Is there a culture of denial with hydroponic produce?

On hydroponics generally, is there a culture of denial by retailers? If so, what is the reason?

My wife and I were in the vegetable section of our local supermarket recently and asked someone who bore the title of Assistant Manager whether the lettuce and tomatoes we were buying were hydroponic. He said he didn’t know but shouted across to one of the shelf stackers whether he knew. “Hydro what?” was the reply.

Surely, retailers must know what they are selling? We even phoned the customer service department of the lettuce grower and no one knew there either!

Is there a deliberate culture of silence on the subject and if so for what reason? Are vegetables grown in soil presumed to be ‘good’ and those grown hydroponically ‘bad’?

The lettuce we bought was we presume hydroponic.The roots were quite long and still attached. What we are curious about is what appear to be a scattering of ‘metallic’ pieces embedded in the roots. This is presumably fertiliser. Do you know what it is?

‘Metallic’ pieces?
Yes, lettuce with their roots still on would certainly be hydroponic living lettuce. Obviously, these cannot be grown in the soil.

Firstly, what are the ‘metallic’ pieces?  They would be small pieces of vermiculite, which typically has a shiny appearance, but feels relatively soft rather than a hard metallic feel. Vermiculite is an inorganic potting mix component, which holds a high water content. It is typically used in seed raising mixes or as a coating to keep the seed wet in order to improve germination. Similar mixes are used whether propagating to grow in hydroponics or in the soil.

Hydroponic history
The history of the introduction of hydroponic produce is interesting as it provides a background to your inquiry.

The first large scale use of hydroponics was in Japan, immediately after the war. The local produce was grown in the soil, mainly fertilised by ‘night soil’; that is, human excreta. The army command justifiably feared that the occupying troops would be vulnerable to picking up diseases to which the local population was largely immune. Consequently, the US Army installed a 55-acre hydroponic farm, which used gravel beds. This farm continued to operate for 10 years, providing fresh vegetables to the occupying forces and also to UN troops during the Korean War.

The first significant use of hydroponics for commercial growing started in Canada. In the mid-1960s, there was a substantial glasshouse industry in British Columbia, supplying tomatoes into Canada and the USA. Growers had increasing problems with the soil disease fusarium. Eventually, this reached the critical point where the choice became to either give up growing tomatoes or get out of the soil. They successfully moved into growing hydroponically in sawdust in bags.

Interestingly, the first significant commercial use of hydroponics in Australia was also due to a strain of fusarium. Carnation growers were moving under cover to improve flower quality and were sterilising the soil. However, when the roots of the long-term carnation crop spread beyond the sterile zone, the crop would collapse. In the open, they could plant in another field, but in a greenhouse the only choice became to get out of the soil. Growers moved into dripper fed bags or boxes containing potting mix, scoria or rockwool.

The Netherlands
The Netherlands has long been the world leader in glasshouse technology. Local environmental issues resulted in it also leading the way in the adoption of hydroponic growing techniques. By 1980, excessive levels of methyl bromide were detected in the canals in the glasshouse areas; consequently, it was banned as a soil sterilant. Other sterilisation techniques proved ineffective for some crops, forcing them out of the soil into hydroponics, typically rockwool slabs and later cocopeat.

High levels of nutrient in the canals from soil and hydroponic run-off resulted in all glasshouse growing systems having to be closed (recirculated) by 2000. Since then, all 10,000ha of Dutch glasshouses (approximately half vegetables, half flowers) use closed hydroponic systems and much of the Western world also.

Australian leafy greens
Australia has a small unique place in international hydroponic production. Starting in the mid-1980s, we developed NFT (nutrient film technique) channel systems on working height tables to produce living lettuce. (I described these in detail in my column in the previous issue—October 2014). We now have a greater NFT area than the rest of the world combined.

These systems are excellent for growing short term leafy green crops. Most of these systems are outdoors, but increasing areas are going under cover. All living lettuce is grown this way—mostly the fancy-type lettuce varieties. If the roots are placed in water, the lettuce stays much fresher than if it is cut. A high proportion of fresh herbs are grown hydroponically, some as living herbs but most as fresh cut. Increasing numbers of Asian greens are being grown this way—as with lettuce, it has the major benefit of eliminating soil contamination.

With both fresh cut herbs and Asian greens, there is no differentiation between whether they are grown in the soil or in hydroponics. The difference only shows sometimes in that the hydroponic produce is often of better quality. The cost of producing hydroponically is usually higher than soil growing, but is typically offset by higher and especially more consistent production and quality.

Other Australian hydroponic produce
Virtually all the greenhouse cut flowers you can buy here, whether locally grown or imported, other than wild flowers, are grown hydroponically.

