you have a sunny space for it indoors, no need to cut. make sure not to get any hitch hikers.

get a systemic product. and treat the pot outdoors a week or two before you bring it int he house...

https://duckduckgo.com/?q=systemic+plant+indoor+treatment&t=ftsa&iar=images&iax=images&ia=images

these nothing worse than battling bugs in the house all winter long...

watering might be tricky .... it will slow down significantly indoors in winter... so will need less water.. let the media near dry between waterings...

do not place it too near a heat register.. dry winds wont make it happy ...

and if possible .... some plant lights will really help ...

what is the second pic???

ken

These are 3 yrs old now. Last year trimmed the one on the left. maybe a third. Definitely fuller. But when they were the size of yours didn't trim them. Had them in upstairs in front of dormer windows facing south. Dropped a ton of leaves but well worth the mess.

Ken_Adrian thank you for the info. I neglected to mention I have plant lights. How many hours a day would you suggest? Also the second pic is a close up of my red Mandevilla blossom.

getgoing100 - Thank you! I do have a sunny place indoors - or I may put it in my basement with plant lights. One of the other houzz members suggested systemic plant treatment before bringing inside for "hitchhikers".

KarenT - thank you. I may trim the long ends as I know it will be tempting for my cats when they see trailing vines-it's toxic. They didn't seem interested in this plant last year, but I did trim it a little bit. Thanks again.

@summerlee340, Ken is the expert. I bring them in when it gets fairly cold outside and even the indoors get cool. I find that they do not shed that many leaves then because the transition indoors gets easier (lower light outdoors, a little warmer indoors, you could almost fool them into thinking it is spring with grow lights).

I have not found the need to do any treatment and rarely found any pests on them. The one time I drenched them with a bit of soapy water, they promptly died. I would also not put them in direct sun in window right after bringing them in (it gets pretty warm indoors under direct sun). Just ease them in before giving them a sunny spot. Mine eventually die of overwatering indoors. They need very little water in the winter and I.......

getgoing100 thanks again. Good advice. I wrote to Ken about plant lights.

@petrushka (7b) Your balcony looks great. And hello neighbor! I like how you have supported the amaryllis leaves from flopping over.

Oh! :) they get floppy from the wind no matter how much i protect them. so i twist a stretchy piece if fabric in between each leaf and wrap it around the stake sort of like on a spiral. so even very tall leaves can be held up. it works!

and i slip a cut off clear bottle over the young leaves to protect the neck..i’s funny looking but i have high wind on the balcony.

Yeah, wind is hard at work destroying everything pretty except brief respite during summer. My dahlias jeep losing limbs and have shabby leaves, the rose leaves are half burnt/dry, I am even staking crocosmias....I will have to study your staking methods for lillies, mine have been pretty useless.

I took a better pic : don’t quote me ;), but i take an old acrylic sock and cut it on a spiral, then stretch into long string; fold double and tie low on a stake . then start twisting a few times and catch a leaf between 2strings. keep going around each leaf getting higher until i fo full circle and then tie it high on a stake. if you use 2 stakes tou can do another spiral, keeping leaves looser. here here’s a better view

i keep forgetting to get some synthetic green fabric for cutting strings, like lycra or polyester. it needs to be elastic to give in the wind. cotton deteriorates very fast. green would be much less visible! cut off bottles protect leaves from bending out and breaking low quite well.

my leaves even in the sun get to 3‘ : totally unmanageable in the wind.

I tie up older thicker Mandevilla branches like that too: it really likes to spread wide!

and tropical Hibiscus too to keep them higher rather then wider.

and even tall Caladium leaves.

This is some sophisticated staking jujitsu! I will have to real study it a few times to figure it out. The damage is done for this year so I will be back next year with questions.

the twists between the leaves keep them separated and keep them in place quite firmly. just do a lot of twists. But with just 1 mid stem string they can still flop and break . so 2nd higher is better.

better pic(this one is declining for the season)

II’ll make sure to get better pics and may be even find some green or brown fabric that looks better..

Ken_Adrian I have plant lights in my basement. How many hours a day should i have them on? and thank you for your input. Donna

Just wanted to add that even if Mandevilla drops all leaves it is not dead. I stripped mine of all leaves due to persistent mealies hiding near the stem. And pruned to old thick brown stems. Wiped with 1:1 alcohol ev week for a month. and kept it in the sun warm in SO FL in winter (was around 70-75F during the day) and it regrew in a few months. But it was slow at first. So do not chuck it , keep it warm and sunny /under lighst and it will survive.

What you see on my pic above is growth from Mar to Aug this year from bare old stems.