Reader Inquiries

Answers by Rick Donnan

What are good management practices for media-based systems?

Thanks for your answer highlighting the importance of measuring the run-off solution from media-based systems (Reader Inquiries April 2017) and your detailed description of how to do this. Are there other management issues for media-based systems that hydroponic growers need to be aware of?

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How do you collect a sample of the root zone solution?

In my answers I frequently refer to the root zone solution. That is, the solution around the plant roots from which the plant takes up water and nutrients, as explained in my previous two columns. I stress that it is this root zone solution, which is the basis for good hydroponic management. Many growers obsess about their feed solution, but this is only a means to managing the root zone. I am often asked how to collect a root zone solution sample from a dripper-fed container of medium, so this is my practical answer to that question.

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How do plants take up nutrients?

From an indian grower:

Please refer your answer to the reader’s question in the February 2017 PH&G issue.

You have mentioned that in osmosis only water moves from lower concentration to higher concentration and salts do not get through the membrane. If this is so, then how do nutrients reach plants? I am a grower and a regular reader of your magazine. Thanks a lot. See More

Why are my tomatoes and capsicum turning black?

I have a small greenhouse in which I grow 12 tomato and six capsicum (sweet pepper) plants. They are growing in bags of dripper fed coco peat. I use a standard “bloom” liquid fertiliser at the recommended strength (4 ml each of A and B per litre water). The older fruit of both the tomato and capsicum have turned black on the bottom. The tomato plants generally look OK, but the capsicum plants are looking poorly.

Can you suggest what is wrong and what I can do to fix the problem?

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How do I visually assess nutrient deficiency symptoms?

I am a hobby hydroponic tomato grower. My plants are producing well, but recently I noticed what appears to be a nutrient deficiency. The youngest leaves are turning yellow between the veins. Can you suggest what it is?

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Should I use nutrient solution analysis or plant tissue analysis?

I am a commercial tomato grower, experienced in soil growing, but have now gone into hydroponics, using bags of coco peat. I am used to having tissue analysis done, but I have been told that I would be better off getting nutrient solution analysis. What do you suggest?

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Can ‘bloom’ fertilisers force plants to flower?

I am a hobby grower new to hydroponics. I notice that some hydroponic fertilisers are labelled as ‘bloom”. I am getting conflicting comments as to whether these can force plants to flower. Is this possible?

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Should I use twin skins if building a polythene greenhouse?

I am considering building a single span poly house to grow speciality cucumbers. I have a friend who says twin skins are essential if I plan to heat the greenhouse, but others warn that the twin skin loses light. What do you recommend?

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How do I convert a formula in ppm to amounts of individual fertilisers?

I have received several successfully proved formulas for the crops I grow, however they are expressed as ppm (parts per million) of the various nutrient ions. How to do convert these to the practical amounts of fertiliser to use?

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Water quality needed for different hydroponic crops? – Part 2

Following on from last month’s question on water quality, here are some more guidelines. These list the Dutch guidelines for the maximum levels of sodium that are acceptable in recirculating solutions for a range of crops.

I have also included more recommendations as to different water sources, especially the collection of rainwater.

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