Arum decline

Arnold Trachtenberg via pbs pbs@lists.pacificbulbsociety.net
Thu, 23 Jan 2020 06:28:27 PST
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 
>-------------- 
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