Light level tolerance

[Zoom]

Can anyone tell me if if there are differences between the cacti genus in their ability to cope with different light levels?
When I tried reducing the length of time my u.v boards were switched on for, I observed in my collection that all the Mammillaria seem to cope with any position in my cacti room but the Echinopsis I put furthest from the window became etiolated.

[habanerocat]

I don't think there are any hard and fast rules. But generally there's a few rules of thumb that I use. I know a lot of people won't agree. There will always be exceptions.

Firstly, seedlings like a bit of shade. Normally starting life under a mother plant or rock, they'll only need full sun after a few years.

Very spiny and fluffy plants like a lot of sun as they are naturally shaded, but like you said Mammillarias don't seem to be over fussy.

Columnar and tall plants like Opuntia like plenty of sun or they'll just get etiolated and fall over.

Cacti that grow at high altitude on barren ground again generally like full sun whereas small cacti that grow in grass and in forests not so much. Desert plants again full sun.

Cacti that grow by the sea tend not to be frost hardy (like most columnar cacti) and like it warm with plenty of sunshine.

So generally it's plenty of sun all round except for seedlings unfortunately.

[el48tel]

I don't think there are any hard and fast rules. But generally there's a few rules of thumb that I use. I know a lot of people won't agree. There will always be exceptions.

Firstly, seedlings like a bit of shade. Normally starting life under a mother plant or rock, they'll only need full sun after a few years.

Very spiny and fluffy plants like a lot of sun as they are naturally shaded, but like you said Mammillarias don't seem to be over fussy.

Columnar and tall plants like Opuntia like plenty of sun or they'll just get etiolated and fall over.

Cacti that grow at high altitude on barren ground again generally like full sun whereas small cacti that grow in grass and in forests not so much. Desert plants again full sun.

Cacti that grow by the sea tend not to be frost hardy (like most columnar cacti) and like it warm with plenty of sunshine.

So generally it's plenty of sun all round except for seedlings unfortunately.

That is one super set of guidelines

[ralphrmartin]

Years ago, I wrote an article for the journal about how putting various cacti under double glazed security glass ( a conservatory roof) caused Suclorebutias in particular to get quite etiolated (presumably due to lack of UV) while this happened much less to e.g. Rebutias and Aylosteras.

On the other hand, having moved to North Wales with much better light in general than when in Cardiff (both places under similar glass), I found that the Aylosteras got much stronger spines.

Aylosteras grown outdoors over the summer also developed much stronger spination in Cardiff than ones in the greenhouse. There would have been rather more light and no glass to block the UV (as well as other environmental differences in temperature, fresh air, watering, etc - which is why it is hard to pin down some difference to some single cause).

Overall, though, both the amount of light in general, and its UV component, can lead to significant differences.

[Zoom]

Ok, thank you for your views habanerocat & ralphrmartin.
If anyone else has experienced cacti exhibiting different reactions to light levels depending on Genus, then please share your results.

[SimonT]

Generally, brighter areas give stronger spines, more compact growth and better body colouration.
But the details vary a lot. It is quite informative to say grow a few plants of the same species under different light conditions to see how they respond. Spare seedlings are good to use for this.