Hydroculture: Growing plants without soil

There are other ways to grow plants than with soils. In fact, there have been advances in the ways people can grow plants and flowers using mediums other than soil and standard growing mediums.

These methods use less water because they use substances other than standard water and growing mediums.

One of the methods that people know about is hydroponics, which grows plants in a liquid solution without the use of soil. The other is called hydroculture, and that is similar but also very different at a fundamental level.

We asked the Ambius Plant Doctor to explain what hydroculture is and what the benefits of using this growing method are for indoor plants.

What is hydroculture?

The term “hydroponics” is familiar to most people. Hydroponics involves growing plants in a liquid growing medium solution. Hydroponics has become quite popular in recent years, particularly in the growth of vegetables like lettuce and tomatoes.

Hydroculture is similar to hydroponics in many ways but has a key difference – instead of using a nutrient solution containing water as a growing medium, it uses an inorganic solid growing medium (or inert).

The inert growing medium is usually rock-based, typically something called “expanded clay aggregates.” Hydroculture is sometimes called “passive hydroponics,” meaning the plants grow without soil, bark or peat moss.

What are clay aggregates? What is LECA?

The clay aggregates – often called LECA (Lightweight Expanded Clay Aggregates) – are small pieces of clay. The small clay pellets are heated to very high temperatures in rotating kilns. The extreme heat causes the clay particles to expand, somewhat similar to popcorn popping. As it expands, the pellets lose density and develop many air pockets inside. The end product is marble-sized aggregates that look similar to Cocoa Puffs cereal.

Other versions of LECA may have a different appearance depending on the sources of clay and the process by which they are produced. These clay aggregates become the growing medium.

What makes LECA an ideal growing medium?

LECA has three very desirable growing properties:

1. It is extremely porous. This provides abundant air and oxygen to the roots of plants. Lack of oxygen is a major cause of plant loss, particularly for interior plants. The healthy roots are less prone to disease and rotting.
2. It has capillary properties. This means that dry LECA absorbs water and wicks it upwards (often 8-10” upward or more) to provide water to the plants.
3. It does not compact or decay over time (organic-based soils do). This helps aid in the delivery of air to the roots of the plants.

Because of these three properties, LECA can deliver ample water and nutrients to the roots of plants while simultaneously providing abundant oxygen to the root zone. This makes for an ideal growing environment for the plant roots.

The roots of a plant are critical to the overall health of a plant and a healthy root system will yield a healthy plant. Conversely, a weak root system will weaken and shorten their lifespan.

What is the advantage of clay aggregates over normal organic soil?

The biggest advantage is the abundance of air to the roots, leading to a very long-lasting, healthy root system. Typical organic soils (peat moss, coconut choir, etc.) break down and decompose over time, reducing the desirable growing qualities they initially. They are also prone to compaction. These factors reduce air, water and nutrient availability to the roots.

Organic-based soils can also be quite difficult to water since as the plant and the soil age they are easy to over-water. When they get too dry (particularly peat moss), they will often shrink and may become hydrophobic, making them difficult to re-wet and absorb moisture.

Organic-based soils have their uses such as providing a very good growing medium for establishing plants (for example when the plants are actively growing at the grower or nursery stage.)

How does hydroculture work?

Most hydroculture plants are grown in typical organic soils such as peat moss. When a developed root system has established itself, this soil is removed. The removal process initially involves removing the remaining soil, typically with high-pressure hoses or power washers.

The resulting bare root ball is put back into a growing container and LECA is poured in around it, replacing the soil. The plant is then watered to allow several inches to accumulate in the bottom of the LECA. This water is wicked upward and delivered to the roots of the plant.

The removal of the soil and replacement with LECA can cause shock and stress to the plant. Some plants show few signs of stress whereas others may drop some leaves, droop, wilt, etc. Ideally, plants are “hardened off” in a greenhouse to allow them to acclimate to the new growing medium.

