How do I grow hydroponic mint?

I have read the article on mint in your Issue 132. I am also trying to grow mint in hydroponics in India. Would you please guide me in a few things:

  • What is water pH and TDS levels? 
  • What is the temperature to be maintained in the greenhouse?
  • What is the pest control method used? 
  • What nutrients are used?

Answer by RICK DONNAN


If you are planning to grow mint on a commercial scale, then the most important aspect for you is to get to know the crop and how to grow it from the horticultural aspect, not merely the hydroponic aspect, which is often overstated.

I’ll comment on your hydroponic questions, but then give an overview of the skills needed to be successful.

TDS (total dissolved solids) is not a good measure for solution strength in hydroponics. This is because a TDS meter is actually an EC (electrical conductivity) meter with an inbuilt conversion factor. Problems arise because different meters have different conversion factors, so stick with an EC meter measuring in milliSiemens/cm (mS/cm).

There are no special levels of pH or TDS or nutrient formulations reported for mint, so use typical values until you can do your own trials.

A reasonable pH range in the root zone solution would be 5.5 to 6.5, and the EC 1.5 to 2.0 mS/cm. Both should be able to go wider without problems. For fertiliser, any standard vegetative mix should be OK. Points to watch are that you use an actual hydroponic fertiliser, not a so called ‘complete’ fertiliser which is intended for soil growing and is totally unsuitable for hydroponics. Also check that the iron in the fertiliser is in a chelated form.

Horticultural skills
Particularly, new and intending growers need to take care to not be blinded by ‘hydroponic technology’. While the technology is important, having a good working knowledge of horticultural art and science is hugely more important.

In my opinion, the ‘80/20 Rule’ applies here. Of the growing skills required to grow a good commercial intensive horticultural crop, about 80% relate to horticultural skills and only about 20% to hydroponic skills. Put another way: if you grow mint, you are a mint grower using a hydroponic technique, rather than a hydroponic grower growing mint.

In general, the best we can aim for is to provide ideal conditions in the root zone for the plant to perform as well as possible. Remember that the hydroponic system only works through the root zone, and the aerial portion of the plant has the major influence on the plant’s performance.

The major foods of the plant are carbon dioxide (CO2) and water (H2O). When acted on by sunlight the plant leaves combine these (through the process of photosynthesis) to produce sugars and emit oxygen (O2). These sugars are the bulk food of the plant. The nutrients you add are only a part of the plant’s food needs and could be considered as equivalent to the vitamins and minerals we need.

Environmental control
Controlling the environment effectively is the single most important aspect of achieving maximum production of a particular crop. Growers need to make the best use of the equipment they have. This means acquiring a good knowledge of the settings to get optimum results and continuously checking the actual conditions achieved.

Pests and diseases
Ideal growing conditions in a greenhouse usually mean they will also be ideal for some pests. Identifying pests as early as possible and knowing how to sensibly control them, preferably using IPM, is a critical horticultural skill.

While a well managed hydroponic system can usually avoid soil borne root diseases (often a major reason to go hydroponic – to get out of disease prone soil) this is not always so. Also, a properly controlled environment can greatly reduce the risk of developing some diseases, especially mildews. However, diseases can still be a major problem, and can be spread by insects and workers. Again, a grower must acquire the skill to recognise disease risks and use preventative measures, including good hygiene practices, to reduce the risk.

Crop culture
By this is meant the management of the plant. This may include aspects such as: propagating technique, time of planting, plant density, crop support, training plants (such as up strings), initiating flowering, pollinating, pruning, disbudding, deleafing, truss pruning, balancing leaf area and fruit load, manipulating vegetative and generative influences, stage of flower/fruit development for harvest, timing when to stop the plants, etc, etc.

Quality control
While not every grower is quality assured, this is becoming an ever increasing requirement. However, every good grower should have an interest in using quality control techniques to ensure the best results are achieved and problems can be traced.

Other skills
This answer concentrates upon growing skills, however, as for any small business there is a need for many other skills if your business is to be successful. The full range of management skills is needed: planning, financial, staff, repairs and maintenance, etc.

Once everything else is in place, ultimate and ongoing success will eventually depend upon successful marketing. That is, can you sell your produce for a price that gives you a reasonable return? Ω

PH&G January 2016 / Issue 163


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