Relative Light Demand

[From0to10in2weeks]

Hi,

I am growing cacti and Lithops indoors on window sills behind a large east-facing window wall and a regular sized adjacent south-east facing window. The plants on the east-facing window sill get direct sunlight till about 11:30 am and the one in the south-east facing window sill till about 12:30 pm. I am in Berlin, Germany.

Since space is limited I am thinking which plants need more sunlight relative to others and how to optimise the arrangement accordingly. For instance, I know that Gymnocalycium baldianum prefers less direct sunlight than other cacti. And it seems to grow better since I moved it into a shaded area.

So, how would you (roughly) rank the relative light demands of the following species:

1. Mammillaria spinosissima ssp. Pilcayensis
2. Pilosocereus glaucochrous
3. Espostoa lanata (Peruvian Old Man)? nana? Melanostele (Peruvian Old Lady)? Cephalocereus Senilis (Old Man Cactus)?
4. Gymnocalycium baldianum
5. Espostoa guentheri
6. Espostoa blossfeldiorum
7. Mammillaria (rekoi leptacantha?)
8. Trichocereus terscheckii
9. Opuntia monocantha f. monstruosa variegata (Joseph’s Coat)
10. Melocactus matanzanus
11. Tephrocactus Geometricus
12. Crassula Hybr. - Buddha's Temple
13. Ferocactus stainesii v. pilosus
14. Echinocereus rigidissimus
15. Ferocactus viridescens v. littoralis
16. Notocactus schlosseri
17. Astrophytum ornatum
18. Mammillaria bocasana
19. Mammillaria elongata
20. Lithops various

Thank you. Best.

[7george]

The question is very broad and a dissertation can written on this topic. So do not be surprised that no one wants to start enlighten this topic. I'ii just mention some aspects as I also grow my cacti mainly on windowsills.

Most sun demanding genera are Asrtophytum and Ferocactus so these should take the brighter spots with longest exposure. Maybe Espostoa stand next to them if not first in row. For Pilosocereus glaucochrous -- also maximum sunlight.

Next are different Mammillaria and these with fur or thick spines will need more sun.

8. Trichocereus terscheckii - young potted plants would need some shading but adult ones rather full sun.

14. Echinocereus rigidissimus - this one is also full sun lover but young will need some shade. Also sharp moving outdoors or to other (western) exposure can cause sunburns as for above species not covered by spines or hairs.

16. Notocactus schlosseri - rather full sun but with afternoon shade.

4. Gymnocalycium baldianum - most Gymnocalycium species grow under shrubs so would better feel under partial shade.

12. Crassula Hybr. - Buddha's Temple - this will be OK on eastern window or for shorter sunshine hours.

Almost all of the species can be acclimated for different light conditions after graduate shading and keeping on permanent spot but this will affect growth rate and producing of flowers.

[keith]

20. Lithops various

50% shade in almost coastal CA probably the same in AZ, actually everything in Pots needs shade in AZ

[7george]

Shade percentage is not something constant even for one city. During last weeks the sky here is so murky because of fires smoke (coming from US and British Columbia) so I removed all shading from over my cacti. I guess this will prevent even some blooms because even the temps went down.
I have to start complaining about climate change.

[From0to10in2weeks]

The question is very broad and a dissertation can written on this topic. So do not be surprised that no one wants to start enlighten this topic. I'ii just mention some aspects as I also grow my cacti mainly on windowsills.

Most sun demanding genera are Asrtophytum and Ferocactus so these should take the brighter spots with longest exposure. Maybe Espostoa stand next to them if not first in row. For Pilosocereus glaucochrous -- also maximum sunlight.

Next are different Mammillaria and these with fur or thick spines will need more sun.

8. Trichocereus terscheckii - young potted plants would need some shading but adult ones rather full sun.

14. Echinocereus rigidissimus - this one is also full sun lover but young will need some shade. Also sharp moving outdoors or to other (western) exposure can cause sunburns as for above species not covered by spines or hairs.

16. Notocactus schlosseri - rather full sun but with afternoon shade.

4. Gymnocalycium baldianum - most Gymnocalycium species grow under shrubs so would better feel under partial shade.

12. Crassula Hybr. - Buddha's Temple - this will be OK on eastern window or for shorter sunshine hours.

Almost all of the species can be acclimated for different light conditions after graduate shading and keeping on permanent spot but this will affect growth rate and producing of flowers.

Oh no. I had totally forgotten that I posted this question! Thank you so much for answering. And sorry for the late response.

Yes, I figured this is going to be tough. So, even more thanks for taking the time to address the question.
Providing afternoon shade is no problem with East and South-East facing windows.
Most of them are still rather small (#1 - 9, 12, 14, 15, and 18 are in 6 - 8 cm dia pots). The biggest is #13 with a 15 cm dia pot and about ~12 cm diameter (without the spines). The Melo and Astro are also pretty big.

The Crassula Hybr. indeed got majorly sunburned when exposed to full sun in the east-facing window even after an acclimatization period over 2 weeks. Now it’s back to shade with only very early morning sun. It’s budding like crazy though...

Why do you think that being on a permanent spot is important? I’ve actually been rotating some of my pots every week to give each a chance to be in the first row for max. light exposure.

Thanks. Best.

[From0to10in2weeks]

20. Lithops various

50% shade in almost coastal CA probably the same in AZ, actually everything in Pots needs shade in AZ

I doubt that I will have to shade the Lithops. The latitude of Berlin is halfway between Calgary and Edmonton, Canada. So, too much light is probably not the issue.

Best.

[7george]

===
Why do you think that being on a permanent spot is important? I’ve actually been rotating some of my pots every week to give each a chance to be in the first row for max. light exposure.

I have the same problem with not enough sunny spots at windowsills but try to keep plants at the same position longer, esp. if expecting flowers the same season. Feels like moving stresses many of them during active period. But if just moving forward or backwards at the same window is OK.