The Ebb & Flow Method of Hydroponics [from the archives 2012]
HYDROPONICS INTRODUCTION: Why Soil-less Gardening?
Soil is very complex. It’s an entire living community, forming a whole web, with trillions of microorganisms such as bacteria, fungi, as well as worms and arthropods (insects etc.) that break down the organic material, in concert with the enzymes from the roots of plants, to convert it to nutrients like Potassium, Phosphorus and Nitrogen. These basic elements are absorbed as ions, via water, by plant roots.
All plants need 17 elements to grow. They are:
Macronutrients derived from air: Carbon (C), Hydrogen (H), and Oxygen (O),
Macronutrients derived from ions in the soil, Nitrogen (N), Phosphorus (P), Potassium (K), Sulfur (S), Calcium (Ca), and Magnesium (Mg),
Micronutrients derived from ions in the soil, Boron (B), Chlorine (Cl), Copper (Cu), Iron (Fe), Manganese (Mn), Molybdenum (Mo), Nickel (Ni), and Zinc (Zn).
Elements derived from the atmosphere are from the plants breathing via leaves and roots. Plants breathe in CO2, Carbon dioxide, and through the miracle of using sunlight, water, chlorophyll, turn it into food, such as sugars and starches (carbohydrates) and proteins for themselves and animals. Plants however cannot directly utilize Nitrogen, which is needed to make proteins and amino acids and countless other chemicals found in plants.
Organic material such as wood and dead leaves contains Nitrogen and other basic elements, but they cannot be absorbed directly by plants: they need the help of fungi, bacteria and other consumers to process dead plant, animal and minerals and turn them into plant food for green plants. Complex substances from dead plants and animals like proteins and fibers have to be broken down with the help of this community of organisms to make those bound-up elements available to green plants. It turn, the green plants provide food for the community in the soil (and on land and air!) in a continuous cycle of living metabolic activity, powered by cosmic energy from our star the Sun.
In hydroponics, we are in a sense short-circuiting this process, taking a direct approach and giving plants those nutrients, and only those nutrients, those ions in water directly, and abundantly.
The word “hydroponics” comes from the Greek words “hydro” meaning “water”, and “ponein”, “to labor or toil”. The first experiments in finding out what plants actually need – the elements of the period table (N,P,K, just as you see on any fertilizer package) – were done in pure water, with no soil, and mineral salts such as Potassium nitrate added to form ions of the elements that plants could absorb.
Hydroponics is part of “controlled environment agriculture”, based on the knowledge of optimum conditions for plant growth that have been isolated and identified. Systems are created to give the plants directly and exactly what they need for maximum growth. Very high growth rates, large size, and healthy plants with no pests or diseases are often the result of using hydroponics. There are few pests because healthy plants have a natural immunity. Pests attack weak plants, and properly grown hydroponic plants are very strong.
Other aspects of controlled environment agriculture include greenhouses, where temperature, humidity, air circulation (and even gas composition) can be controlled to some degree to help optimize conditions for year-round growing. Hydroponics in particular started with the discovery that plants could be grown in water and derive the mineral nutrition they require with a precise feeding of mineral salts to supply the roots with their required elements. Since that discovery, many variations of hydroponics have been invented, including organic hydroponics. However, they all use the basic method of using water, rather than soil to deliver nutrition to the roots.
Solution Culture – plants are grown in straight nutrient water solution with no “soil” for support:
Static (aerated or not)
1. Raft Solution Culture
2. N.F.T. (Nutrient Film Technique / Continuous Flow)
Medium Culture – plants have a supporting medium physically acting like soil:
4. Wick System
5. Drip Systems Recovery / Non-Recovery
6. Ebb & Flow
A PDF that explains these six basic techniques can be accessed here.
THE BASIC EBB AND FLOW TECHNIQUE
The Ebb & Flow (also known as Fill and Drain) technique of growing plants hydroponically is a low-tech method that has been around for many years. The advantages are simplicity, relatively low investment, and reliability. It does not take any fancy equipment, just a bit of initial work to set up the system. Once it’s set up, you will get tremendous growth, and can grow a very wide variety of plants, large and small, because it mimics an ideal soil medium. It also provides a support for larger plants. I’ve grown everything from lettuce to corn, tomatoes, peppers, squash, broccoli, and many kinds of herbs. One of the advantages is the amount of air exchange with the roots. Plants grow vigorously with the good gas exchange that happens with this method, and are able to get high levels of water and nutrients from the medium.
