Source: http://www.genhydro.com/genhydro_US/quicktips/AeroHydroArticle.pdf

The aero-hydroponic method was developed in Israel in the early 1980’s. Dr. Hillel Soffer,
senior researcher at the Volcani Institute at Ein Gedi developed the aero-hydroponic method
to overcome the challenges presented by the hot, arid conditions at Ein Gedi. The discoveries
that followed the development of aero-hydroponics offer great benefits to all hydroponic
growers.

During a two-year period from 1986 to 1988, Dr. Soffer performed extensive research using
the aero-hydroponic method at the University of California at Davis, where he had received his
Ph.D. in the early 1970s. The specific area of research was in quantifying the effect of various
levels of dissolved oxygen on root growth, especially in the propagation of plants from
cuttings.

The findings of his research were published in the Journal of the American Society for
Horticultural Science, and HortScience. Both studies were co-authored with David Burger at
UCD. In addition, Dr. Soffer presented his findings at the annual conference of the Hydroponic
Society of America in 1988.
Except for the papers mentioned above, very little has been printed up to now on the aero-
hydroponic method. The method was patented internationally, though few licenses for the
production of equipment have been granted. Without aggressive commercial support, the
aero-hydroponic method has remained largely a research tool, known mostly to university
researchers.In the meantime, the rockwool method was becoming available internationally
following 12 years of exhaustive research and a strong marketing program with lots of
investment in advertising, production and distribution, first in Europe and later in Japan.
Following nearly a decade of rockwool use, the Dutch contacted Dr. Soffer to request
permission to develop and use the aero-hydroponic method. The reason for the sudden
interest of the Dutch in the aero-hydroponic method has implications for the development of
hydroponic cultivation worldwide.
For rockwool cultivation to work efficiently in most commercial operations it is preferred to a
use a non-recirculating nutrient solution. Nutrient solution is sent on a one-way trip through
the rockwool and is then discarded. The real cost advantage of rockwool cultivation over other
hydroponic methods was that the nutrient did not have to be recaptured and recirculated,
reducing the system complexity of reservoirs, plumbing, pumps and pH and conductivity
controllers.

The once-through nutrient system also reduces the problem of nutrient solution
becoming imbalanced due to erratic uptake of minerals by rapidly growing plants; plus the
build up of dissolved minerals from slowly dissolving rockwool.
The discharge of enormous amounts of spent nutrient solution has become a major problem
in Holland, contaminating surface and ground waters. Consequently, the Dutch government
has prohibited the dumping of nutrients resulting in renewed interest in recirculating systems
such as aero-hydroponics.
As leaders in both horticulture and commercial hydroponics, the Dutch have recognized the
value of a method, which enables rapid and trouble-free cultivation and eliminates the
problems of disposing of spent nutrients and exhausted media.

Aero-hydroponics is not a simple method to understand. The equipment required is

somewhat more complicated than other hydroponic methods, but there is a great advantage in
that once an aero-hydroponic system is set up, it will run almost indefinitely without additional
investment in such disposable components as growing media and non-recirculating nutrients.
What is most surprising about aero-hydroponics is not how it works, but why plants grow
better. The key is dissolved oxygen at the root boundary zone.

The essence of Dr. Soffer’s work at UCD was in quantifying root growth in proportion to
dissolved oxygen. Only the green parts of the plant can form oxygen from carbon dioxide -
roots require a supply of oxygen for metabolism and growth. Plant growth in oxygen deficient
conditions, such as those found in many soils, is limited. Dr. Soffer found the enhanced
oxygen at the root zone produced enhanced growth.

In aero-hydroponics, the nutrient solution is sprayed through the air in order to infuse the
nutrient with dissolved oxygen. The method differs from classic aeroponics in that most of the
plant’s roots are not suspended in air and fed by a spray of nutrient solution; rather, the
majority of the roots are submerged in oxygen-infused nutrient which is in constant motion in
order t maintain high levels of dissolved oxygen at the root boundary zone where oxygen and
nutrients are taken in by the plant.

The result is a propagating tool of unsurpassed performance. Dr. Soffer was successful in
propagating plant varieties at UCD that had never been propagated before. He took particular
delight in propagating varieties of conifers and even pistachio trees (pistachio cuttings
required 90 days to generate roots). Moreover, he found that cuttings could be rooted aero-
hydroponically in purified water without using rooting hormones such as IBA or NAA. This is
because plant tissue already contains the natural rooting hormone IAA (Indole Acetic Acid).

Aero-hydroponic systems can be built using quite a variety of materials and in numerous
design configurations. The Ein Gedi “Mini Unit” which was used at UCD for dissolved oxygen
studies is a stand-alone module which supports four plants in 10 liters of nutrient solution.
An electric motor mounted on the top of the unit spins a nutrient sprayer, which lifts nutrient
solution and sprays it onto the “aerial roots.” Additionally, the rotation causes the nutrient
within the unit to stir, moving it constantly over the submerged roots.

