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My Mesemb's seedlings (several species) are/were doing fine 20 days after germination. Some have already the first pair of true leaves.

I am/was very proud but... suddenly I noticed that some sedlings presents the following problem:

Their cotyledons are green and apparently healthy, but as you follow the "stem" in direction to the roots, it will appear kind of a "strangulation", and below that point, the stem is seared, very thin...and the plant will finally fall apart (although not drying out or dying, at least until now).

(Hope that you guys can understand my description of the problem, it is not easy when English is not your language)

So, what is it? Is this by chance the famous damping off?

Some of the cotyledons appear sunburned also, with white dots...is this really sunburn (they take good sun) or it is related to the problem above?

Thanks in advance

Perhaps etiolation? Falling over, but not dying? Hard to say without a photo, but you might not have a problem at all.

Are the plants in the sun? Although it is winter, they might be too warm. Most mesembs grow well with nighttime lows of 5C - 10C. Seedlings will grow at warmer temperatures because they have no choice, but they still might stretch in warm humid conditions. Bright sun and good ventilation is ideal, although you'll have to shade them if it is very hot.

ok, Iann, you are probably right.

They were etiolated in the very begining of germination, and now they take much more sun, I dont believe that they still needing more sun (some of the seedlings are indeed red at the margin of the cotyledons) but they can't revert the initial etiolation symptoms...

Night temps are about 15C and during the day, about 30C! (this week is incredibly cold, 8ºC during night, 18C during the day, and everybody is complaining because it is too cold...that's the end of winter here).

I spray water early morning and at noon, my doubt now is exactly about watering, whether is time to diminish humidity or not.

They take sun from 10 am to 15 pm, and good, very good ventilation.

I can't diminish the room temperature, so, let's see who will survive the summer (that was my first and last try with Mesembs, changing to Euphorbias and cacti now).

The only photo I can show now is in this thread, last photo, where Monilaria seedlings presents the problem I described.

http://www.cactiguide.com/forum/viewtop ... 16&t=37654" onclick="window.open(this.href);return false;

They'll be fine. Once the leaves get fatter, the stems will be hidden and the little plants will stand up. The plants in the photos look healthy.

Mesembs can stay in very high humidity for several weeks, maybe even a few months, but once they start to show true leaves it is best to bring them into fresh air.

Winter growing species in particular might struggle in the summer. You'll probably have to give them a lot of shade (definitely afternoon shade) and learn a daily spraying technique. Some might go dormant even in their first summer, like Monilaria.

iann wrote:They'll be fine. Once the leaves get fatter, the stems will be hidden and the little plants will stand up. The plants in the photos look healthy.

Mesembs can stay in very high humidity for several weeks, maybe even a few months, but once they start to show true leaves it is best to bring them into fresh air.

Winter growing species in particular might struggle in the summer. You'll probably have to give them a lot of shade (definitely afternoon shade) and learn a daily spraying technique. Some might go dormant even in their first summer, like Monilaria.

But if I give shade, will they etiolate?
Thanks again Iann

mmcavall wrote:But if I give shade, will they etiolate?
Thanks again Iann

Use a(n additional) shading cloth. They still get plenty of light to grow, but will be safe from the severe sun intensity.
I would not put them in actual shade.

Aiko wrote:

mmcavall wrote:But if I give shade, will they etiolate?
Thanks again Iann

Use a(n additional) shading cloth. They still get plenty of light to grow, but will be safe from the severe sun intensity.
I would not put them in actual shade.

Thanks Aiko, I understood.

For instance, the seedlings are on the lower shelf. Above them, there is the upper shelf wich has a shading cloth. When sun is not in the zenith plants receive direct sun. Probably don't need additional shade clothing.

I'll take some some pictures and post here.

So here you are the pictures.

First, a general view. The seedlings are in the pots inside the white tray, under this shade cloth that is not very closed as you may notice...



... below the upper shelf



so you wouldn't imagine too much sun but below it is possible to see how much sun they take at about 13 p.m. (about 30ºC / 90F):



I really don't know whether it is too much sun or not.

Now some close-up so you guys can see the general aspect of them:

Pleiospilus compactus response to the sun:



And the problems I stated above:

Pleiospilus bolusii stem "strangulated"



Marlothistella uniondalensis: sunburned????



New pictures of the healthier in this thread:

http://www.cactiguide.com/forum/viewtop ... 16&t=37654" onclick="window.open(this.href);return false;

Don't worry about them being sunburned already. If they burn, you will definately notice: they will be fully white, or just gone at all in one day's time!

Although your sun intensity could well be much higher than I can experience up here in Europe, but I think this all looks fine.

Thanks Aiko,
I think that while you were replying this I was uploading more pictures (of some of the remaining seedlings) in another thread:

viewtopic.php?f=16&t=37654

They look fine to me. I wouldn't be worried about giving them more sun, but I'd be crazy worried if it was 30C It gets to 30C here about once every five years and I throw sheets over the greenhouse, remove half the glass, and run lots of fans. Perhaps overkill?

iann wrote:They look fine to me. I wouldn't be worried about giving them more sun, but I'd be crazy worried if it was 30C It gets to 30C here about once every five years and I throw sheets over the greenhouse, remove half the glass, and run lots of fans. Perhaps overkill?

Iann, I have no choices. My greenhouse is kind of a high tunnel were wind passes through, lots of wind, I have nothing to open...(picture here: http://www.cactiguide.com/forum/viewtop ... 31&t=37648" onclick="window.open(this.href);return false;).

I don't believe that shade clothes would diminish the temperature significantly when room temp. it is about 35ºC...as I told you, we are in the end of the winter, so let's see what will survive the summer. Perhaps this experience will illustrate what happens when you grow mesembs in this kind of weather, since there are few experiences of south hemisphere growers in here the forum when compared to northern hemisphere growers.

For instance, my three Faucaria and the Trichodiadema densum are doing very fine. I'm impressed with their good growth during the last 3 months. Perhaps they are easier species...or mature plants dwell better than juveniles... anyway, let's see what happens the next months to these seedlings. I'll keep posting.

As for the "strangulated" stems, I had the same thing happen with some Fenestraria and Titanopsis I tried Spring planting. Aiko sent me a generous amount of seed (Thanks again, Aiko!), and the weather was cool enough, so I tried a batch. The results were not great, but there are some survivors Those that came up quicker and spent more time in the baggie developed long stems, part of which later shrank to just a thread. Looks to me like the extra stem was just converted into root - they're not supposed to have a long stem, after all!

We've had a few spells of above 30*C recently, having one now - those seedlings are not happy campers. They haven't grown much, I don't think anything was gained by the early planting except experience. I expect the Fall planting will pass them up.

Spence, your description " developed long stems, part of which later shrank to just a thread" fits exactly to what I observed.

Did these plant of yours ultimatelly die or still surviving?

I have some survivors of Dorotheanthus bellidiformis sowed in April. I remember that some of the seedlings presented this problem, but I don't know whether the survivors are those with the problem or not. Anyway, they are doing fine, very healthy, apparently not suffering from heat.

Yesterday I managed to open the lower part of the greenhouse plastic wall, providing more ventilation, this will help a little the mesembs seelings.

Most are dead, but some survive - the weather has not been kind to them. The biggest Titanopsis calcarea has that condition, and has clearly grown some. I'm thinking of covering up that shrunken stem with sand, on the theory that it's now a root.