Reader Inquiries

Answers by Rick Donnan

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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Water quality needed for different hydroponic crops?

I am considering setting up a small commercial hydroponic farm using a recirculating system. I have read that water quality is very important for hydroponics, especially when recirculating. Is this correct and can you give me some guidelines as to the quality required to grow different crops in hydroponics?

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Should I use a PAR meter for greenhouse climate control?

My greenhouse climate and irrigation controllers are years old and use a lux sensor for light measurement. I was recently told that I should be using a PAR (Photosynthetically Active Radiation) meter. This is apparently much better than a lux meter. Is this correct?

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Can we use chlorine dioxide to prevent diseases?

Can we use stabilised chlorine dioxide continuously in the irrigation system to prevent diseases and biofilm (on a system that recirculates drain water)?

Can we spray chlorine dioxide directly on crop leaves, to prevent diseases in general, specially fungal diseases?

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What is IPM (Integrated Pest Management)?

I have been reading about IPM and am somewhat confused as to whether it is biological pest control. If so, it must be difficult to buy and manage the beneficial insects before the pests get overwhelming. Is there a different explanation?

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Do you need to whitewash a greenhouse with UV protective glass?

Your question implies that the main function of applying whitewash to a greenhouse cover is to prevent the transmission of UV (ultra violet) light into the greenhouse. This is not correct. The main function of whitewash is to reduce the heat load upon the crop in the greenhouse by reflecting a significant proportion of the incoming Infra Red (heat) portion of solar radiation. This is aimed at periods of high solar radiation, that is, around summer. See More