29th Aug 2007
strong>Heaviest Onion 29th August 2007
My attempt to beat the world record for the heaviest onion came to a grinding halt a few weeks ago. This was only my second attempt at growing a really heavy onion with the first attempt many years ago in my onion bed at home. I was given a few plants by Robert Holland from Scotland who at the time was holding the World record. I can’t remember what weight it was but it came in eleventh position at the Harrogate weigh in which wasn’t too bad at all.
This year my second attempt was through using the hydroponics system when plants are grown with their roots in water and added nutrients. The system I used was from Aquaculture in Sheffield after first seeing it demonstrated at my Gardening Weekend last November by the owner Simon Spinks. It’s relatively easy to use comprising of two shallow tanks, one sitting on top of the other. The bottom tank has a small electric pump and around 40 litres of water with added nutrients, these have already been made up in a separate container to be added to the 40 litres of water.
The upper tank is full of small brown clay balls into which the onions are planted directly having first been grown into strong plants in rock wool squares. The idea is that the pump comes on three times a day for four minutes to pump the nutrients from the bottom tank to the top one and then drain back out again. The roots of the onion will cling on to the clay balls where they can take in the nutrients as required.
There are really only two elements to control in the whole growing regime, the PH and the Conductivity level. Both have to be kept at a certain level if the plants are to grow to their optimum. The PH has to be kept above 5 and below 7 with the ideal being around 5.5 to 6. The Conductivity is the one element that controls the amount of nutrients that the onion takes in. Initially It was kept between 12 and 13 and the onions grew away well.
It was apparent during early August that the biggest onion was struggling after it reached 24 inches around as the tips of the leaves were yellowing and it was very reluctant to send up a new young leaf. The leaf that was sent up eventually was wrinkled and certainly didn’t look very happy. It has now finished growing at 25.5 inches in circumference and I shall remove it from the tank this coming weekend.
A second onion that was always an inch and a half behind the other seemed to be growing better, regularly producing central leaves. However that has also now hit a brick wall and will also stop at around the same measurement. One thing that I need to do for next year is to discuss with Simon Spinks why the onions are coming to a halt at around this size. It’s not just me either, Gerald Treweeks' onions also stopped at about the same size.
I have a feeling that we were pushing the Conductivity levels too high with the cell walls within each onion already with sufficient nutrients within them. My feeling is that we need to run the Conductivity levels much lower, possibly at 10. The big question is, do I run the system at 10 throughout or start off with a higher reading then dropping down to a lower one at some point. The big question that we have to get right is, at what point and to what level do I drop the conductivity reading. I have enjoyed immensely growing the onions and I’m sure it’s possible to grow some very large quality onions using this system - watch this space for next year.