As usual a short description about the season as this differs from year to year. Quite average this year, with peonies flowering at the normal time, from mid-may to the end of that month for the most part. It was also dry during the season with hardly any rain. Given that it was continuously dry we didn't spray with fungicides against botrytis. This is against the advice for long term storage of course, but in the long run most fungicides will be phased out anyway, the future is bound to be 'greener' and probably more 'organic'.
The calcium chloride sets laying on the peonies
The peonies were cut at the last days of May for the boxes, placed in the boxes (no prior water soaking) and left to dry for about a week in a cold storage. The calcium chloride sets were laid horizontally on top and the boxes were closed June 6th with all caps closed to decrease the oxygen levels fast. It took about a week for oxygen levels to go below 10%. Below are part of the measurements of oxygen (O2) and carbon dioxide (CO2). Given all the failures and the peony stems thrown away in previous years, we only used 4 boxes this time and filled them with the smaller ones. Box 2 was only half filled due to lack of enough stems. The Fawn was used again, but some stems of other cultivars were also added to compare. As were some bunches that had soaked up water. Temperature of the cold room was set at 0,3°C until Aug 2nd when it was raised to 1,8C. Aug 25th it was lowered again to 0,3°C. Some caps were opened when O2 levels went below 5% to raise it again. When this happened CO2 levels concurrently went down rather fast. Box 4 had one cap opened June 24th, closed again July 2nd. August 2nd, both box 3 and 4 had two caps opened.
|Starting date June 6th. Opening dates in yellow. Temperature and Relative Humidity was logged in box 3 & 4. Box 2 only half full and only 1 set of calcium chloride. Other boxes 600-700 stems and 2 sets of calcium chloride. na = not available (no measurement done)
What did we seen when opening the boxes?
July 29 the first one, box 2, was opened, the one which was only half full and which never went below 10% Oxygen due to this. All stems came out fully dry, no condensation at all against the inside walls or cover. So one set of calcium chloride seemed to be sufficient in this case. As it weighed approximately 1 kg at the onset of the treatment and ended up weighing some 2,3 kg at the end, we can assume that about 1,3 kg (or litre) of water was taken out of the air. From about 380 stems, only about 15 showed some damage due to 'grey flecks' as in 2021. Those were the few ones with the buds in the middle of the box, hidden below the foliage of the stems above. The other ones were all placed with the buds towards the sides and these were fine. This made us think that those few bad ones may have had too few oxygen perhaps? The ones that had soaked up water were also fine, contrary to our results of 2019, but there was an issue however. All peonies in the box had dried out leaflets when opening the box. The ones that went in 'dry' however could be rehydrated and the leaflets became fine again, whilst the stems that had soaked up water couldn't as the leaflets remained floppy and dry there. There was 0% botrytis on the stems, leaflets and flowers in this box. So we might call this a success, with the conclusions that no buds should be stored between the leaflets, only at the sides, and they shouldn't soak up any water before placing in the boxes. They opened fine in a vase when tested.
After long term storage and rehydrating. Left the stems that had soaked up water before being placed in the box, on the right the 'dry' ones that went straight in after cutting
Opening fine after long storage
A few days later, August 2nd, we opened box 1, which had more stems in it (550) and two sets of calcium chloride. We were obviously hopeful after the success of the first box. However... Whilst there was no condensation here either and no botrytis to speak of (except for a fews stems that probably were infected during harvest already), half of the buds had grey flecks again, as they did last year. Last year we assumed it was due to the oxygen level going too low at some point, but this year it hadn't gone so low, so we are unsure as to the reason. This meant a lot of work sorting them out unfortunately. Some of the added other varieties seemed to cope better than The Fawn: Rozella and Miss America had more good ones in comparison (some 10 stems each were tested for these varieties). Myrtle Gentry was bad. Bowl of Cream didn't show those flecks, but most of the outer petals had dried up and were ugly. Old Faithful was fine, but only the ones that went into the box 'dry', not the ones that had soaked up water beforehand. Another conclusion: whilst the oldest one in the boxes had dried about a week before closing the cover, the freshest ones had only dried for about three days and there wasn't any difference between them after the storage, so those 3 days are already sufficient.
Rozella showing the 'grey flecks' symptoms very clearly
As the other boxes had the same amount of stems in them, the same number of calcium chloride, had reached comparable levels of O2 and CO2 and were in the same cold room thus the same temperature, it was to be expected that those too would have at least 50% flower buds with grey flecks. Because the temperature in the cold room was too low for our other flowers we grow, we hadn't been able to use this refrigerator. Given the certain loss already of the peony stems in the boxes we raised the temperature in the cold room to 1,9°C so we could also use it for our other cut flowers (gladioli during Summer).
August 23rd we opened another box. Unexpectedly this one had fewer grey flecks on the flower buds, although they were still present to some degree. But, also unexpectedly, we did have a lot of botrytis here, about 2/3 of the flowers showed damage due to this fungus, and had to be thrown away. There was no condensation, but the flower petals felt 'wet', so relative humidity must have been higher, although not reaching 100% which would have resulted in condensation. The two sets of calcium chloride were not saturated, although they had soaked up an impressive 1,5 litre of water each.
Given that the other box would be comparable again, we were not particularly looking forward to opening it, most would be infected by botrytis after all. So we changed tactics: we lowered the temperature again to 0.3°C because we reasoned that the higher RH could only be the results of the breathing of the leaflets at the slightly higher temperature. Would we be able to lower the RH again by lowering the temperature?
The answer came when we opened the last box on September 16. No condensation again, the 2 calcium chloride sets had soaked up even more water, nearly 2 litres each. 95% of stems had to be thrown away due to botrytis. The few ones that had no infection were quite good, though not like fresh ones of course. Only few of them had grey flecks, although some may have been missed due to the heavy botrytis infection of course. Rozella and Old Faithful were the best ones of the 'other' varieties and better than The Fawn for sure.
Hardly a success, the last box opened...
And what about the Relative Humidity, were we able to bring it down again in this last box? The following graph shows both the temperature and the relative humidity.