Aeroponic Growing
By Erik Bicksa
I have adopted the following definition from Dr. Howard Resh’s Hydroponic Food Production (Fifth edition, 1995): “Aeroponics is the growing of plants in an opaque trough or supporting container in which their roots are suspended and bathed in a nutrient rich mist rather than a nutrient solution.”
There are a variety of manufactured aeroponic systems that have been developed and distributed to the indoor and greenhouse gardening enthusiast. They come in a variety of sizes, configurations and with various nutrient mist delivery systems. However, they tend to share some basic principles, as outlined in the definition of aeroponics.
Firstly, plants are not grown in a growing medium. Growing mediums would minimize the benefits and principles offered to growers through aeroponics. The plants do require mechanical support, which is most often provided by means of a flexible collar. This holds the plant in it’s rightful place in the growing system, suspending the root zone to the delivery of the nutrient rich mist. By eliminating the growing media and suspending the roots in the growing chamber there is more surface area available for root growth, thus increasing the surface area available for the absorption of nutrients, dissolved oxygen, and atmospheric oxygen.
As the nutrients for the plant are being sprayed onto bare roots, nutrients are readily available and are typically supplied from inorganic nutrients (synthetic fertilizers). There is no growing media to buffer pH or dissolved solids, so the rates of absorption can be extremely high. Also, the mist has a much greater surface area than conventional nutrient delivery systems (i.e. drippers), further increasing the rate at which nutrients may be taken up by the plant.
One of the biggest advantages that aeroponic systems offer versus conventional hydroponics is the level of atmospheric and dissolved oxygen that can be supplied at the rootzone to supercharge growth rates. In a very finely tuned closed growing environment, dissolved oxygen can become the limiting factor when using conventional growing methods. As the nutrient solution is delivered as a mist, the greater surface area allows more oxygen to be dissolved into the solution before reaching the plant roots. Also, as the roots are suspended in the growing chamber or trough, there is more atmospheric oxygen available to the roots versus plant roots that have been confined by growing medias and containers.
Aeroponic systems can be a difficult endeavor for the novice grower. However, a well manufactured system operated with care can be a very rewarding and easy growing method. As there is no growing media to contend with, it is tidy, with minimal clean up time between plantings. There is relatively no transplant shock, as the roots remain undisturbed when transplanting through the required growing stages. Best of all, aeroponic growing methods can offer production rates that you may not have thought possible.
In the last couple of years aeroponic systems have gotten to be more user friendly and more application specific. For this article, a commercially available home-use aeroponic cloning system (Power Cloner) was field tested. The test was very simple. The mother plants (see photograph) were heirloom tomato varieties (Black Russian) and were being grown hydro-organically in 2.5 Gallon Dutch Pots containing an organic planting mix in a roof top patio garden. The crop was started from seed in April and grown under natural light to subsequent planting outdoors (mid-May). The plants appeared healthy and had just begun to flower prior to removing donar material for the aeroponic production of cuttings. Cuttings were taken June 21st.
The aeroponic system took less than five minutes to set-up. The system came complete with:
- lower chamber (reservoir)
- upper tray with 45 plant sites
- spray manifold and connections
- salt water airstones
- air pump
- high-output submersible pump
- adjustable humidity dome
- neoprene supports
- tissue culture grade cloning solution (Power Clone)
- bio-fungicide (Hydroguard)
In this system, the bare stemmed cuttings were supported by hinged neoprene collars (45 sites) in a planting vessel measuring 16” deep X 24” long X 16” high. The inside of the growing vessel contained the high output submersible pump connected to the spray manifold. The removable (for cleaning) mist heads were pointed upwards towards the plantings (see photographs). Two airstones were submersed in the bottom of the growing chamber and were aerated via a high output air pump. Both the air pump and submersible pump ran constant, consuming negligible amounts of electricity.
