I started a Japanese Maple from seed three weeks ago and Id like to know when is the best moment to repot it.

a picture of how's now

Are you sure of the species? it is an odd looking maple leaf. As for repotting all you need to do is pot on to a larger pot that way you will not disturb the roots. But in that pot it can stay for months. If it as it looks to be inside then get it out it is already getting very leggy from lack of light

I don't think that's a japanese maple.
As for repotting, I would wait untill next spring, wait for it to get some vigour, and when the buds start to emerge in early spring (assuming that's a deciduous), repot it and cut the long straight root that generally emerges from seeds.
Cheers!

it is from a starter kit. i hope its a maple

afherreraphoto wrote:

it is from a starter kit. i hope its a maple

It doesn't look like a maple, but it could be the cultivar.

If it's a maple, I wonder if it could be an Acer Platanoides. I am fairly sure it is not a Japanese maple.

If you want real Japanese maple seed, do not buy these kits, buy seed from a reputable tree seed seller.