Reader Inquiries

Answers by Rick Donnan

What do we need to do to eliminate the need to water leach?

I read the response to the inquiry, ‘Should I flush my growing medium?’ in your magazine. My question is, “what do we need to do to eliminate the need to water leach”, which means matching the nutrient solution formulation and its use factors based on the water-holding capacity of the rooting medium, which no one is investigating. So, we slosh on the nutrient solution and then monitor the EC of the retained solution, and at some point water leach to remove the accumulated ion, known as ‘salts’. What a waste! See More

Should I flush my growing medium?

I use cocopeat as a medium to grow tomatoes, feeding them with a hydroponic fertiliser through a dripper per plant. I flush regularly with water to prevent salt build up, but was recently told that you recommend flushing with nutrient solution. Is this right? If so, please explain why. Answer by RICK DONNAN See More

What can I do to reduce acid addition?

I have a hobby hydroponic system using cocopeat in bags, fed by drippers. I have found that the pH of the solution running from the bags is much higher than what I am feeding. I have to add ‘pH down’ to bring my feed down to 5.0 pH in order to keep the run-off pH under 6.3. This is using a lot of pH down. I guess that the pH down I use is an acid, but I don’t know what kind. Is the amount of acid I am using doing any damage to my plants, and is there anything I can do to reduce the amount of expensive pH down I use? Answer by RICK DONNAN See More

Is algae a problem in hydroponic systems?

Should I be concerned about algae in my hydroponic growing system?

Answer by RICK DONNAN See More

Planning a commercial hydroponic enterprise

From a newcomer to the industry, querying how to plan a commercial hydroponic enterprise.

I want to do hydroponics at a commercial level, but it is difficult for me to plan every thing like: capital cost, labour cost and electricity cost. Can you please guide me? Answer by RICK DONNAN. See More

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? See More

What are the fundamentals of setting up an NFT system?

What factors are important in setting up an efficient NFT system for different types of plants?
See More

Organic acid for pH adjustment?

I am growing organic strawberries on table-tops in peat moss.  My system is therefore very similar to hydroponics. I have found that my water pH is quite a bit too high, and I wonder if you could recommend the best options for organic pH adjustment?  My operation is small-scale commercial, so cost is a definite consideration. See More

What is the difference in results between soil and hydroponics?

Rick Donnan

Rick Donnan

I have noticed many different claims of the advantages of hydroponics over soil growing, especially a wide variation in figures for relative yields and water use. Are there any standard and reputable data available? See More

Is osmosis the mechanism for water uptake?

Rick Donnan

Rick Donnan

I believe that osmosis is the mechanism for the uptake of water by plants in hydroponics. Is this correct and how does it work? 


Yes, osmosis is the mechanism for water uptake by plant roots, but this applies to all plants, not just those growing in hydroponics. Where hydroponics has an advantage is that the grower has some control over the root zone solution strength (usually measured by EC—electrical conductivity). It is the root zone solution strength which has a major influence upon osmosis and hence water uptake. See More