Large-scale aero-hydroponic systems follow the design of the commercial installation at Ein
Gedi. These commercial systems consist of “canals” or growing chambers with plant sites on
top. A pump provides the pressure to drive a system of sprayers to supply the aerial roots,
while the submerged roots hang into the flowing nutrient in the canal.

Both of these systems share fundamental characteristics, which define the aero-hydroponic
method. The plants are supported above the flowing nutrient. The roots hang down through an
air gap in which nutrient is sprayed, then into the moving nutrient solution below the air gap.
The nutrient sprayed through the air gap is not so much intended to feed the plant, but rather
to infuse oxygen into the nutrient solution wherein the feeder roots remain constantly
submerged. It is these submerged roots in oxygen rich nutrient that provides most of the
nutrition and oxygen for the plant.
Home Installation

The AeroFlo system is designed and built by General Hydroponics following the Aero-
hydroponic method. It consists of a reservoir placed below the growing chambers, which
support the plants. The nutrient in this system is changed every two weeks and the pH is
adjusted to 5.5 to 6.5 and nutrient conductivity is maintained at about 800 to 1200 ppm.
Since there is no growing medium except a handful of “GROROX” at each plant site, pH
remains very stable and only requires an initial adjustment when mixing fresh nutrient, if the water supply is of good quality.

The AERO-HYDROPONIC METHOD is without doubt the most advanced hydroponic method
that has been developed to date. The cost of constructing and installing systems, plus the
complications of obtaining licensing, have been deterrents to widespread commercial
application. This is changing as commercial growers, researchers, serious hydroponic
gardeners and manufacturers become aware of the capabilities and value of aero-hydroponics.

Lawrence L. Brooke is the owner and founder of General Hydroponics in Sebastopol, California
Originally published in The Growing Edge, Vol 2, No 1, Fall 1990

Recently at the International Master Gardener’s Conference a speaker, Dr. Dave Lipschitz addressed the attendees with his talk: Gardening: A path to a long and independent life. He mentioned that statistically, only 1 in 2 people above the age of 85 are able to live independently and that in the next 20 years the number of people 85 and above will triple. He said that gardening was an important component of staying healthy. Not only does gardening provide a spiritual connection, there is a link to healthy eating and the exercise component, which is the key to longevity. I used to snicker as a kid when my mother would tell me that gardening was good exercise. I didn’t understand how a leisure activity could be considered exercise. Where was the sweat? Where was the heavy lifting? Well, that was before my mother or I owned a greenhouse and before container gardening became a mainstay. I have newfound respect for the gardeners of the world; especially those who own a greenhouse.

Having a greenhouse is like going to a buffet where eyes are often larger than the stomach. With a greenhouse it just takes longer to realize your plate is full. Seeds look so tiny and unassuming. Who would know that when planted and given a happy home, they grow into unruly giants? When starts are in need of transplanting or a permanent home in the garden is when the work out begins. Those seedlings grow and grow. Pretty soon you have enough planting to keep you busy for weeks.

When we garden in a greenhouse we take a lot for granted; most obviously a pleasant environment. It doesn’t rain in a greenhouse unless you want it to, and the temperature is usually more pleasant than outdoors. In early summer, transitioning from greenhouse gardening to gardening outdoors involves more changes than the weather. If you’ve been gardening in your greenhouse through the winter or even just this spring, you may not realize that you too may need a slight transition back to outdoor gardening. Just as you place your greenhouse plants in a protected area to harden them off before planting; it’s not a bad idea for people to approach the change in the same way.

Greenhouse gardeners don’t miss a beat when the weather turns cold in the fall. They quickly adapt to a new environment. Come summer, it’s easy to forget that a greenhouse offered more than protection from the cold. There are doors to keep many of the biting and stinging insects out. There is covering to protect you from the sun’s UV rays. The floor is even and stable, no rocks to twist ankles or to trip on. Benches prevent stooping and bending for planting or caring for over winter guests. Scooping replaces digging. Fans exhaust the hot air when it gets too warm. Weeding consists of plucking out unwanted residents rather than excavating them. Plants start as small seeds rather than large pots. The unassuming greenhouse gardener doesn’t realize a transition awaits them.

Dr. Lipschitz did not mention that roughly 400,000 people visit the emergency room each year for gardening related injuries or that it’s estimated that one in five DIY injuries are garden related. Most of these injuries are preventable. If you’ve transplanted the equivalent of a small nursery, perhaps you’ve experienced common gardening injuries; strained muscles, sunburn, heat stroke, or repetitive stress and fatigue.

