They are definitely growing, although if they will actually produce fruit or not, I'll have to wait around 7 years to see. In the mean time, its a fun project.

I was wondering a few things:

How do I know if the tree is strong enough for pruning (I'll be growing it inside for around 4 years, so I'll need to try to keep it small)?

Has anyone else tried this before? Did the tree produce fruit?

I don't water it frequently, maybe only a couple times every two weeks, but the soil stays somewhat moist, so I feel like I don't need to. How often should I water these seedlings (approximately)?

Thanks for any help!

Secondly, no one can tell you how often to water your plant, not even approximately. That depends upon a whole slew of factors including: temperature of the environment, relative humidity of the environment, type of potting medium, type of container, size of the container in relation to the size of the plant/root system, amount of light, time of year, etc. You'll have to learn by 'touch'.

I tried and tried to grow lychee (in containers) when I was in coastal SC, zone 8b. I could leave mine outside but for the coldest of temperatures. They can take below freezing temps as long as the containers (roots) are protected, but they simply did not like being grown in pots.

Should you be lucky enough to grow your lychee to the point of flowering, you'll probably have to aid in pollination. Bees and other pollinators will be happy to assist, but with just two plant, you might need to devote a bit of time to the task.

I LOVE lychees, so I wish you all good luck.

Unfortunately since I'm in an apartment, I don't have the most ideal growing environment for them. They get around 5 hours of direct sunlight, starting with morning sun, but that's about it. If they survive this year, I may be somewhere next year that I can put them outside during the summer at least.