Semi hydroponics, or semi-hydro, is a system of growing plants in an inorganic media rather than soil. Rather, an inert, porous medium draws nutrients and water from a nutrient reservoir to the roots of the plant by means of capillary action.

While there are many different types of set-ups you can use, I like the inner/outer pot method. In this setup, the plant is grown in LECA (or other inert media), in a plastic pot with drainage holes at the bottom. This inner pot then sits in an outer cache pot, or deep saucer, with no drainage holes that holds the nutrient reservoir (hydroponic nutrients diluted in water). When filled, the nutrient reservoir is kept at a 1/3 the height of the inner pot, with the plants roots planted just above the waterline.

A semi hydroponic setup consists of a few basic components. Here’s what you’ll need to get started:

• A plastic inner pot with drainage holes (to house your plant)
• An outer pot or deep saucer with no drainage holes (to hold the nutrient reservoir)
• Your growing media (I like to use LECA)
• Hydroponic Nutrients (I use General Hydroponics Flora Series)
• A pH meter or pH testing kit
• pH up
• pH down

I like to use standard plastic nursery pots with drainage holes at the bottom in various sizes to fit inside of my cache pots, or saucers.

To give you a better idea, the links below show the type of pots I use. Realistically though, any pot with drainage holes at the bottom, placed in reservoir will do.

Amazon US

Amazon Canada

Unless you’re growing orchids, you may want to avoid using net pots. With net pots, as your plant grows, its roots will grow through the slits along the side of the pot, causing them to dry out or air prune with exposure to the atmosphere. This exposure to the atmosphere also causes the LECA to dry out faster and hinders its wicking ability. Additionally, roots growing through the slits makes it difficult, if not impossible, to remove the plant without damaging the roots.

For these reasons I prefer to use standard plastic pots with drainage holes at the bottom. With these pots, the media and roots are shielded from the outer atmosphere, allowing the LECA to remain saturated and maintain its wicking ability, leading to healthier roots in my experience!

LECA (Lightweight Expanded Clay Aggregate), also sold as expanded clay pebbles or Hydroton, is used mainly for growing plants in semi-hydroponics / hydroculture. Since it is a strong and durable clay aggregate, it is used to hold and provide support to the plant and its roots in place of soil. While its porous and wicking structure allows it to absorb, retain and supply water and nutrients to the roots.

LECA is a lightweight, durable clay aggregate formed by heating clay to very high temperatures in a rotary kiln. As the yielding gases expand the clay, they form thousands of air pockets or ‘pores’ – very much like a honey comb. The resulting granules can vary in size and consist of a hard outer shell with a porous inner structure, making them very strong with low density.

I use Mother Earth Hydroton that I buy locally from Urban Gardens LTD., in Dartmouth, NS for around CAD $35 for a 50 litre bag. If you can’t find it locally, check out the amazon links below! Just keep in mind that the prices on amazon tend to fluctuate.

Amazon US

Amazon Canada

You’ll notice that some of the LECA will float when you first add water to the soaking bucket since they contain thousands of small air pockets or “pores”. Soaking the LECA for longer allows them to become more fully saturated by allowing water to pass through the walls and cracks of the outer surface pores into the inner and micro pores. Simply rinsing the LECA on the otherhand, will only saturate the surface pores.

Since LECA works through capillary action, it acts like a sponge, with each piece of LECA absorbing liquid from those nearest with a higher water saturation. Therefore, when LECA is only partially saturated, those nearest the nutrient reservoir must become saturated first, before the ones above begin to pull nutrient solution up until all the LECA is saturated moving to the surface. For this reason, if LECA is not sufficiently pre-soaked, it loses its wicking ability and the continuous absorption depletes the reservoir much faster.

When efficiently pre-soaked, all the LECA from top to bottom should be evenly saturated, stabilizing the wicking process, and the only loss of nutrient solution should be that which is used by the plant or evaporates at the surface. In theory – however – when evaporation is taken into consideration, the LECA nearest the surface will always be much more dry compared to those nearest the reservoir, due to its contact with the atmosphere.

Currently I am using General Hydroponic Flora Series, equal parts each of Flora Micro, Flora Grow and Flora Bloom. Initially, I started by using the lowest recommended concentration on the label, that being 1.25 ml (1/4 tsp) of each per 4 litres (~1 gallon) of distilled water. After a few weeks, I doubled the concentration to 2.5ml (1/2 tsp) of each per 4 litres of distilled water.

These nutrients are available on amazon. See the links below!