Many of these injuries are avoidable with a few precautions. First of all, when transitioning to the garden from the greenhouse, give yourself a little time to ease back into the outdoor routine. Before starting any intensive work, go for a five minute walk to get the blood flowing. Next, do some light stretching but don’t push yourself when your muscles are cold, just do light stretching to limber up. Secondly, don’t expect to get everything done in one or two sessions. Give your muscles time to adjust to new positions and stresses.

Proper body mechanics is important to maintaining an injury free summer. If you’ve been growing in your greenhouse, chances are you’re used to working on benches. It’s a whole new story when you start to work at ground level. Maintaining a strong core will go a long way to keeping the rest of your body healthy. When lifting arms, legs or engaging your back, keeping your stomach muscles engaged will protect the back muscles. Many of us were told to “suck in your stomach”; however, it’s more effective to stick your stomach out slightly
.
Think about your reflexes as someone punches you in the gut. That constriction in your stomach is the position you want to maintain. If you are lifting anything or stretching your body to reach a particular place, be mindful of your core muscles. Keeping your stomach tight will protect your back which is prone to injury. When lifting heavy objects, lift with your legs and make sure to keep the object close to your body. If you are moving heavy containers into or out of the greenhouse, get some help. The PotLifter is an inexpensive tool that distributes the weight evenly making awkward loads easy to move with the help of someone else.

Using the proper tools will also go along way in preventing injuries. Raised beds provide an excellent environment for plants and reduce much of the bending and stooping of a traditional garden. If you are working at ground level for long periods of time, use a kneeling pad, knee pads or a garden rocker to elevate stress on your lower back. New ergonomic and light-weight Radius tools reduce repetitive stress injuries while digging, weeding and transplanting. By keeping your wrist in a neutral position, these new tools help you get the job done with a relaxed and natural grip. Bionic gloves (www.bionicgloves.com) are also a wonderful tool in the garden. Reinforcement pads in the fingers make gripping easy while reducing strain and pressure points on your hands.

In summer we strive to keep our gardens well fed and pest free. It is also when we see a dramatic rise in chemical injuries. Labels on pesticides, fertilizers and garden products are not just instructions, they are a legal contract. Following the directions on packaging is the only way to ensure your safety, so read labels carefully. Also keep chemicals out of reach of children. Summer is the perfect time to clean and disinfect your greenhouse. Before you use chemicals or cleaners to disinfect your greenhouse, check with the manufacturer to determine what products are safe with your covering. Some cleaning chemicals react with various materials and may produce hazardous gasses when applied to the wrong surface. Also keep body mechanics in mind when cleaning your greenhouse. Don’t forget to bend at the knee and be careful to keep your back in a neutral position (the lower back muscles are not engaged) when cleaning the lower portions of the structure.

Regardless of how you use your greenhouse, you’ll have plenty to do all year round. Use these safety tips and you’ll enjoy the rewarding and relaxing benefits of gardening for the seasons and for many happy years to come.

This article was originally published in Garden & Greenhouse Magazine. Garden & Greenhouse is written for small commercial growers, hobby greenhouse owners and indoor/outdoor gardeners and is free to qualified readers. For more information visit http://www.GardenAndGreenhouse.net .

Once you have selected and isolated a space, cover the walls with a highly reflective material such as flat white paint or reflective mylar. Reflective material will significantly increase the amount of energy available to plants by reflecting more light onto your garden. You should keep airflow constant with one or two oscillating fans, but be sure fans don’t remain in a fixed position for too long as this can cause windburn, or dry out young seedlings. While an open door or window may do the trick, you can use an exhaust fan attached to a thermostat to bring in fresh air while venting hot, humid air out of your growing space. You can also vent warm air from your indoor garden to other areas of your house to reduce your heating costs during cold seasons.

A 10-by-10-foot garden may need as much as 30 gallons of water per week, which you can easily supply with a hose in the room with an on/off valve attached to a spigot or faucet inside the house. This will be a year ’round operation, however, so don’t plan on running a hose from an outdoor spigot. Watering wands help to reach all your plants easily, and prevent the breaking of branches when watering dense foliage. While it can be helpful to have a hot and cold water source in your garden to regulate water temperature, please note that hot water pipes contain calcium and lime which can cause significant pH shift in your hydroponic reservoir. Many hydroponic gardeners never use hot water, but instead fill a large container with water from the cold tap and heat it with a reservoir heater before adding it to their nutrient reservoir.

Light movers don’t increase the coverage area of your light but significantly improve the dispersal of light throughout your garden. You should mount light movers securely in a level position. If you want your lamp to remain stationary, mount it on one or two ceiling hooks strong enough to support about 30 pounds. Your light should be in the middle of the growing area for maximum coverage. Use a chain or a rope and pulley to adjust the height of the light; this also facilitates moving the lights out of the way for watering and maintenance.
With everything in place, you’ll be ready to move your seedlings or rooted clones into the room. Huddle the plants closely, about 24 inches from the lamp, making sure the light won’t burn their leaves. Thin young plants as they grow and develop to give them the room they need so that the healthiest, most vibrant plants can thrive without interference from their weak, pest and disease-prone siblings.

