Reader Inquiries

Answers by Rick Donnan

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?

Answer by RICK DONNAN See More

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?

Answer by RICK DONNAN See More

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?

Answer by RICK DONNAN See More

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?

Answer by RICK DONNAN See More

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?

Answer by RICK DONNAN See More

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?

Answer by RICK DONNAN See More

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.

Answer by RICK DONNAN See More

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?

Answer by RICK DONNAN See More

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?

Answer by RICK DONNAN See More

Translator