Amazon US

Amazon Canada

It is very important to use nutrient solution in a semi hydroponic system since LECA (or any inert media being used), is inorganic and does not contain any nutrients on its own. By using nutrient solution, you are providing the plant with all of the nutrients required for growth, health and vitality. If you were to only use water, the plant will begin to starve from nutrient deficiences and may eventually die.

It is important to use nutrients that are specifically designed for hydroponic systems and not fertilizers used for soil grown plants for a few reasons. The nutrients used for plants in hydroponic systems must be water soluble in order for the plants to absorb them, which is often not the case with fertilizers designed for plants in soil. Furthermore, fertilizers used for plants in soil do not provide complete nutrients for hydroponic growing, since they are designed for soil grown plants that get additional nutrients from the soil itself.

When the nutrient reservoir is full, the oxygen contained in the air pockets of the LECA beneath the waterline dissolves. The dissolved oxygen mixes with water helping roots that have grown beneath the waterline to absorb nutrients.

Therefore, when the reservoir depletes a little, it actually allows the air pockets to refill with oxygen before you top up the reservoir again. However, you should avoid allowing the waterline to deplete too much lower than a 1/3, since this can cause the LECA to become very dry and lose its wicking ability.

I therefore try to top up regularly to maintain the water level at a 1/3 the height of the inner pot, but I don’t panic if the water level depletes ‘somewhat’. Topping up regularly helps to keep the LECA more uniformly saturated throughout the pot and prevents the roots from drying out.

If the root growth becomes so substantial that it has grown down through the reservoir and out of the drainage holes, I either trim the roots back and replant in the same pot, or move to a slightly larger pot.

PH is a measurement on the pH scale that indicates how acidic or basic/alkaline a substance is; that ranges from 0 to 14, with 7 being neutral. As the pH goes lower than 7, the solution is more acidic and as the pH goes higher than 7, the solution is more alkaline.

The ideal pH range for houseplants is slightly acidic and should fall between 5.5 and 6.5. If the pH of your nutrient solution is too high (alkaline), or too low (acidic), you can use pH down or pH up to adjust the pH accordingly. 

I like to use a digital pH meter to test pH, although you can use pH testing strips or a pH testing kit. I prefer a meter over a testing kit because it gives a more accurate and precise reading. Furthermore when using a testing kit, since hydroponic nutrients are coloured, they can affect the colour a testing solution produces, leading to an inaccurate pH reading.

Additionally, I prefer the pH meters with an adjustment screw, as you are not locked into using the two exact buffer solutions that other devices would need to calibrate (usually 4.01 and 6.86). With the screw adjustment, you can use any value pH buffer solution.

The links below show the type of pH meter I am referring to. The Amazon.ca link is the exact pH meter that I use.

Amazon US

Amazon Canada

The pH level of your nutrient solution is important because it affects the availability and absorption of nutrients required for plants to grow. It determines how well each element of the nutrient solution passes through the cell walls of the roots. If the pH does not fall within the correct range, the roots will be blocked from absorbing nutrients and the plant will be starved, even if there is an abundance of nutrients available in the reservoir.

If the pH of the nutrient solution is too low or too high, you can use pH up or pH down to adjust accordingly.

I am currently using General Hydroponics pH up and down. If you can’t find it locally, check out the links below to find it on amazon!

Amazon US

Amazon Canada

Flushing means rinsing away excess salts and plant waste that have accumulated in the pot and reservoir over time.

When flushing, the pot is held under running water so that water runs through the pot and LECA and out through the drainage holes. This restores the chemistry of the pot and resets the media to salt free. Flushing should be done regularly, about every two weeks.

As water evaporates out of the nutrient reservoir, or is used by the plant, the concentration of minerals and salts in the pot will increase. Over time, if left to build to a high level, the excess salts can cause damage to the roots. This increased concentration can also adversely affect the pH level, impeding the plants ability to absorb nutrients and lead to deficiencies in the growth. Regular flushing is therefore important to restore the chemistry of the pot and reset the media to salt free. 

You’ll notice that the height of the nutrient reservoir will decrease due to evaporation and use by the plant. Consequently, as the reservoir depletes, the concentration of nutrients and salts in the pot will begin to increase, as water is being removed faster than nutrients. If you were to top up with more nutrient solution, the concentration of nutrients and salts already in the pot could become very high, adversely affecting the pH. I would therefore recommend using pH adjusted/distilled water with no added nutrients to help keep the pH and salt levels stable.

If you do not have pH up or down to adjust your pH level, you can use distilled water to top up your reservoir. Distilled water has a low and slightly acidic pH of around 5.8, which falls within the ideal pH range. Moreover, since the pH of the nutrient reservoir tends to increase over time as water depletes, using distilled water actually helps to prevent the pH from becoming too high.