After 24 hours of operation, the cloning solution and bio-fungicide were added to the system at the recommended rates prior to taking cuttings. Several days prior to taking cuttings, the mother plants received a solution containing organic carbohydrates (sugars), magnesium, trace elements, hormones, vitamins, and amino acids. Some research has suggested that cuttings may root quicker when the donor material has higher carbohydrate concentrations. If nutrients are over applied, cuttings may take longer to root.
The cloning solution was a commercially available tissue culture grade formulation that contained a balanced formula of macro and micro elements, vitamins, and root stimulator. The bio-fungicide contained a culture of beneficial life including several strains of Bacillus and a strain of Paenibacillus. Care must be taken when selecting nutrients and additives for aeroponic methods. The openings in the mist nozzles are very fine and may clog quickly with nutrient salts or other residues.
Upon final inspection, the mother plants appeared vigourous and free of insects or disease. Lower shoots were removed with a sterile disposable scalpel and immediately immersed in a dilute carbohydrate solution as described above. A few drops of the cloning solution were also added. If taking multiple cuttings, it is best to immerse the cut material in a mild solution as they may not be planted into the rooting system/tray quickly. Cut plant stems may acquire an embolism (air bubble) if not immediately planted or immersed once removed from the donar plant. Note that when not planting cuttings directly after removed from the plant, they will have to be re-cut, so longer stem material is recommended. The cuttings taken and planted were considerably larger than would have been taken with traditional rooting methods. The average stem once re-cut was about nine inches long with several sets of leaves remaining on the stem portion above the aeroponic system.
Once sufficient cut material was gathered and immersed, the material was ready for the final stage of preparation prior to transplanting into the system. Lower leaves were removed so that only a bare stem was in contact with the nutrient mist. Popular growing literature suggests ensuring that a node (stripped growth site) is present in the area where roots are desired.
Once lower leaves were removed, upper leaves were trimmed, and the base of the stem was re-cut with a sterile scalpel. The hinged neoprene collar was secured to the base of the cutting stem and transplanted into the system (see photographs). Again, good hygiene is critical. A sterilized food-grade cutting board and sterile disposable scalpel were used to prevent incidence of infection.
Once all the cuttings were prepared and transplanted into the system, the humidity dome was used to prevent excessive moisture loss from the relatively large cuttings. Ideally when cloning aeroponically, larger cuttings with more leaves can be used. If the cuttings root quickly and vigorously as intended, a significant amount of time for vegetative growth may be reduced. Ideally, the plants will be ready for transplant into flowering once sufficient roots have developed.
The cuttings were rooted under natural light, during the longest days of the year in this region. No significant maintenance or monitoring was required. The mist heads were inspected every couple of days to ensure they had not clogged. In this application, temperature becomes fairly critical. No climate control was implemented. Given the growing vessel was opaque white, it reflected most of the solar radiation away, keeping temperatures near optimal at 80°F. Although the temperature was a few degrees higher than optimal, it posed no visible problems. Keep in mind that good quality submersible pumps will heat the nutrient solution less than their oil-encapsulated counter-parts.
The results were unbelievable. Over 70% of the cuttings had a significant root system in seven days from transplant to the system. All appeared healthy. For most plants using conventional rooting methods, roots may form in seven to 14 days, but the rate and extent of their development was shadowed by this aeroponic rooting method. Given the size and health of the cuttings rooted in seven days, this application proved superior to conventional rooting in:
- percentage survival (100%)
- time to develop roots
- extent of root development
- size of rooted cutting
- number of healthy leaves per cutting
- maintenance required
- cleanliness
- clean-up time
- vigour of rooted plants
- no growing media to replace
The window of opportunity for insects, diseases, or other growing problems is reduced due to the shortened growing cycle.
In this particular growing situation, the rooted Black Russian tomato plants will be transplanted into several types of organic potting mix blends (another experiment that is intended to be shared with Maximum Yield’s readership). Keep growing, and don’t be afraid to try new things.