Hi Arnold, How well is your greenhouse ventilated? Your plants remind me of how my outdoor Arums look like near the end of their growing season as temperatures warm. Ten days ago, high temperatures near you in New York were in the mid to upper 60s F (18-21C). Your greenhouse could have easily exceeded 80F (27C). The symptoms in the pictures are consistent with Arums experiencing brief high temperature and/or water stress possibly exacerbated by the longer days and increased afternoon light levels provided by the LED lights during the warmest hours of the day. You mentioned this happens every year. There has likely been at least one similar temperature spike during each of the past few years some time from mid December through mid February (easy to look up). Also, to make matters worse, you mentioned using an organic fertilizer. Most potted plants prefer a combination of ammonium and nitrate nitrogen. As far as I know, most organic fertilizers don't include any nitrate nitrogen. This can easily lead to ammonium toxicity especially with average cooler winter temperatures below 60F (15C). Your Arum leaf symptoms are consistent with ammonium toxicity. The University of Florida recommends avoiding all ammonium based fertilizers for potted calla lily production. Recommendations: 1. Based on your lighting description, switch the LED supplemental lighting from PM to AM or discontinue use entirely. 2. Don't extend the natural photoperiod. (Although, you mentioned they flowered in your basement under fluorescent lights.) 3. If you don't already, use automatic venting in your greenhouse. 4. Do what you can to keep the soil temperature down. Next year, consider using a larger/deeper pot. Your plants look crowded. 5. If you don't already have one, buy at least one min/max thermometer. 6. Don't move the plants outside in your USDA zone 7A climate. You might be able to pull it off some years if you have some extra plants to experiment with. 7. Moving the plants under the bench should not be necessary unless you need to lower their soil temperature. 8. Definitely change fertilizers or at least supplement with a nitrate source. I hope this helps, Nathan At 07:20 AM 1/21/2020, you wrote: >I've had these Arums for a number of years. A. palaestinum, A. >korolkowii and an Arum I was given by a colleague in Puglia, Italy. >The soil has been changed and pots sterilized more than once. I feed >with an organic fertilizer Down to Earth which is a blend of organic >components. I have them under some T-5 LED lights in a cool >greenhouse not below 45-50 F. Any suggestions would be most >appreciated as to how to correct this condition. This has occurred >for 3-5 years. The initiate growth and around this time of year the >leaf wilt appears. Thanks in advance.Arnold New Jersey >-------------- ><http://lists.pacificbulbsociety.net/pipermail/pbs/…> ><http://lists.pacificbulbsociety.net/pipermail/pbs/…> _______________________________________________ pbs mailing list pbs@lists.pacificbulbsociety.net http://lists.pacificbulbsociety.net/cgi-bin/…