Actually, for me, this is now a convenient way to able to cultivate and admire some of my favorite cactus species during the winter months at my home. I am now confined to staging my plants on a windowsill in my bedroom. (However I still maintain a considerable number of my favorite cacti in a greenhouse at Dan Bach’s Cactus Nursery that I visit from time to time courtesy of my cacti enthusiast friend, Michel Pillet).
On days when the outside temperatures are 60 degrees F + (most winter days here in Tucson) I open the window and transfer the trays they are in to a wrought iron stand just outside the windowsill to enjoy the fresh air and sunshine and they stay there until the temperature drops at eventide. I then bring them indoors so they are nice and warm throughout the night. Melocactus and Discocactus thrive under those conditions. Of course when the warm spring weather arrives (April here in Tucson) I stage my plants outdoors under 30% shade cloth and they remain in that environment until cold nighttime temperatures return (usually November here in Tucson).
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Indoors on the windowsill. Actually staged here as a group for photographing convenience.
Following is a Depiction of the set-up for staging my cacti (in full sun) on a wrought iron stand just outside my south facing bedroom window on reasonably warm days during the winter months. When the temperature drops at nightfall (or sometimes during the day) I slide the window open (the screen has been removed) and retrieve the trays one at a time (they are light weight) by reaching out through the open window and positioning them inside on the windowsill.
I have now replaced the mature Melocactus matanzanus and Arrojadoa dinae with transplanted incidental Melocactus seedlings that I feature in this thread - they make for lighter weight trays that are easier for me to handle and I still derive great pleasure from admiring their form and growth.