The basic idea is very simple. A tray or bed is filled with a course growing medium. A nutrient solution gets pumped into a growing tray, almost to the top of the medium. Excess water drains out of the drain stop, recirculating for a short time until the pump switches off. Once the pump is off, the nutrient drains out, leaving the medium flush with nutrients and water, and pulling air down into the medium (the root zone) in the process. This is done generally twice a day but can be at whatever regular interval is required. With highly water-retentive media in relatively cool conditions, watering only once a day is enough. By contrast, something like a gravel system, which does not retain as much moisture, could be flooded every hour in warm weather.
LET’S GET STARTED
OK, so let’s go over all the basic components.
First you need a growing bed. Something that is watertight. The bed in the photo at the top of this article was made from wood and lined with fiberglass. It also needs to be strong enough to hold up the weight of water and a growing medium. A growing medium (the “rocks”) is what holds the plants up.
Deeper beds are better for larger plants. Roughly 4 to 8 inches is usually enough. The growing bed in the photo at the top might have been deeper, because I used 2 by 12 planks of wood for the sides (which are actually 1.5″ x 11.25″).
Almost any container or tray that will hold water and a growing medium can be used. I’ve used various kinds of ready-made trays found at hardware stores. I’ve also used other containers such as a 5-gallon bucket or a discarded 5-gallon water jug. It must have a drain hole too.
At one end of the bed you need a drain hole. However, you don’t want the medium washing out as the nutrient solution drains. You also want the nutrients draining at a proper rate: too slow and the roots would get water logged, too fast through large holes and it won’t fill the bed, and might disturb the root hairs or wash away medium.
In the herb beds in the following photo, I used a c-clamp to control flow back into the nutrient tank. I probably just had a simple screen over the drain hole.
In the large beds I’ve used a simple PVC pipe or tube with holes drilled into it, stuck into a hole in the bottom of the grow bed. I then used silicone or epoxy to seal it in. When water gets to the top of the pipe, it drains fast through the end hole, thus preventing the level from rising any further and over-filling the bed.
You also need a screen around the drain tube so that medium doesn’t plug up the holes in the tube and to assist in draining.
The holes of the mesh have to be small enough such that the medium doesn’t wash though the holes. Metal window screen, painted with epoxy paint will do the trick. It might need a thicker mesh, such as 1/4″ or larger, to support it. You will want to glue or somehow fasten the mesh circle to the bottom of the bed so that it doesn’t move around. The type of glue you use depends on the composition of the bed. A plastic bed such a concrete mixing tray may requite special plastic glue, as silicone or most epoxies will not stick to it.
Be sure to make the top of the drain tube low enough so that the nutrient drains from the top of the tube and recirculates before reaching the top of the medium. You don’t want the plants floating away! (See diagram)
You will want to tilt the bed slightly so that the nutrient solution drains completely. This principal is important: you do not want any standing water. This can lead to fungal growth, root rot, and lack of oxygen.
THE GROWING MEDIUM
The growing medium’s function is to support the roots and the plant, hold moisture and nutrients, and allow air circulation. You don’t want a medium that holds too much moisture (for example straight vermiculite) because you will get organisms growing such as fungus, and algae on top, and not enough air exchange. Roots literally breathe, and oxygen and carbon dioxide gas exchange is crucial for healthy and vigorous plant health and growth. Coarse gravel, sand and perlite are examples of mediums that do not hold enough moisture. They dry out too fast and do not retains nutrients for the plants very well. They drain quickly however.
I’ve had great success with white pumice (which just happened to be available at a local nursery). It drains quickly but also holds moisture and nutrients. Expanded clay (sold as “Hydroton”) has similar properties but is lighter weight than pumice (which is good), as does lava rock. These are popular and work well.
Another factor to consider is the weight of the medium and how much your bed can support.
