When can you harvest it for salads?

JUST KIDDING!!

In 6 months or so, my water celery has stayed a smallish plant. I had
it in rocks in a pot and the roots grew out over the top into the
water. I repotted it in soil with gravel and rocks on top and the
roots, again, came out of the top in abundance. That's great that the
roots are so happy, but how do i get the leaves to grow?

Thanks.