Seedling production has changed greatly over the past 50 years, and its potential for the future is looking bright as ever.

Some 50 years ago, the standard method for producing vegetable seedlings for transplanting was to sow the seed in a nursery bed and then dig up the seedlings when they were large enough to be successfully transplanted. The system was anything but fool-proof; in fact, it provided an ideal means of distributing soilborne pests and diseases (that were present in the seed bed) over a larger cropping area. This was overcome by many brassica seedling growers by fumigating the soil with a chloropicrin/methyl-bromide mixture some months prior to sowing the seed. This method also provided some weed control as a by-product.

In the 1970s, the use of cell trays for growing vegetable seedlings was developed. This provided a means of mass-producing seedlings for later planting in the field by supplying water and nutrients via overhead booms and having the roots air pruned. For the past 20 years, it has become a common practice for vegetable seedling producers to germinate the seeds—after sowing in cell trays—in special temperature-controlled rooms to ensure better and more even germination.

It is now timely to consider the potential for growing seedlings (until transplantation) in a totally environmentally controlled room—in which nutrition, water supply, temperature, day length, light intensity (and wavelength), humidity and levels of carbon dioxide are precisely controlled. Using such technology, it should then be possible to produce perfect vegetable seedlings at any time of the year without reference to the outside conditions. It might also have the potential for a very fast throughput, as it might be possible to produce seedlings using a 24-hour day. Thus, producing quality seedlings would be greatly simplified.

Also, such a system would also reduce the amount of variation currently occurring in conventionally produced vegetables crops (if 50% of the plants life is spent in controlled climate conditions, then any variation in the weather in the field after planting will have a much reduced impact on time to maturity). Still, the shorter time the plants are exposed to variable weather conditions, the more precise you can time crop maturity. As such, a further advantage of plant factories would be the potential to hold plants if planting conditions in the field are not satisfactory. This might involve no more than simply reducing the temperature (an action that is much harder hard to achieve in a greenhouse than in a plant factory because it is very difficult to reduce either light intensity or temperature in a greenhouse; thus, to hold young seedlings in a greenhouse, you have to ventilate, supply the seedlings with no fertilizer and keep the watering levels low—a sub-optimal solution).

An additional factor (following the necessary research) would be to develop a technology that would prepare the plants beyond standard hardening-off in order to assist the plant in rapid growth after transplanting. This might be a simple as feeding the plant with nutrients and dropping the temperature, but not the light intensity, so the plants become loaded up with carbohydrates and inorganic nutrients.

Grafting plants is becoming increasingly important for high-value crops, such as tomatoes and cucurbits, so the production of more even rootstocks and scions, and the ability to provide a very precise environment for the germination stage, the graft union process and for the growing on stage has real potential. The high value of these plants makes plant factory technology very relevant for the present, let alone for the future.

In September 2012, there was a major international workshop at the University of Maryland on the challenges in vertical farming. The motivation for this meeting was stated by the organizers as follows:

By the year 2050, we expect human population to increase to 9 billion and to be further concentrated in urban centers. An estimated billion hectares of new land will be needed to grow enough food to feed the earth. At present, however, over 80% of the land suitable for raising crops is already in use. Further, if trends in climate change persist, the amount of land available for farming will decrease. Since crops consume 87% of all water used globally, an increase in water usage is not possible. Finally, while the need is for 50% higher yield by the year 2050 to maintain the status quo, we expect agricultural productivity to decline significantly across the world, especially in densely populated areas. There is an urgent need for high-yield agriculture that decreases the use of water and carbon based [sic] inputs per unit of product, while simultaneously reducing vulnerability of crops to natural environmental conditions.

Whether plant factories are a suitable vehicle for the complete cycle of crop production could be debated, but their potential for high-quality vegetable seedling production appears to be unlimited.        

This article was previously published in Practical Hydroponics.

