Red Seedlings

[Holunder]

Hello experienced cactophiles,

I would be thankful for some advice with my stressed seedlings. I tried to move seedlings that grow long and thin closer to artificial light and seedlings that turned red to a less light-intensive place. In this photo, all seedlings have the same exposure. (The white dust is Diatom dust.)

red seedlings.jpg (269.86 KiB) Viewed 5319 times

Escobaria abdita look OK to me,
Copiapoa laui is a bit pale,
Escobaria missouriensis is long an thin with a green top and a red bottom part,
Glandulicactus uncinatus has become long and thin and red.

I probably kept them on the dry side, could that be the problem too?
What can I do better?

Regards
Holunder

[keith]

Hi, I guess I would add some sand and try and support the falling over tiny stems a tricky operation . Some cactus seedlings turn red this is a problem only if they stop growing.

From the picture it looks like none of them are getting enough light ? Nice rare species .

[Holunder]

Thank you Keith,
I have now supported them with some fine grit and will give them more light. My Luxmeter indicated they had around 4000 Lux, I could give them up to 8000 Lux. Is that too much?. Yes, they are funky species, I would be so sad if I killed them. Do you think that the red tint is a sign of stress that has nothing to do with too much light?

red seedlings2.jpg (246.73 KiB) Viewed 5294 times

[Holunder]

I found these older posts with some info which confuses me.

https://cactiguide.com/forum/viewtopic. ... ux#p305942
Iann wrote

I have no idea what your setup is like, but etiolation is caused by insufficient light relative to other factors, most obviously to temperature. Warm nights cause rapid and necessarily etiolated growth, as well as being stressful in other ways to most cacti. You'll probably never get night temperatures in a propagator down to outdoor levels in a desert, or get daytime light intensity equivalent to direct sunlight, but neither are necessary. 500 foot-candles for starting seeds, and 1,000 or so for seedlings after a few months can produce good results with sensible day and night temperatures. Much more than that will stress many cactus species, although some will take it. Some, like Ariocarpus, do extremely well with those light levels for 2-3 years."

"3,000 foot-candles will turn most cactus seedlings bright red very quickly, Hard to imagine you would get etiolation at those levels. Maybe constant high temperatures? I only get around 2,000 foot-candles in my overwintering box for 2-3 year seedlings, and that's only for a few hours of each day. Adult cacti will happily flower in these conditions."

When my Glandulicactus and the Escobaria missouriensis looked like etoliatiolating, I moved them closer to the light. Could the reason for long whobbly growth also too high night temperatures in germinations phase? (now 4000lux 12hrs / 20°day and 16-20°C at night /germination phase from 500-700lux increasing ca. 28°day and night)
Anybody some ideas?

[MikeInOz]

28C day and night is too high. The temp should be about 10C difference between day/night. I don't measure light but my seedlings are shaded with about 70% under full sun ( I guess than would make it more like 10,000 lux?? ) and there is no stretching. Make sure you have a balance of K and N also. K should be at least as high and preferably 2 times the N available to the plant particularly in low light.

[keith]

Rocks look good.

Warm nights cause rapid and necessarily etiolated growth, as well as being stressful in other ways to most cacti. "

Mike's right have a temp swing day and night. That helps with germination also but you don't seem to be having any trouble with that.

[Holunder]

Hi Keith and MikeInOz, on the next batch of seedlings I will definitely turn off the heating mat at night, then I will have about 27°C day /16-18°C night during germination. After using a little too high N fertilizer which caused some of my Astrophytum seedlings to burst, I now use an NPK 2.5+4+6 fertilizer diluted. Oh yes, no problems with germination, I need a greenhouse soon...

[greenknight]

Pink isn't bad - especially if the growing tip is green, in that case there's no problem. Darker red or purple means light is too strong. I agree about the night temperature.

[Holunder]

greenknight, do you think they still count as pink?
Escobaria missouriensis has some green tops with first spines and Glandulicactus looks slightly greenisch at the top.

[greenknight]

Overall, the color isn't too bad, though some individuals look a little more red than I like to see. Correct the temperatures and keep them evenly damp - don't let them dry out at this stage - I think they'll be okay.

[Holunder]

Thanks I´ll do that