NOTE: It’s extremely important to keep your lamp dry! A hot HID bulb may break if it comes into contact with just a few drops of water. In general, handle your lamps with care. These small, intense light sources can burn your plants if not positioned correctly, and can be electrical and fire hazards if not properly installed. While you don’t have to be a professional electrician, or even hire one, to set up your indoor garden, consulting one can save you time and money. There are many different types of lamps and bulbs; be sure that your lamp meets your needs, as well as the needs of your plants.

The aeroponic system is probably the most high-tech type of hydroponic gardening. Like the N.F.T. system above the growing medium is primarily air. The roots hang in the air and are misted with nutrient solution. The mistings are usually done every few minutes. Because the roots are exposed to the air like the N.F.T. system, the roots will dry out rapidly if the misting cycles are interrupted.

A timer controls the nutrient pump much like other types of hydroponic systems, except the aeroponic system needs a short cycle timer that runs the pump for a few seconds every couple of minutes.

This is the kind of hydroponic system most people think of when they think about hydroponics. N.F.T. systems have a constant flow of nutrient solution so no timer required for the submersible pump. The nutrient solution is pumped into the growing tray (usually a tube) and flows over the roots of the plants, and then drains back into the reservoir.

There is usually no growing medium used other than air, which saves the expense of replacing the growing medium after every crop. Normally the plant is supported in a small plastic basket with the roots dangling into the nutrient solution.

N.F.T. systems are very susceptible to power outages and pump failures. The roots dry out very rapidly when the flow of nutrient solution is interrupted.

Drip systems are probably the most widely used type of hydroponic system in the world. Operation is simple, a timer controls a submersed pump. The timer turns the pump on and nutrient solution is dripped onto the base of each plant by a small drip line. In a Recovery Drip System the excess nutrient solution that runs off is collected back in the reservoir for re-use. The Non-Recovery System does not collect the run off.

A recovery system uses nutrient solution a bit more efficiently, as excess solution is reused, this also allows for the use of a more inexpensive timer because a recovery system doesn’t require precise control of the watering cycles. The non-recovery system needs to have a more precise timer so that watering cycles can be adjusted to insure that the plants get enough nutrient solution and the runoff is kept to a minimum.

The non-recovery system requires less maintenance due to the fact that the excess nutrient solution isn’t recycled back into the reservoir, so the nutrient strength and pH of the reservoir will not vary. This means that you can fill the reservoir with pH adjusted nutrient solution and then forget it until you need to mix more. A recovery system can have large shifts in the pH and nutrient strength levels that require periodic checking and adjusting.

When the timer turns the pump on nutrient solution is pumped into the grow tray. When the timer shuts the pump off the nutrient solution flows back into the reservoir. The Timer is set to come on several times a day, depending on the size and type of plants, temperature and humidity and the type of growing medium used.

The Ebb and Flow is a versatile system that can be used with a variety of growing mediums. The entire grow tray can be filled with Grow Rocks, gravel or granular Rockwool. Many people like to use individual pots filled with growing medium, this makes it easier to move plants around or even move them in or out of the system. The main disadvantage of this type of system is that with some types of growing medium (Gravel, Growrocks, Perlite), there is a vulnerability to power outages as well as pump and timer failures. The roots can dry out quickly when the watering cycles are interrupted. This problem can be relieved somewhat by using growing media that retains more water (Rockwool, Vermiculite, coconut fiber or a good soiless mix like Pro-mix or Faffard’s).

The water culture system is the simplest of all active hydroponic systems. The platform that holds the plants is usually made of Styrofoam and floats directly on the nutrient solution. An air pump supplies air to the air stone that bubbles the nutrient solution and supplies oxygen to the roots of the plants.

Water culture is the system of choice for growing leaf lettuce, which are fast growing water loving plants, making them an ideal choice for this type of hydroponic system. Very few plants other than lettuce will do well in this type of system.

This type of hydroponic system is great for the classroom and is popular with teachers. A very inexpensive system can be made out of an old aquarium or other water tight container. We have free plans and instructions for a simply water culture system.

The biggest draw back of this kind of system is that it doesn’t work well with large plants or with long-term plants.

The Wick system is by far the simplest type of hydroponic system. This is a passive system, which means there are no moving parts. The nutrient solution is drawn into the growing medium from the reservoir with a wick. Free plans for a simple wick system are available (click here for plans).

This system can use a variety of growing medium. Perlite, Vermiculite, Pro-Mix and Coconut Fiber are among the most popular.

The biggest draw back of this system is that plants that are large or use large amounts of water may use up the nutrient solution faster than the wick(s) can supply it.