As this years trial is now coming to an end, this post is an update on recent progress. As reported previously, the addition of large amounts of oxygen to the water by the use of individual air stones had shown a remarkable effect on the growth of the column stocks. Unfortunately this did not prove to be the whole story and a couple of weeks later these strong, healthy looking plants started to wilt and looked distinctly unhealthy (just in time for the open day)! The problem appeared to be at the stem base rather than the roots and this resulted in the root and stem detaching themselves from each other (see left hand photo).
These were send to the lab and Phytophthora was identified. It was recommended that we added Subdue (metalaxyl) to the tank to see if this would eliminate the problem. Unfortunately because of it being the end of the stock season it was not possible to obtain any new plugs to plant before adding the Subdue hence we could only look at its effect on these already planted (although some had only been planted for a couple of weeks).
Now that most of the stems are flowering it would appear as if the effect of the Subdue has been quite significant with very few additional plants succumbing to Phytophthora (although those already wilting did of course not recover). The following photos show the flowering stems on the 22nd of September and as can be seen, while these are by no means perfect (and not supported hence some have fallen over) they are probably as good as you can expect for the end of September
However one very interesting result is that since the addition of Subdue, the positive effect of the air stones can be seen much wider than the immediate float above them. This is something that needs to explored further and also to see if it can be repeated if the tank is replanted next year.
The chrysanthemums, asters and statice continue to romp away and in a commercial situation these would obviously need some form or support to hold them up. The chrysanthemums have now started to bud up (see right hand photo).
A decision now has to made about the continuation of this trial into next year and we would welcome your views on this.