Rot segment in Opuntia and more

[mmcavall]

I have two cacti with some problems.

First, this Opuntia (any guess on which species is?). The lower segment is whitering and some parts are rot. The upper segment is okay.
What would you reccomend me to do? Just let it as it is, and see what happens, or should I cut the upper segment, let it callus and put in the soil again? Or something else?





Also, this guy bought in a supermarket (any guess on which species is?) is kind of rot/soft/seared in the lower part, but its "head" is growing fine, with new spines...do I need to do something?




Thanks in advance

[teo]

Looks like Polaskia chipipe for #2 - the skin pattern is rather typical.

[adetheproducer]

I would remove the healthy pad and re-pot in a much more mineral based soil mix so the soil holds much less water, I use a pure stone based mix for my opuntia which works well. Just twist and snap the pad off it should detach it's self at the joint. The polaskia looks quite ill, is it very soft like rotten fruit or a bit squishy like say an old potatoe? Is it very soft and rotten it might be too late, you could try cutting the healthy tip of with a sharp knife and re-root it again in a mineral mix but there might not be enough healthy stem to survive without roots for long. If it's more firm and just discoloured repot into a dry mineral mix let it rest for a week or two then slowly give it water in increasing amounts and let it dry thoroughly before watering again rather than a full soak to find the sweet spot for how much water it wants but always let it dry between watering.

[mmcavall]

Thanks teo and adetheproducer for repliying

Well, the Polaskia is more like and old potatoe. It has passed the last 10 days without water, and it looks better now than it was about 20 days ago. So it would be the case of let it grow in a more draining mix and see what happens?

The Opuntia, I'll detach the pad off and reppot. The mix is already very draining, but I would be interested in try growing some plants in a more mineral soil, that would be new to me, and this guy can be a good start.

thanks

[adetheproducer]

Yeah give it a go in more draining soil mix you might be lucky.

[greenknight]

the Polaskia looks over-potted, I recommend a smaller pot as well as a freer-draining mix.

[mmcavall]

thanks again adetheproducer

and thanks Spence: indeed, this potting mix is not a good one, I'm gradually reppoting my plants. I'll reppot the Polaskia in a smaller pot, but...why do the size of the pot matters? I mean, I've seen it here in the forum, the idea that the pots must not be too large, because it is not good to small plants... but I don't understand why. Provided that the potting mix is good, what could be the effect of pot's wall that are far from the roots?

[greenknight]

Why is over-potting bad? I think it's mainly because of this: the soil in the bottom of a pot remains saturated for a time after watering - http://gardening.stackexchange.com/ques ... ater-table" onclick="window.open(this.href);return false;

If the pot is not too large, the plant soon takes up enough of the water to end this saturated condition. Over-pot, and it remains saturated in the bottom of the pot for a prolonged period - water fills all the pore spaces, there's no air down there. Airless conditions lead to the growth of bacteria which don't use oxygen - in other words, the soil sours. I could go into a long explanation of the chemistry involved, but I won't - let's just say that only swamp plants are adapted to thrive in those kinds of conditions.

Using a very coarse, free-draining potting mix reduces this problem, you might get away with an oversize pot. You can also use wicks dangling from the bottoms of pot to draw out the excess water. Mainly, I just avoid over-potting. If I have to use a larger pot for some reason, I put some good-size rocks in the bottom to take up the excess space so there's less potting mix in the saturation zone. Make sure the potting mix gets around/between the rocks all the way to the bottom of the pot, or you just move the saturation zone higher.

[mmcavall]

Thanks Spence for your explanation! The cactus is already in its new - and much smaller-pot