 Organic hydroponics can seem like an oxymoron since many organic-food producers insist that soil is an essential component of the mix. However, as Dr. Mike Nichols explains, that’s just not the case… Soil provides a basic structure within which various organisms and microorganisms, roots, water, air and a wide range of organic and inorganic chemicals proliferate. However, there is nothing magical about soil; in fact, it isn’t always the best medium in which to grow high-value horticultural crops because it can be either poorly aerated due to ideal moisture conditions or too dry due to optimum aeration. The emphasis on soil as the basis of “organic greenhouse cropping” is false and there is no reason why organic nutrients cannot be used in a recirculating hydroponic system. Organics and soil Organic greenhouse horticulture is defined by the International Society of Horticultural Science (ISHS) as the production of organic horticultural crops—vegetables, ornamentals and fruits—using inputs derived only from natural, non-chemical sources in climate-controllable greenhouses and tunnels. There is no mention of soil-based systems in this definition. Much of the organic philosophy appears to be based on the UK Soil Association and the writings of Rudolph Steiner. Both organizations have their origins well before anyone considered growing crops commercially using hydroponic systems, so hydroponics did not get considered. But what is magical about soil? Soil is normally comprised of inorganic particles derived from rock (such as clay or silt or sand), organic matter (humus), a range of microorganisms, water, air and some nutrients dissolved in the water. In some “soils,” the inorganic particles may be partially or totally replaced by semi-decomposed organic matter (peat). Well, a recirculating organic hydroponic system can comprise all of the above, with the exception of the solid inorganic particles (although pedantically it would not be too difficult to add a few pieces of rock to the system to fulfill all of a normal soil’s characteristics). In fact, a recirculating organic hydroponic system is also much more sustainable than a soil-based system. One of the major claims of organic vegetable growers is environmentally friendliness, but from a sustainable viewpoint, a recirculation system is much better in nutrient and water efficiency. This is because considerable quantities of nutrients leach through the soil profile into the water table and aquifers in an intensive traditional greenhouse situation in order to obtain acceptable levels of production. This does not occur with organic hydroponic systems. Organic hydroponics In the early 1950s, virtually all greenhouse crops were grown in soil. The only exception was pot plants as for many years it was thought soil was not a suitable medium for these plants (potting compost was developed to sustain these plants). It was not until the ’60s that researchers began to consider alternatives to soil for the production of other greenhouse crops, such as tomatoes, cucumbers, and lettuce. What started as straw bales, peat base beds, etc. resulted inevitably in the establishment of commercial hydroponic systems like nutrient film technique (NFT) and rockwool. This had a huge influence on productivity and a marked increase in yield, as the complex balance of aeration and adequate moisture at the roots became much easier to obtain (the control of soil-borne pathogens also became easier due to isolation). Then, in 2001, a number of greenhouse studies were conducted at Massey University by Kim Atkin to compare conventional and organic hydroponic systems. He found that, in a comparison between an organically derived solution of liquid fish and liquid seaweed and a conventional hydroponics solution, lettuce raised using NFT grew faster in the conventional solution. This might have been due to the fact that some of the liquid fish solution was in suspension rather than dissolved, which might have caused anaerobic conditions. Nevertheless, the organically grown lettuce reached maturity only one week after the conventionally grown ones. Also, Atkin found that cattle effluent was capable of producing lettuce growth rates similar to those of conventional hydroponic solutions. Aquaponics Aquaponics can best be defined as a combination of aquaculture and hydroponics. In aquaponics, the fish and plants are produced in a single integrated system where fish waste provides a food source for the plants and the plants provide a natural filter for the water in which the fish live. A key factor is the bio-filter between the fish and the plants, which is comprised of bacteria that convert fish waste into soluble nutrients for the plant roots (a key conversion is ammonia—which is toxic to fish—into nitrite and nitrate). In studies recently undertaken in New Zealand that compare the productivity of lettuce and herbs within conventional hydroponics and aquaponics, the aquaponic system proved to be similar (or in some cases superior) to the conventional system. These results depended on the time of the year, as the productivity of herbs in the aquaponics system was reduced during the winter due to the poor feeding of the fish in the cooler conditions (see Tables 1, 2 and 3). In trials carried out in Italy, the productivity of aquaponic systems was not significantly different to that of a conventional hydroponic system. In the first experiment, a small quantity of fertilizer was added to the aquaponic treatment; but there was significantly lower yield. In the second experiment, however, no significant difference was found in the productivity of lettuce (when comparing aquaponics with hydroponics) thanks to the greater quantities of nutrients available in the aquaponics system during this second trial (see Table 4). Aquaponics is probably the ultimate in organic sustainability. In conclusion In North America and Scandinavia, there is a growing acceptance of the use of organic media (peat) and recirculating hydroponic systems that use organically derived nutrients to provide organically certified produce. (There would appear to me that the potential to use “untreated” coir might provide a valuable alternative if peat supplies ever became limited.) This makes sense. Soil is not a good medium in which to grow high value crops, because it is difficult if not impossible to provide it with optimum levels of both moisture and aeration. Also, producing high yields of greenhouse crops (a necessity in expensive capital structures) requires considerable inputs of nutrients. In a non-recirculation system, this poses considerable problems in terms of leaching into the water table. As such, the insistence on the use of soil rather than other media for organics and the objection to recirculating system is illogical in terms of sustainability. Also, to suggest that hydroponics is unnatural (as has been suggested by some) is to limit our future to being “hunter gatherers” rather than farmers. In my view, the key factor for the future must be sustainability and soil-based organic greenhouse systems are not sustainable in practice, whereas organic hydroponic systems are far more sustainable. Literature Cited Atkin, K., & Nichols, M. A. (2004). Organic hydroponics. Acta Horticulturae, 648, 121-128. Cooper, A. (1967). The ABC of NFT. London: Grower Books. Ho, L.C. (2004). The contribution of plant physiology in glasshouse soilless culture. Acta Horticulturae, 648, 19-26. Nichols, M. A., & Lennard W. (2010). Aquaponics in New Zealand. Practical Hydroponics and Greenhouses, 115, 46-51. Pantanella, E., Cardarelli, M., Colla, G., Rea, E., & Marcucci, A. (2010). Aquaponics vs hydroponics: Production and quality of lettuce crop. 28th IHC Abstracts I, 35.

