position in desired spot. Top up the solution as needed.
All hydroponic systems should be flushed regularly to reduce salt build up and prevent nutrient imbalances, however, as there are no drainage holes, it is difficult to regularly clean this system. The pot will need to be filled with water and carefully turned upside down to allow the water to completely drain.
Pot-In-Pot or Pot-In-Saucer
This involves planting into a pot with bottom drainage holes and sitting the pot inside a larger sealed pot, tray or saucer. The pot, tray or saucer acts as an external reservoir and water and nutrients are drawn via capillary action as the plant needs. Ideally, the external pot or saucer should be clear so it’s easy to see and top up the solution as needed. The reservoir should be at least one-third the height of the internal pot. Use a tray if you have several plants growing in hydroculture.
This method also allows the media to be easily flushed as the water will simply drain away.
Preparing the nutrient solution can be a little tedious, but once you have got the method down pat, it’s easy to repeat. Use these steps as a guide and adjust to suit your plant needs.
What You Will Need
Step 1. Fill one jug with 1 L of water. You can make up more depending on how many plants you have. Check the pH and use the pH adjusters to bring the pH to 7.0. Follow the instructions on the back of the pack – you do not need a lot of the solution to adjust the pH, so it’s best to add or pipette a little at a time. Take note of how many drops were needed to avoid having to measure the pH each time.
Step 2. Fill the remaining jug with 1 L of water. Shake the hydroponic fertiliser concentrate and add a few millilitres of the concentrate to the water. Agitate the water to mix well and check the EC. The optimal EC is between 0.7-1.0, so continue to carefully add until this is reached. Take note of how many drops were needed to avoid having to measure the concentrate each time.
Step 3. Check the pH of the nutrient solution. This is done after the nutrients have been added as they can affect the pH. Adjust as needed to get the pH between 5.5-6.5. Again, take note of what was needed to avoid having to measure again in the future. However, it’s good practice to measure every now and again to ensure your recorded measurements are still within range.
Step 4. Fill one-third of the sealed pot or pot in pot/saucer with the nutrient solution. While it will be taken up by the plant, it will also be subject to evaporation. As the level decreases, top it up with the pH neutral water. Continue to top up with pH balanced water for the next two weeks.
After this time, you can top up with a mix of the prepared nutrient solution and pH neutral water, but only continue this for the next 1.5-2 weeks. You may find you can top up the solution for longer or shorter periods, but it will come down to trial and error to know what works best with your plants.
At the end of 3.5-4 weeks, the system will need to be flushed. Remove pots from the saucer or tray and place under running water for one-minute or so, to help remove any crusted salts on the growing media. You can also clean the saucer or tray at this time, if needed. Replace the pots on the saucer or tray and add the nutrient solution to repeat the process.
Image above: Commercial hydroponics set up using LED grow lights
If your hydroponic system does not have access to sunlight, you can use grow lights as an alternative light source. The easiest way to purchase a grow light is to look for ones specifically marked as a ‘grow light’. Most of them are available as LED lights, so they’re energy efficient and won’t heat up.
While it’s tempting to leave your grow light on 24/7 – don’t. There is such a thing as too much of a good thing. Plants need rest, too. Most plants will grow well with 12-16 hours of light, with flowering plants at the top of that range. Ensure your plants have at least eight hours of darkness.
Growing plants in hydroponics has a range of benefits, but it is a little tedious to set up and it can take some time to adjust to a new style of gardening. However, like any new hobby, it will take a bit of trial and error to get it right, but once it’s established, its smooth sailing.