The problem could be avoided if hydroponic production proved to be a viable alternative to growing in soil.
In project PO 020 a, "deep-pool" trial facility was constructed at JA Collison & Sons. Stocks, statice, lisianthus and, as a comparison, lettuce were grown on rafts floating on water 25-30cm deep. A small secondary trial was undertaken a little later in other pools where the water was only 10cm deep.
The nutrient solution was constantly circulated through the system, oxygenated via a venturi, and its nutrient status monitored.
Unlike the stocks, both the lettuce and lisianthus plants grew away vigorously. Vegetable brassicas were subsequently tested in the deep pool to see whether the issue was with cruciferous plants - they thrived, but the stocks continued to die.
At 20 per cent, the oxygen levels in the water were found to be too low for stocks. Levels were boosted by introducing air stones into the pool and growth of plants adjacent to them improved. However, the effect was localised, with stocks further away growing no better than before, even though oxygen levels had increased three-fold.
Some plants also succumbed to Phytophthora. Subdue (metalaxyl-M) was introduced to the solution, after which few additional plants became infected.
One of the shallow pools in the secondary trial used an experimental form of electrolysed water, releasing free available chlorine into the solution. This produced some of the best flower stems of the season, although they did not open until late October.
You can read more about PO 020 on the AHDB Horticulture website.
For details on all AHDB Horticulture activity, see horticulture.ahdb.org.uk