 Globally loved ginger is normally grown in tropical/sub-tropical soil. Author Mike Nichols, however, has decided to try growing this rhizome with hydroponics…

Ginger (Zingiber officinale) is a swollen root—or, rhizome—that is consumed as a food, a spice or flavoring, and a medicine against nausea. There are over 1.5 million tonnes of ginger produced in the world, but as a tropical/sub-tropical crop the main production areas are found in India and PR China (aprox 350,00 t each), followed by Indonesia, Nepal, Nigeria and Thailand (about 150,000t each). There is even a small area of ginger produced in Australia that supplies the local market and is exported worldwide.

The plant itself comprises several upright, grass-like leaves that grow from the rhizome, which has both fiberous and thick roots. The plant steadily expands with the production of new rhizomes (the roots come first and produce the stalks from which leaves grow). The characteristic odor and flavor of ginger comes from fragrant essential oils, particularly gingerols, found within the rhizome.

The success or failure of ginger production is determined by the health of the “seed pieces” (pieces of the rhizome) and the health of the soil. Diseases, particulary fusarium and pithium, and pests like nematodes can seriously reduce production. All growers anticipate some losses every season due to disease. However most growers believe that a 10% losses in a patch are acceptable and, at times, some patches can experience over 80% losses. In Hawaii the soil pathogen problem is so serious that it is normal to fumigate the soil with methyl bromide. The Queensland bulletin on ginger production also cites crop establishment in Australia being anything from as low as 5% to up to 95% due to soil borne pathogens.That being said, it’s no surprise that disease-free planting material is highly desirable.

While at a hydroponics conference in Adelaide last year I was asked about growing ginger using hydroponics. I confessed complete ignorance, but this stimulated my interest to investigate the potential of using this production system—which is becoming well-established for many crops—for the less common goal of growing a root crop.