Various materials have been used by growers over the years, including gravel, volcanic rock, sand, perlite, vermiculate, and various kinds of commercially created aggregates (such as Hydroton expanded clay).
I’ve used combinations to get the right kind of weight and moisture retention. For example, a mixture of perlite and vermiculite, or perlite and polymer water crystal beads is very light weight, and good for small beds. The drawback of an extremely light weight medium is that it can’t provide a great deal of support for a large plant, such that a heavy or tall plant could potentially fall over when it gets large.
THE NUTRIENT SOLUTION
Hydroponic nutrients is a huge topic. I’ll just give the briefest of outlines and tell you what I used. The essential idea with hydroponics – which literally means water work – is to provide exactly and only what the plant needs in terms of basic elements. Early researchers who were trying to find out what plants actually get from soil – their minimum and essential needs – grew plants in water, and found out by trial and error that all green plants need just a few basic chemical elements from the periodic chart: mainly Nitrogen, Phosphorus, and Potassium. They also need a range of “micronutrients” – metals such as iron and magnesium, in extremely small quantities. They absorb these as dissolved minerals – ions – from the water in the root zone. In nature, these elements come indirectly, from the breakdown of a large array organic materials and rocks, through very complex biological and inorganic processes. Hydroponic methods supply these elements directly, in the form of mineral salts. (Newer methods also use organic solutions – a more complex and difficult technique, needing it’s own chapter).
A salt, when dissolved in water, breaks into the constituent ions. For example, Potassium Nitrate dissolves into Potassium ions (K+) and Nitrate ions (NO3). These are what the root hairs absorb in the water.
Hydroponic nutrients are supplied to the grower in the form of powders or concentrated liquids. Because some of the salts will react with each other and form precipitates (solids) or other combinations that you don’t want, they often come in the form of more than one solution.
The nutrients that I have experience with were from General Hydroponics. I had excellent results. Commercial growers and NASA use them. They were FloraGrow and FloraBloom.
THE NUTRIENT TANK
For the ebb and flow systems in the photos, I used a plastic trash can. Any container that is large enough for the estimated capacity, will fit below the level of the growing bed (since it’s gravity fed), and will not react with the nutrients will suffice. Avoid metal containers, as they could potentially react chemically with the salts in the nutrients. You will want something with a cover too – animals or insects and debris can get in your tanks. I once had a hydroponic system on top of a trellis outside my bedroom window in Del Mar, California. The nutrient tank was similar to the bed: a large rectangular tank that fit under the bed. Tree frogs got in it, attracted to the water, and made quite a racket at night!
THE PUMP and FITTINGS
I used submersible fountain pumps available at hardware stores and nurseries. There are a range of sizes available, rated in Gallons Per Minute (GPM). You want to find one with enough capacity for your system, but not so large that it’s going to create too much flow. You might need an inline valve to control flow. Some of the fittings for tubing and to create a bottom nozzle or drain on a trash can (if needed) were obtained at a Koi pond supply store.
The timer for the pump was an ordinary appliance timer. You can also use a digital timer. Just make sure whatever you use has enough rated wattage to run your pump. I built a box underneath the bed to keep the timers and plugs organized and away from the elements, as you can see in the following photo.
The use of a large amount of an aggregate medium means that you will need to clean the medium at the end of a growing season, or at some point, or replace it. This washing is necessary to remove root debris, and possibly precipitates from the nutrients. You may want to also sterilize the medium. How often this needs to be done depends on the condition of the medium and how many plant roots are left behind after harvesting or season’s end.
Another possible drawback is that different plant root systems can get tangled together, making them harder to separate.
Overall though, every technique has it’s drawbacks, so you have to look at what you want to grow and what kind of investment you want to make, what fits your needs and budget, and what appeals to you.
Ebb and Flow hydroponics is a worthwhile technique for those on a budget, and wanting to create a significant growing space for a wide range of crops. It’s a fun way to grow vegetables, herbs and flowers, and is the closest to growing in soil of any of the methods. Using simple materials, an extremely vigorous and fast growing garden can be created – one with few pests (healthy plants have strong immune systems) and no weeds. HAVE FUN!