As part of our ongoing quest for a long-term stored peony of good quality, here are the results of our ULO-storage experiments, year 5 already.
For those readers that are only now learning about these long term Utra Low Oxygen (ULO) treatments: we use large plastic boxes which can be closed airtight. Those boxes have several membranes that can be closed so as to let more or less fresh oxygen in. As the peonies inside use the oxygen to breathe, inside the box the oxygen proportion of the air steadily decreases from about 21% to some 5% (the ULO condition) at which point the peonies slow down their breathing rate and hence their ‘ageing’. It is a treatment which is commonly used for hard fruits like apples and pears to store them longtime and have produce available outside of the harvesting season. Unfortunately the procedure with peonies is not as straightforward as with those fruits and previous years have mostly resulted in disappointments as for example last year.
This year was a terrible year when we look at peony diseases. A very late deep frost in Spring and then rain and drizzle for weeks upon weeks resulted in a very high proportion of botrytis infected stems. Never before have we experienced such large numbers of bad stems, flowers and leaflets. This obviously made our testing much more difficult because we could be sure that at least some botrytis was going to be present when filling up the boxes. Therefore, and because we still hadn’t found a perfect protocol, we only used two boxes in our trial.
Peonies were cut May 26th and placed into the boxes, without putting them in water first. We mainly used Coral Charm as we thought it would be a better candidate for long term storage than the usual ‘The Fawn’ from former trials. Coral Charm is a variety that can be cut tighter than most others and will always open well. Also it was noted that Coral Charm showed no signs of botrytis on the flowers whilst in the lactifloras it was omnipresent. A few stems of other varieties were also added just to give a fast impression of what could be possible with them. We didn’t have too many stems available this year so they were only half full with some 250-300 stems in them and one set of Calcium Chloride (1kg in total) laid above them. The boxes were closed June 2nd and opened July 31st (after 9 weeks) and September 15th (just over 15 weeks).
The first weeks we left open all 6 membranes of each box to let oxygen levels decrease slowly. This was opposite to last year where we closed them all at the onset with the aim of going towards 5% oxygen in the air as fast as possible. Because we had some ‘grey flecks’ in the flowers last year we reasoned the fast decrease may have been a possible reason and thus wanted to avoid this.