Split leaves on many Paphs & Phrag

[Dandrobium]

Hey all!

I have a small collection of about 20 paphs & phrags (mostly seedlings) and 15 or so other genera. I live in a northern climate and grow in an old leaky sunroom. The slippers mainly grow on the top tier of my steel wire shelving unit, lit by a 4 bulb T5HO fixture. The middle tier is lit by natural light only. To try and keep my plants warmer & more humid in winter, I bought a clear vinyl cover for it. It set me back quite a bit () but it is working at both jobs I had pictured for it.

Here's the problem: It seems that since I have changed from an open air shelf, to enclosed, many of my slippers are experiencing leaf splitting (or at least the onset of splitting). Humidity has increased from 50% average to 70% average during the day, 50% at night. A muffin fan circulates air inside the enclosure, with slight movement of the leaves of larger plants. Temperatures are 72-75 daily, 58-64 evening.
I water all plants from below using stored rainwater, and soak the media (bark, perlite, sphag chunk mix) every 3 days (nearly dry throughout). I rarely fertilize in winter, maybe 1-2 times per month.

What could I change in my culture practices to avoid this leaf splitting? Plant growth is great, otherwise! Thanks for your help!

[silken]

[Leafmite]

I hope you find the solution to this. Good luck!

[Ray]

And newly-growing leaves splitting, or is it those that were already on their way when you made the change?

[Dandrobium]

Yes, there is some brown-line discoloration happening at the centre of a number of newer leaves, which will eventually split. I'd say this affects about 20-25% of the seedlings on the upper tray. I don't mist the leaves at all and there is typically no water sitting on the leaves as I soak the medium from below.

[silken]

4 HO T5's seems like a lot of light for Paphs unless they are far above them. But I am not a real good Paph grower, so I may be wrong.

[katrina]

If the HO T5s are the smaller wattage ones (ex 22 watts) then those should be fine for paphs as I'm growing some phals under them. The "big boys" though...the 4', 54 watt bulbs...yikes...totally agree those are probably too strong for many paphs.

As for the phrags...I don't grow them anymore (they hated my tap water) but most of my phrags I grew in catt level light so I guess it would depend on what species are being grown but most/many would be fine under the stronger T5s as long as they aren't too close to the bulbs and overheat. Pretty bright just no direct sun at all.

Either way, I think if the light was too much then there would be signs of burning more than anything else. I've always chalked leaf splitting up to low humidity but your humidity sounds fine. Is it possible you're under-watering? Maybe a lack of water in general is the cause? Just a guess.

[Dandrobium]

Most of the paphs are at the periphery of the light fixture, 12" below. They are the 4ft, 54W bulbs. But you're right, it is a fair amount of light for them. I have no leaf burning on any of the plants, so I figure it is at the high limit, but not excessive light. I have a couple inches that I could raise the fixture, so I'll try this.

Any other suggestions? So far this has affected the following seedlings (from memory):
kovachii
st. swithin
hainanense
jolly roger x james watson (newly added)
PEOY

Could the fan be having a drying effect that dries the media out too quickly? I forgot to mention, I also use heat mats, but they're not in direct contact with the plant pots. They're just to raise the temperature in the enclosure should it get too cold during the day.

---------- Post added at 04:37 PM ---------- Previous post was at 03:19 PM ----------

Here are some old pics from when I first setup the clear cover. I've moved and added plants since then

I'll try to get some shots of the split leaves next.

[wintergirl]

To me your top shelf looks a little on the too light side. Also I like to give my plants some fresh air, not sure how much fresh air yours are getting with the enclosure.

[silken]

Originally Posted by wintergirl

To me your top shelf looks a little on the too light side. Also I like to give my plants some fresh air, not sure how much fresh air yours are getting with the enclosure.

I agree, it seems bright for Paphs. I know some Phrag can take more, but mine seem to grow and bloom with less than that. I have a Kovachii cross which is growing well and a Paph. hainanense which is in bud right now and it is under 1 4 ft. HO T5 although in summer it does get some indirect sun thru the roof of the greenhouse, but not real high light.