The first approach was to review the existing literature on the subject. I, however, only discovered three papers on the hydroponic production of ginger—namely Kratky (1998), Rafie et al (2003) and Hayden at al (2004)—and numerous articles on the world wide web that were how-tos without any research findings.

The Kratky paper proposes that the production of ginger using a non-circulating hydroponic method, in which essentially the plants were grown in plastic nursery flats filled with a growing medium comprised of peat, vermiculite and perlite. The plastic nursery flats were suspended eventually some 4 cm above a static nutrient solution once the roots had moved throught the medium into the solution. The Hayden paper was similar to some respects, except that instead of a static nutrient solution the growing medium was suspended above a tank in which the roots grew, and the nutrient solution was applied as a fine mist using aeroponics. The third (and simplest) system, explained in Rafie et al, used trays filled with  a medium of coarse perlite. Plant spacing was 1.5 ft x 1 ft (1.35 x 0.3 m).

All systems appeared to work satisfactorily. The Hayden trial showed major disease problems when using peat as a growing medium, illustrated the importance of a growing medium (perlite in this case) for the rhizomes (as opposed to no growing medium), and demonstrated that heating the nutrient solution to 25ºC produced rhizomes that were 50 per cent larger. The Kratky paper also showed low yields without the use of a medium over the rhizome and that the more medium volume the better. The Florida paper merely shows that the hydroponic system produced nearly double the yield of a field soil system.

In our experiements, since ginger is not grown in New Zealand and introducing it via quarantine can be a tedious (and expensive) exercise, we purchased imported dried ginger roots (rhizomes) from  a local supermarket from Fiji (or Australia) and from Thailand. It was unclear whether this might have been treated to prevent sprouting, but in fact it sprouted easily when planted in a moist growing medium in a greenhouse.

We started the rhizome pieces in small pots filled with coir in September (Fiji source) and November (Thailand source), and once they had produced a shoot and some roots they were transferred into large pots filled with coir (cocopeat) and with a single dripper nozzle to each plant. A complete nutrient solution was applied with every watering, and the plants were grown in a greenhosue heated at 15ºC and ventilated at 25ºC.

In early May it was decided to examine the plants to determine whether any ginger had developed, and we were gratified to discover that the sytem had worked succesfully. As one might anticipate, the early planting had produced the greater yield and there clearly could be some advantage in planting even earlier than September so that the plants would be much larger in mid-summer when growth potential is greatest.

Is this the way to grow ginger hydroponically? The answer (in my view) is a clear cut no.  The more sensible solution would be not to use pots, but to grow the crop in beds filled with a good, well-drained growing medium (coir certainly fits this bill) using hydroponics. The key factor would be to isolate the beds from the soil, either by using beds on benches or a layer of polythene film over the greenhouse floor. The importance of temperature is clear from the Arizona research, and this must pose the question of whether greenhouse production might even be an even better option in warm climates such as India or Australia?

Of course, the longer the plant is grown the higher the yield, but apparently the rhizomes also become more fibrous; so for candied ginger, the younger rhizomes are likely to be more desirable. If the crop is being grown for the oils alone, such as for flavouring ginger beer, then the oil content (and differences in chemical constitution) is likely to be influenced by genotype, possibly by harvest date, and by the way in which the crop has been grown.

This article was originally published in Practical Hydroponic.

Do not publish the following in the print version. But, do publish it online.

References

Hayden A L, Brigham L A &  Giacomelli G A  (2004).   “Aeroponic Cultivation of Ginger  (Zingiber officinale) Rhizomes” Acta Hort. 659, 387- 402.

Kratky, B A.  (1998).  “Experimental non-circulating hydroponic methods for growing edible ginger”. Proceedings, 27th National Ag Plastics Congress. Tucson, Arizona, USA.  Feb18-21, 1998. pp 133-137.

Rafie R A , Olcyk T, & Guerrero W (2003).  “Hydroponic production of fresh ginger roots (Zingiber officinale) as an alternative method for South Florida.” Proc.Fla State Hort. Soc. 116, 151-2.