I know a lemon seedling grows really big but I want to keep it smaller for my small room. I was thinking if a cutting from the original tree won’t grow as tall as my original tree.

I assume you meant you rooted a cutting off the top (of a now bearing tree) not grew a lemon and planting another seedling from it. Taking and rooting a cutting off the top will take time for it to establish itself, and liklely bear sooner than a ten footer that must have taken you some time (years?), but there's no reason to expect it not to eventually get as big as the 10 foot seedling. Its up to you to root prune

I'm confused. Did you grow a 10' lemon tree from seed? Are you getting fruit? Lemon trees are normally grafted. Lemons grown from seed and may take forever to fruit (internet seems to think 5-10+ years). Also, if it was a Meyer lemon seed or another variety that is not true to seed, when/if it does fruit, you will get some mutant citrus.

As to your question, most citrus can be pruned to whatever size or shape you want. If you care about getting fruit, I would not start over, instead I would try cutting the big tree to the size you want and keep cutting it back. If you do start over with your new tree, you will need to prune aggressively/regularly or it will get large like its parent.

If you continuously prune it, you will not get fruit.

What I meant was. I’ve rooted a cutting that I cut off from the top of my 3-year-old lemon tree grown from seed (still young to bear fruit). And I’m planning to get rid of my tall tree and keep the rooted one as I don’t have enough space to keep them both in my tiny room. I‘m not gonna deny that I want to see it bear fruit.

The cutting is growing healthy and now producing branches.

It should fruit soon.

Steve

No it won't fruit soon unless soon is 7 years.

Seriously, if you care about fruit and you can spare $15-$40, go buy a lemon tree. My Home Depot has little Meyer lemon trees for $15-25. You will get great quality fruit in 1-3 years and it is on dwarfing rootstock that will keep the tree small. Don't waste money on soil, fertilizer, etc for a tree that will grow too tall and may take a decade to fruit and may produce mutant fruit.

If its not bearing , yes you picked up node count with that cutting but why bother

Your growing cutting is 10 feet closer to fruiting than the original tree. It should do well with out the graft/sucker problems of a grafted tree

First of all, where do you live? And where are putting your lemon tree in summer (warm season)? Is it getting enough light? Your old lemon MAY fruit next season, or it may take years yet. Or it may never bloom. No one can tell you the answer definitively. But whatever you do, don't trim your old lemon tree because it needs to get a certain size before it can bloom....probably somewhere between 5 and 10 feet tall. Keep in mind plants tend to stretch out more indoors, so that magical node count may bring it up to 14 feet high or more.

If you must throw out your tall lemon, it was a good idea to root the top of it. That rooted cutting will still take some time to grow, and it may bloom eventually -- and at a smaller size than your original tree. That said, it can still get big, but once it blooms regularly, you may start to trim it back to a manageable size.

I live in Jersey and summer here gets hot. But I live in a house with no front or backyard. So, I can‘t leave my plants outside. It only gets 5 hours of direct sun from the window.