Lopsided Notocactus

[MikeInOz]

Turning can produce temperature changes for buds on that side since the sunny side is warmer than the shaded side Mike. It depends on how sunny a climate you are in. No doubt it is warmer in Australia than the UK.

Because a Neoloydia is not affected by turning does not mean all cacti are not. Also the problem in greenhouses can be burning if the normally shady side is turned to the sun. No doubt your plant has been regularly turned so it in effect has no "sunny side".

Yes as I said you only turn if there is no possibility of damaging the plant. If it is partly shaded - as mine need to be during summer - there is no problem turning them and there is no decrease in flowering. If they are in full light, then you can turn them at the start of the season before the sun gets too high. Turning them when they will be exposed to direct or very bright light soon after will have expected consequences.

[tasuccs]

Leaning is probably happened due to very soft soil when there's no firm support at the base of the stem. IMHO I'd recommend to change commercial peat substrate to a bit more mineral and/or to add upper covering of the soil with grit. Don't put the base of the plant dipper!

I do think it's both leaning and tipping over - as for why it's tipping I think you hit the nail on the head. The soil is a custom mix from a specialty nursery so not as peaty as it looks but still relatively soft & fine, and the pot is too small. I can see that the cactus has shifted since it displaces soil. When I pot it up I'll "thin it out" with some grit and top dress while I'm at it. That should help keep it steady even if it does continue to grow off center. Great idea, thanks!

As for it leaning towards the sun, I appreciate the input and lively discussion! Too many posts to reference but I've turned it around since right now the sun is relatively weak and low angle. Once the sun gets higher up and more intense I think I'll let it stay put so I don't have to worry about sunburn.

[7george]

You just confuse the plant by this often rotation.

No. You can't confuse a plant. It responds to it's environment. I turn my plants which lean too much. It's keeps them straight. I have a few which have already been turned 3 or 4 times since the start of the season and they are not confused.

Keeping cacti strait is an obsessive idea. Cacti are not like other plants. Some of them just crawl on the ground and bringing them straight up ... You'll get used to this when your collection expend to hundreds of plants and will be no time for fixing the angles.

[MikeInOz]

You just confuse the plant by this often rotation.

No. You can't confuse a plant. It responds to it's environment. I turn my plants which lean too much. It's keeps them straight. I have a few which have already been turned 3 or 4 times since the start of the season and they are not confused.

Keeping cacti strait is an obsessive idea. Cacti are not like other plants. Some of them just crawl on the ground and bringing them straight up ... You'll get used to this when your collection expend to hundreds of plants and will be no time for fixing the angles.

Yeah I'm not talking about plants that naturally lean as part of their natural form like many Echinocerei etc. But I don't want a Mammillaria leaning so much that one side touched the edge of the pot. It looks ridiculous and I'd rather not grow it if I had to put up with that. Luckily, I don't.
(I already have hundreds of plants. I only turn the ones that need it, and that is a small percentage). Turning also gives me more - and more even offset formation. Sometimes, turning 180 degrees once/year at the start of the season is all that is needed.

[tasuccs]

Thought I'd update since I had a chance to explore what seems to actually be a remarkable phenomenon over the past couple of months - this cactus seems to be able to lean itself back into the sun in a matter of days!

I posted this question originally not because I was so interested in symmetry, more concerned about my new young cactus tipping over. I'd say it's adequately stable after repotting and top dressing, but had decided to turn it around anyway to see if it would "correct" the slight lean it frustratingly seemed to still have even after I was sure I righted it. After a few times turning it away from the sun and walking by a week or two later scratching my head thinking, "I'm sure I rotated this? Why is it leaning that way again?", I did a more "controlled" experiment, and tracked it more carefully by marking exactly which way it was leaning after turning. I can now confirm that this young cactus is in fact tilting itself within a matter of days, so that the top is facing the sun again. Doesn't seem like the axis is tipping, so much as the side closer to the sun gets less engorged, and the side further away more so. Pretty amazing!

[greenknight]

Now you know how often you'd have to turn it to make it grow straight - or you could just enjoy it with a jaunty tilt, the way it wants to grow, since it's clearly not going to tip over. It's pointing itself at the sun!

Scientists have been puzzling over this forever. I learned years ago about how the plant hormone auxin caused plant cells to elongate more in lower light, which helps to explain both turning toward the light and stretching in low light. It was not a complete explanation, though, today they're finally getting a handle on the full complexity of this response: http://www.plantcell.org/content/26/1/38

[DaveW]

Its an indication that most of the light strength is is coming from that direction, such as a window for instance, rather than a more even spread of light in say a greenhouse. As Spence says the dark side of a plant grows quicker in poor light so it leans towards the light and in poor light both sides grow faster resulting in what we call etiolation.

[EdekaReweAldiLidl]

I also rotate my plants every now and then. Not 180 degrees though but 90 degrees. It keeps them from leaning

[greenknight]

Better to turn them 120 degrees, one third of a full rotation. That's for all plants, not just cacti.