Once the plants have acclimated to hydroculture, they are relatively easy to care for. Many hydroculture plants can go more than six weeks until the next watering.

Watering is quite straightforward – typically it only involves adding an inch or two of water to the bottom of the container. Small water meters are helpful as they show how much has been added to the container.

What are the main advantages of hydroculture?

The following are the main benefits of hydroculture:

1. No fungus gnats. Interior plants are notorious breeding grounds for small flies called “fungus gnats.” Although not harmful to the plant, fungus gnats are incredibly annoying to people and quite difficult to control. They thrive in moist or damp organic matter and more typical soils provide this environment, which is why fungus gnats are so common on soil-based plants. LECA is an inorganic (rock-based) growing medium and fungus gnats cannot reproduce or thrive in this environment, thus are non-existent with hydroculture plants.

2. Less guesswork when watering. Watering interior plants (including houseplants) can be a tricky task to master. Soil-based plants have to be watered with a lot of precision and know-how. One of the most common and easiest mistakes made with soil is over-watering. When plants are watered too frequently or too much at one watering, soils become water-logged, depriving the roots of oxygen. This causes the roots to fail, thus causing stress and premature death to the plant.

With hydroculture, it’s still possible to over-water or under-water plants but the margin for error is greater. The abundant air present in the LECA enables a stronger root system that is also more forgiving if over-watered.

3. Longer watering cycle. The frequency at which interior plants need to be watered varies based on many different factors; however, the average watering cycle for a 6” plant is probably every 2 weeks in soil. With hydroculture, the length of time between watering is typically tripled.

A 6”  hydroculture plant can typically go six weeks or more without having to be watered again. This can be especially helpful for people that cannot access their plants every two weeks (i.e. away from home, vacation, etc.).

4. Longer-lasting plants. Hydroculture is the ideal growing medium for interior plants because the roots are healthier and more robust. Healthy root systems support longer-lasting plants.

Is hydroculture a new thing?

No. Hydroculture has been in practice for decades, particularly in Western Europe. Many interior plants and houseplants in Western Europe are sold as hydroculture plants.

Why is hydroculture not common in the United States?

This primarily has to do with the supply chain. Growers must have buyers of their plant material when the crop cycle finishes. Currently, there isn’t enough demand to justify the growth of hydroculture plants. Much of this has to do with a lack of knowledge about hydroculture, including on the consumer end. For example, if a consumer bought a hydroculture plant, they would need to know how to properly care for it. Although this is a hurdle, hopefully, it can be overcome over time. In the short term, we’re stuck with soil-based plants.

Can you convert your own plants to hydroculture?

Yes. However, the level of success varies based on a variety of factors (type of plant, size of plant, skill, etc.). In general, it is easier to convert smaller plants than larger ones. Good starter plants include 6” Aglaonema, Dracaenas and Pothos. Start with new plants direct from a garden center. Converting older and larger plants is difficult.

If you convert your own plants, expect an acclimation period, typically lasting 1-2 months. This frequently involves a few yellow leaves and other symptoms.

How long will a hydroculture plant last?

It varies but it’s not uncommon for a hydroculture plant to last ten years or more.

Although a tougher, more resilient plant, they will still need adequate light, water, nutrients, etc.

Why isn’t hydroculture more common?

Currently, hydroculture is more common among plant hobbyists who have converted their own plants. Hydroculture would be much more common if consumers could purchase the plants already converted. The conversion process (particularly the soil removal) can be quite messy and cumbersome to do in-house. Additionally, most people are unaware of hydroculture or how it works.

Are hydroculture plants the same thing as hydroponic plants?

No. Although there are some similarities between hydroculture and hydroponics, these are not hydroponic plants because the roots are not constantly suspended in a liquid solution. This is very important to know because the most common mistake people make with hydroculture is over-watering the plants, such as filling the entire growing medium with water and displacing all air.

Air in the root zone is critical to making hydroculture work properly.

Green Side Up,

Matt Kostelnick, Senior Horticulturist at Ambius