Arnold, Based on your venting description, we can't rule out temperature stress for your Arum plants. Also, since ammonium from organic fertilizer is the primary source of nitrogen for your plants, ammonium toxicity is a strong possibility. There are plenty of explanations of ammonium toxicity online as it relates to cool winter greenhouse temperatures and organic fertilizers. Nathan At 06:28 AM 1/23/2020, you wrote: >Nathan: The greenhouse is a lean -to. Tucked in >against the house. It faces south but early >morning sun is blocked on east side by one of >the lean to walls. I have a temperature >controlled ridge vent that opens at 50 >F. Radiant floor heat comes on at 45 F. Two >small 8" fans are on 24/7. The ridge vent is >open almost all the time during day time >hours. Temps can get to 60 during a sunny day >at this time of year. Here's the fertilizer I've >used. Has a good source of nitrogen. >https://downtoearthfertilizer.com/products/… >Arnold -----Original Message----- From: Nathan >Lange <plantsman@comcast.net> To: Pacific Bulb >Society <pbs@lists.pacificbulbsociety.net> Sent: >Thu, Jan 23, 2020 12:02 am Subject: Re: [pbs] >Arum decline 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.pacificbulb/ >http://society.net/pipermail/pbs/…> > ><http://lists.pacificbulbsociety.net/pipermail/pbs/…> >_______________________________________________ >pbs mailing list >pbs@lists.pacificbulbsociety.net >http://lists.pacificbulbsociety.net/cgi-bin/… >_______________________________________________ >pbs mailing list >pbs@lists.pacificbulbsociety.net >http://lists.pacificbulbsociety.net/cgi-bin/… _______________________________________________ pbs mailing list pbs@lists.pacificbulbsociety.net http://lists.pacificbulbsociety.net/cgi-bin/…