Cacti seedlings have gone brown/red colour

[Herbert0011]

Hey there all. I have hundreds of San Pedro, Echinopsis pachanoi (syn. Trichocereus pachanoi) seedlings.

Through the long winter they have turned a brown/red colour. I do not think it is sunburn as they have been kept in a reasonably dark place over the last 6 months with nothing even close to direct sunlight touching them. After 6 months of cold weather (around 10 degrees Celsius) we are now going into spring/summer here in Australia and after 5-6 weeks of reasonably warm weather (around 23 degrees Celsius) the seedlings are still brown.

Do any of you green thumbs have any idea as to what may be the problem. Please see attached photos. Cheers, thank you, Jaryd.

[hegar]

I do not believe, that the discolored seedlings are suffering from some kind of disease. They do look plump and otherwise healthy on the images submitted.
However, something is wrong. In my opinion, this a physiological problem. The plants do not have enough chlorophyll and the underlying colors (brown, yellow, etc.) are masking it.
I would try to subject the cacti to more light, much more light. However, be careful, that it is not accompanied by excessive heat.
Perhaps start with a short exposure like 1-2 hours a day and observe, if there are any noticeable changes. If a little green return to the seedlings, increase the exposure time by at least doubling it and eventually giving them the light hours equivalent to what the day length indicates.
You could also split the cacti into groups and compare the results, like it is done in a scientific experiment.

You mention, that the plants were kept in a reasonably dark place. This early in their development, these tiny plants will react much more to the removal of light than a larger plant. Also, are you sure, that the plants did not suffer a light cold damage? This will also make the chlorophyll seemingly disappear in many cacti. Excessive heat and perhaps even excessive amounts of light will stress the plants too, and those may also cause the healthy green color to disappear. Once the stress factor is removed, however, the plants will begin to look normal again.
Have your plants changed in their appearance since you posted the images?

Harald

[hegar]

P.S.: The main problem I see is, that you germinated the seedlings at the wrong time of the year.
One more thing I forgot: Some cactus seedlings will not look very green, when they first emerge. However, over time and with increasing size, these plants will assume the color of the more mature specimens.

Harald

[Herbert0011]

Hi Hegar I agree that there is a low amount of chlorophyll in them. The flash on the camera makes the cacti look more green than they actually are. They look much more brown/red with the naked eye. I also agree that gradually adding more light would be a good idea.

The cacti seeds were sown in spring time as temperatures approached above 23 degrees Celsius for germination. Over the next 4-5 months (spring/summer) they grew to their current height. As the colder weather approached they were moved inside where they went kind of dormant and did not grow any more. Now as the the warmer weather approaches again I am hoping they will begin to grow again and their colour returns.

[george76904]

Wait red? How much light are they getting currently? Stressed seedlings will turn red if they get excessive light.

[greenknight]

Seedling can be fairly red without it being a problem - enough light to make them pink or reddish is ideal, and they appear to have made reasonably good growth. They turn purple in really excessive sun.

They're old enough that they should be gradually introduced to more light, and allowed to dry out between waterings. Might need fertilizer, if the medium is low in nutrients.