The peony flower season lasts only a few weeks as we all know. Although the season has been advanced and prolonged by growing them in other places more South and North, year-round production is still not a viable option. They can be bought any time of the year, but if you buy them in between seasons, you may find them both expensive and the quality wanting.

What we wanted…

With fruits, mostly apples and pears, it is common practice to store them after harvest in special cold storage rooms where they can control the air contents (oxygen (O2), carbon-dioxide (CO2) and nitrogen (N)), together with temperature and humidity. This is usually referred to as Controlled Atmosphere (CA) and fruits can be kept there for several months without decreasing quality. It is normally done by lowering the proportion of oxygen in the air, thus the name ULO-treatment (Ultra Low Oxygen).

In 2007 an article appeared in a trade journal, Vakblad voor de Bloemisterij, wherein a grower reported to keep his peonies in such storage to be able to sell them several months later when no other grower would have any. Interested by this, we decided to try it out, together with PCS, a research station here in Belgium. So the following year I harvested some flowers and the PCS collected them here and did some tests. They had contacted the firm that did the treatment for the grower in Holland and were duly informed that the grower would not repeat it as it had shown too much problems, but they did give us the air composition. The air we all breathe contains some 21% oxygen, 0,03% carbon dioxide and the rest is nitrogen. The ULO-treatments tested were either 10% O2 and 8% CO2, or 3% O2 and 5% CO2, with a planned storage period of 12, 16 and 20 weeks, and then some tests at the beginning and at the end with normal storage. We used fully closed tubs to do the testing as these would not let any oxygen through. On the image below you can see a Palistore system on the left, which is essentially a plastic covering that does the same thing and which is used for somewhat larger volumes than those that can be placed in a tub, as you can see on the right.

It didn’t work out well. Many flowers had dried, some of the water they were standing in had frozen, there were several cases of botrytis and after storage they only kept for 3 to 4 days when placed on water. The main issue of these was botrytis.1 No further tests have been done here since then.

What we got…

There are always those that don’t give up after one try and last season some more research on ULO-storage of peonies was done in the Netherlands. It was discussed with peony growers a few weeks ago and a report of it just appeared in Greenity, an excellent dutch language trade journal with all issues freely available after a short delay of a few months, here’s a translation for those interested:

Ultra Low Oxygen (ULO) storage of peonies offers perspective.2

Paeonia truly is a seasonal product. At times that season can be very short due to hot weather, as it was last year. How to prolong the season? The first results of a test at CNB, a Dutch cooperative for mediation in flowerbulbs and herbaceous plants, shows that storage of flowers in ULO-conditions offers perspective.

“And June 1st all peonies had been harvested.” That’s how Ron Hoogeveen, mediator at CNB and specialised in peonies, summed up the 2018 season. It was the end of a strange springtime with a lot of cold early in the season, which made it look like the flowers would be two weeks later than usual. Eventually the hot weather in the second half of May made them catch up at lightning speed. This presented a lot of companies with two problems: too few cold storage room and too few helping hands.

It is customary for peony growers to prolong the season by keeping part of the harvest in cold storage to sell them later. A few weeks present no problems, but longer does: the foliage deteriorates and the buds don’t open as well. Thus at CNB the question arose whether ULO-storage might offer an alternative. CNB has a lot of experience with the storage method. The cooling and treatment facilities have special rooms for them, where lily and tulip bulbs are kept at extremely low oxygen levels, giving good results in floriculture. Those rooms are not an option for harvested peonies. Could it be done otherwise? Yes it can, and Yorick van Leeuwen, cultivation advisor at CNB, gave some details during the ‘Peony afternoon’ which took place December 19, 2018 at CNB in Bovenkarspel. Some 170 attendees were informed about the first results of his research.

Closed boxes

Van Leeuwen and Hoogeveen contacted a company that delivered closed boxes in a standard ‘cubic metre’ size wherein ULO-conditions can be created. Some tests were done with these last season. The boxes contain six membranes that let oxygen out, but not in.

Two growers cooperated with the project, they both filled six boxes with peonies. The flowers were placed in them either May 24 or June 4. Every box contained 700 stems. When filling the boxes, two requirements are essential, according to Van Leeuwen. “The crop must have been cooled down already to a temperature below 2°C. Next to that the crop must be completely dry. If this isn’t the case, then moulds and bacteria may give damage. This is because these do grow normally under ULO-conditions.”

The flowers were kept up until 14 weeks after closing the boxes. The following varieties have been tested: ‘Kansas’, Sarah Bernhardt’, ‘Gardenia’, ‘Alexander Fleming’, ‘Bridal Shower’, ‘Monsieur Jules Elie’ and ‘Dinner Plate’. For comparison purposes these varieties have also been placed in normal cool storage.


The peonies were taken out of the boxes after five weeks onwards. Van Leeuwen showed each time both what the peonies from ULO and the normally cooled ones looked like. The difference was clear. The ULO-peonies looked fresh, including the foliage. Even after 5 weeks in normal cooling those peonies showed dull, less fresh. After the treatment Van Leeuwen placed the flowers on water, without any further additions. Most flowers opened well.

Even varieties like ‘Monsieur Jules Elie’, which had been in storage for 14 weeks, and ‘Sarah Bernhardt’, twelve weeks ULO, showed well. September 14, Van Leeuwen still had magnificent peonies blooming with him. Overall Van Leeuwen determined that in some cases there was some decay due to black mould or botrytis, but those were low proportions.


Van Leeuwen emphasized these are merely the results of only one season. These however are thus that CNB would like to continue them. “Next season we’ll continue and we’re looking for interested growers that want to cooperate. They can contact me or Ron Hoogeveen. One thing we’d surely want to research further are the effects of pre and post treatment agents.”

‘Peonies every single auction day’.

Auction employee Mario Heemskerk from the Aalsmeer branch of Royal FloraHolland gave a short overview of the 2018 season. Heemskerk said that every single auction day peonies were traded. In January the season kicks off with flowers from the Southern Hemisphere, after which the first flowers from Israel arrive, followed by different regions in Italy and France.
The short, heavy harvest in the Netherlands had big consequences for the auction, Heemskerk reported. “We received many complaints about the harvest stage of the flowers. The flower judges didn’t have an easy time. Part of the flowers had opened too fast and must have gotten too much heat during storage or transport.”
Till October peonies have been sold that were stored this long, after which, from the end of October onwards the first flowers from Chili appeared before the auction clock.

  1. Blindeman, L. “Gebruik ULO voor bewaring pioenroos.” In: Jaarverslag snijbloemen, 2008, PCS, pp. 18-23[]
  2. Dwarswaard, A. “ULO-bewaring pioenroos biedt perspectief.” In: Greenity, January 3, 2019, pp. 16-17.[]

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