Orchid - Yellowing Leaf and Possible Algae

Mark234(3a)April 2, 2014

Hi all - I have a phalaenopsis for which I have 2 questions. First, recently I have noticed the growth of a green substance on some of the potting medium and pot sides. Second, the largest lower leaf of the phal has begun to turn yellow. I have posted some photos below. I would appreciate any advice from more knowledgeable folks.

Some context: The orchid seems quite young, as the total leaf span is about 6 inches. I got him from a lady at work who wasn't sure how to care for orchids. There was a tiny, dried up spike when I got him, which I cut off. I have kept the plant in a small greenhouse all winter, temp thermostatically controlled to 25 C at night and 29 C during the day. Single grow light on 14 hrs/day. RH is kept between 55% to 75%. The roots were rotting badly when i got the plant; I trimmed off the rotted parts when I repotted. Potting medium is repotme's http://www.repotme.com/orchid-potting-mix/Orchid-Mix-Phal-Dark.html and the pot is their Oxygen Core Dual Pot - 4.25". I water with filtered water with Schultz Orchid Food 19-31-17 at their recommended strength. Sometimes I add a couple drops of SuperThrive. I water whenever the top sphagnum moss is nearly dried out but not quite so - this can be as frequent as every 2 days to as little as once a week, depending on environmental factors (probably RH & dewpoint and maybe how much the orchid draws). I have a small computer fan blowing lightly in the greenhouse 24 hrs/day. I am deliberately keeping the temperature above 25 C to encourage vegetative growth and prevent the stimulation of a flower spike, as I want the orchid to increase in size and strength so that when it flowers it flowers well. I plan to drop the temperature to 20C/24C in the fall to encourage a flower spike, assuming I have gotten the plant to vegetatively grow well during the summer. A new leaf started a couple weeks ago, and I see 2 new roots forming slowly. I can't see underneath to see the condition of those roots.

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Mark234(3a)

This leaf is completely shielded from the light. It is now turning yellow. From browsing online I have read that this can mean 2 things: it is totally normal and not a concern; or it is a sign of root rot and very serious. Any thoughts?

    Bookmark   April 2, 2014 at 2:25PM
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Mark234(3a)

Here is the green growth I have noticed recently. It is forming particularly on the sponge rock, staining it green. I have read that maybe this is algae, and is not bad as long as rot doesn't develop. Other sources say it is bad and can cause problems down the road if not ridden of.

    Bookmark   April 2, 2014 at 2:26PM
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Mark234(3a)

Another view of the green staining on the growing medium.

    Bookmark   April 2, 2014 at 2:27PM
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Mark234(3a)

Last photo - where the phalaenopsis lives & overall shape.

    Bookmark   April 2, 2014 at 2:29PM
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philpet

Looks ok to me,the leaf is yellowing from the tip perfectly normal,I would suggest you put some extra holes in the side of the pot though for extra ventilation, this can be done by heating a nail or screwdriver. The green substances is maybe from being moist,the extra holes will help.dont worry so much your plant looks healthy to me.Velleta

    Bookmark   April 2, 2014 at 4:06PM
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Mark234(3a)

Thanks philpet for the feedback. The leaf has continued to yellow. It looks like it is getting ready to drop off. All the other leaves look normal. So it seems likely this is just normal leaf aging as opposed to unhealthy roots.

    Bookmark   April 3, 2014 at 10:00AM
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philpet

Mark,phals drop bottom leaves when they begin to put out new one,its a cycle.the only time you should worry is if they drop more than one or two and if the leaf starts to yellow at the base where its attached to the stem,this would indicate a fungal or bacterial infection.your plant from what I can see looks healthy and has a few green root tips,which shows it is growing,so its perfectly healthy.just continue with the care your giving and watch that you don't over water this will rot the roots also you can give it a bit of fertilizer about once or twice per month and you should be fine.your doing great already.Velleta

    Bookmark   April 3, 2014 at 11:23AM
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Mark234(3a)

Thanks Velleta for the input, much appreciated.

    Bookmark   April 3, 2014 at 12:47PM
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