How much light is too little

[abhikjha]

Hi everyone,

I live in Mumbai India which has tropical weather.

I have a decent collection of cactus which I acquired recently. Here are the pics attached.

All these plants are behind the glass window on a South facing side where sunlight falls over their bodies from 1:30 till 5:30. Summer here can be pretty intense (around 38 C max)

My question is whether this much light is good enough for them to grow and thrive or should I consider putting them outside?

Also, in order to grow these guys, do you want direct sunlight falling over their bodies or heated environment is good enough?

Best
AJ

[abhikjha]

I asked the question on heat vs direct sunlight because I understand that Gymnocalcyium needs direct sunlight falling over it to bloom but this guy just bloomed without it..

[DaveW]

The plants are in good condition so it depends how long they have been in those conditions? If quite a time then they are obviously thriving.

Gymno's can burn in very hot sun, however the difference with growing outside is you get better air circulation than in a greenhouse. Time to worry is when you see something going wrong or the plants are not thriving. Cacti need high light intensity, but can burn if it gets too hot and the air circulation is poor.

[abhikjha]

Thanks so much Dave for your replies.

As they are indoors, a ceiling fan is continuously on and windows are 24 hrs open for better air circulation..since, in evening it gets too hot here (disadvantages of being in tropical), I switch on AC as well for 3-4 hrs to get them cool with 25% of window open and door unlocked.. not sure if this is beneficial for plants though..

Some of these are relatively newly purchased and some of them are old, old ones have grown relatively well till now (fingers crossed). Few days ago, I accidentally knocked A Asterias and Melocactus and was glad to see both of them well rooted. I understand these are relatively difficult plants to grow so I can assume others are doing good as well..but I guess I need to pass them through the worst weather which is rainy season (3 months of non stop heavy downpour) to see the effectiveness of my growing methods..that time they will remain indoors and AC running will be slightly for longer period..

Any views on this or suggestions?

Cheers
AJ

[DaveW]

Generally speaking good air circulation is essential in direct sunlight to prevent burning. Warmth in itself is not such a problem, unless really excessive.

https://cactusway.com/why-is-my-cactus- ... 0hot%20sun.

[abhikjha]

Thanks Dave for your reply and sharing the link. I actually am running AC in evening to cool the temp down to induce CAM as I understand that many such plants need cooler temperatures in evening/night for photosynthesis.. what's your take on this?

[abhikjha]

Just an update - on my South facing window, direct sunlight has reduced very much since last few weeks as sun is moving more and more upwards and direct sunlight when sun is at its peak gets blocked by building roofs. In nutshell, amount of direct sunlight falling over the bodies of cactus has fallen drastically if I place them on window. However, there is no dearth of heat . Basically it has very bright indirect light. My question is should I put them out in direct sun which could be super harsh (we have 35C which will gradually increase to 40C soon). If I need to use shade cloth, then the effect of this wouldn't be similar to keeping them inside the room near the windows?

Also at what low level of light, they will start etiolation? If I refer to this article, it means that bright indirect light is good enough to keep them healthy:

https://cactusway.com/does-cactus-need- ... ht%20light.

I am mainly growing Astrophytums, Melocactus, Discocactus, Gymnocalcyium, few Echinopsis, few haworthias, few euphorbia and few notocactus.