The proportion of fresh tomatoes grown in greenhouses is steadily increasing with a corresponding reduction in field crops. Processing tomatoes used to be grown locally in the field. They have not been replaced by hydroponic tomatoes, but by imports. (My supermarkets used to have large numbers of tinned Australian tomatoes, now I often can’t find them.) Truss tomatoes and specialties such as cocktail tomatoes are grown hydroponically. Loose tomatoes can be grown in the field, under cover, hydroponically or in the soil, or any combination of these and not differentiated—they are tomatoes.

Lebanese and continental (long) cucumbers are all grown in greenhouses, mostly hydroponic but some still in the soil.

Other greenhouse crops mainly grown in the soil but now increasingly hydroponic are capsicum and eggplant, at the top end of the market.

The next big change coming is the large-scale hydroponic production of a range of berry fruits.

Hydroponic food production became significant during the 1980s and has continued to expand rapidly worldwide since then. The millions of tonnes of hydroponic produce grown around the world annually are sold as quality or greenhouse produce and rarely as hydroponic. Why is this? I don’t know, but I’ll have two guesses:

•   The primary aim of growers producing a quality product is to have that quality recognised. To promote hydroponics requires an expensive education campaign and introduces confusion. Better to spend that money advertising good quality.
•   For most people their exposure to the name hydroponics is through media stories about illegal cannabis growing—not a good look.

Initially, hydroponic lettuce was often marketed as hydroponic or ‘hydro’, but this is now less common. Presumably customers are looking for quality living fancy lettuce and aren’t interested in how it is grown. The quality of the end product is what is important.

Culture of denial?
The reason for poor staff knowledge is basically ignorance, rather than a ‘culture of denial’. Whether produce is hydroponic is well down the list of knowledge priorities, compared to for example country of origin. Whether hydroponic or soil grown often can’t be determined, because produce can be mixed right from the pack house.

Your question implies that there is something ‘bad’ about hydroponic produce. This is wrong.

Sometimes people assume that all the ‘goodness’ in vegetables comes into the plant from the soil via the roots. This is incorrect. The major ‘food’ of plants is light, normally sunlight. The process of photosynthesis uses the energy from the sunlight to produce sugars and oxygen. In the allied process of respiration, the sugars are converted into the myriad of compounds distributed around the plant to help it grow and produce flowers and fruit.

The roots take up water and mineral ions. In soil growing, the minerals come from the soil and added fertilisers. In hydroponics, the mineral ions are all in the nutrient solution. The form of the mineral ions is the same regardless of their source. For example, plant roots take up nitrate ions. Nitrate ions are identical regardless of whether they started as chicken manure, attached to soil particles after a thunderstorm, or industrially produced from nitrogen in the air to make an inorganic nitrate fertiliser. In hydroponics, water and mineral ions are usually more readily available for uptake by the plant roots than in the soil and hence, the effective root volume is much smaller than in the soil.

In general, open field growing can sometimes give excellent produce, but at other times have major difficulties. A combination of greenhouse growing with hydroponics significantly reduces the variability. Growers will always have different levels of skills, but a good greenhouse hydroponic grower should be able to grow quality produce year round.

Note that major supermarkets require their produce suppliers to have a substantial food safety quality assurance scheme. A compulsory part of these schemes is that they require regular audits for which the grower pays thousands of dollars per audit.

Modern glasshouse production
Modern glasshouse and hydroponic technology brings many benefits to the environment and the consumer. For example, let’s consider tomatoes, the major hydroponic crop.

In the open field and unheated greenhouses, problems often arise when the air gets cold and the relative humidity very high. These conditions lead to infection with powdery mildew and botrytis (grey mould), which have to be controlled with sprays. Growers will allow for the legal withholding period after spraying before harvesting, but in a modern glasshouse these conditions never arise and powdery mildew and botrytis are virtually things of the past and these sprays are not needed.

Gas is used for heating, usually during the night. Burning the gas produces CO2, which can be used to increase production during photosynthesis, however, this can only happen through the day. What is now done is to burn gas to produce CO2 through the day for use by the crop. The heat produced heats water for storage in a large insulated tank, and the hot water is used to heat the glasshouse when needed during the night. This gives a substantial reduction in CO2 emissions into the environment.

Glasshouse growers are well advanced in the use of Integrated Pest Management (IPM), which significantly reduces the use and severity of chemical sprays. There are an increasing number of types of beneficial insects now available in Australia so that many growers are now virtually using only biological control of pests and diseases. One aspect of this is to install fine screens over glasshouse openings to exclude major pests.   Ω

Rick Donnan

PH& November 2014 / Issue 149