Reader Inquiries

Answers by Rick Donnan

What do I get from attending a conference?

Comment by Rick Donnan. What do I get from attending a conference?

I have been involved with organising hydroponic conferences since chairing the organising committee of the first Australia Hydroponic Association (AHA) Conference in 1990. I have had an involvement with all 10 subsequent biennial conferences. The AHA is now Protected Cropping Australia. I am often asked by growers why they should come to conferences and how can they justify the expense? See More

Does your previous answer also apply to growing in the soil?


From a Victorian hobby grower. Does your previous answer also apply to growing in the soil? 

I am a ‘back yard’ grower in Victoria and a volunteer in a larger scale ‘farm-like’ vegetation area. We grow vegetables the ‘traditional’ way in soil – not hydroponic. I am reading the hydroponic magazine out of interest – with an idea of becoming a hydroponic grower in the future (depending on the capital
investment needed).

I read your interesting answer about ‘fruiting tomato plants’ where you had mentioned the ‘number of leaves per stem’ etc. My question is a general one: is this formula true for in soil plants as well? Are there similar formulas for capsicum, eggplant, pumpkin plants? That is, should we cut off leaves and change the feed in order to increase the number of fruits and their size? See More

Why are my tomato plants not fruiting?


From a NSW hobby grower. Why are my tomato plants not fruiting? 

My tomato plants look healthy, but the flowers are not forming any fruit. There are plenty of flowers and the first two or three trusses produce fruit, but there is no fruit forming on the later trusses.

I grow the plants on reused coco slabs using a recycling drip irrigation system, feeding in an EC of 2.8 mS/cm. I use a general purpose two-part ‘Grow’ nutrient available from my local hydroponic store. I grow outdoors in a protected sunny spot and run the plants up a single string. There is no evidence of pests or diseases. Plant stems are thick and the leaves are dense and dark green in colour.

What is my problem? See More

Why is my hobby hydroponic system giving problems?

From a nursery propagator. Why is my hobby hydroponic system giving problems (edited)?
I have a small specialised propagation nursery propagating difficult to strike shrubs. Once I have struck the cuttings I transplant them into large tubes containing an open potting mix, which includes a small amount of wide range slow release fertiliser. I normally lightly water several times per day and occasionally give a feed using a complete soluble fertiliser.
I have had an interest in hydroponics for some time so I decided to set up a hobby system. What I bought was a small NFT (nutrient film technique) system with a table holding five 100mm wide x 50mm high channels 6 metres long. I grow mainly lettuce and herbs, but some other vegetables as well.It has a tank underneath with a water make-up float valve. On most days I check the EC and pH and make the EC back up to about 1.5mS/cm using my nursery fertiliser. I find that the pH is always low so I add ‘pH up’ to bring it back to about 6.3.

My problem is that the plants don’t look healthy and are weak. Do you have any suggestions as to my problem and its solution? See More

How do pesticides work?

From an anonymous grower. How do pesticides work?
I recently had a can containing some two-stroke petrol, which had gone off. Having seen where spilt petrol/oil has killed grass, I decided to use it as a weed killer using a rough hand sprayer. Later on that same hot day I sprayed another weed patch with ‘Roundup’ herbicide at the recommended strength, using the same hand sprayer. It is now a week later and I can see the results.

 Those weeds sprayed with the herbicide are wilting, and the entire plant has turned yellow. Different types of weeds are coloured to different degrees, but all are obviously dying. 

The weeds sprayed with the petrol are different. There are strong yellow spots on the leaves, obviously where the actual petrol droplets have hit. The remainder of the leaf is still green.

Can you explain this difference? See More

How do I manage acid addition and pH rise?

From a NSW hydroponic tomato grower.
How do I manage acid addition and pH rise?

I grow tomatoes in greenhouses south of Sydney. I use phosphoric acid to lower my pH. I have been adding increasing amounts of acid to bring my feed pH down about 6.0, but it is still rising to about 7.0 in the run-off. I have been adding some liquid ammonium nitrate to reduce the pH rise, but it has only reduced the pH rise by about 0.2 pH. I have had some symptoms of what has been suggested is iron deficiency. That is, the young leaves are pale and the veins show up darker on the pale leaf.

An analysis was done of my feed and the laboratory advised that it was generally OK, except that the phosphorus (P) level was high. I would like to add more acid, but that will make the P level even worse.

Can you suggest what I should do? See More

Should I use hydroponics to grow stock plants?

From a New South Wales Nurseryman.

Should I use hydroponics to grow stock plants? 
I have a nursery in which I specialise in propagating large numbers of a narrow range of native trees from cuttings. I know there are a few nurserymen who grow their stock plants in hydroponics. Would you suggest that this is a good idea? If yes, could you give me some guidance on the fundamentals. See More