Yes I have. It has always worked, although some additional remarks can be made. One year I’ve cut them down in the same month three times, to spread the flowering time in Summer. Each 10 days later meant far fewer flowers. Here in Belgium peonies usually flower in May, with most of the lactifloras around 20-30 May. Canary Brilliants is in the beginning of that period, around May 20 mostly. Cutting down June 1st works fine. June 10th and June 20th are progressively worse. This year was a remarkably cold and wet Spring and they only started flowering in June instead of halfway May. I thus waited until most of them had flowered before cutting down, hence this was around June 15th, when the last flowers were still on the plants. It seems the flowering time is no good predictor of the time to mow them down, I had very few flowers. It’s clear they have to be cut down around June 1st or possibly even earlier to have the blooming at the end of July, beginning of August. That means in a ‘late’ year, they’ll have to be cut down before their first flowering. This does limit the advantages of it somewhat you’ll surely agree. But such late years are a rare exception here, and becoming even rarer due to climate warming.
I’ve also tried to add some GA3 to the plants after cutting them down as this is often done to remove cold requirements. It didn’t help at all. I guess the secondary buds simply start growing because the main stems have been cut down. It is well-known from reports by some hybridizers that you can cut down the main stems from double (lactiflora) varieties early in the season to induce the secondary buds to start growing (which may be less double and hence more usable in a breeding program). That has to be done when they have only sprouted a few weeks at most. I think Canary Brilliants simply reacts longer to this phenomenon compared to other varieties and that it has nothing to do with cold requirements of the secondary buds.
I’ve not propagated my field of Canary Brilliants (some 750 plants) anymore. The flowers sell well in July/August, but the fact remains that that time of the year is when most people are on holiday and most florists close shop, thus demand is quite low anyway. And next to that July/August is, on average, warmer than May, thus they open rather fast. Canary Brilliants as a cut flower already opens too fast in my opinion, but in such warmer weather it’s nearly impossible to sell them easily. You cut them at the right stage in the morning. Put them in a vase and by evening they’re fully open, that’s too fast. Okay for some florists that have a wedding planned and so on, but for general customers that go to a flower shop and decide there what they’re going to buy, they are simply too far open. Given also that you have the remove all the foliage, which is quite a lot of work, I think it can only be a small ‘niche’-product. I’ve tried some other varieties as well this year, with GA3 added, but all I got was some leaflets and no flowers.
So, that’s the story up to now. I don’t think much will be added in the near future. Perhaps the tree peony High Noon has some genetics that may be used to proceed in this direction (or Oukan, one of its’ (more fertile?) seedlings), but I myself am not working on this.