I let it grow as long as it will without going out the top, even if I have to add something to hold it down. Once it comes out of the water, it tends to dry too much. But if I give it time, it will start putting out roots at spots along it and when those roots grow long and sturdy enough. I bob them off the main plant, leaving an inch or so at the new roots and plant those in new spaces. Pretty much like taking clipping from garden plants except these have the advantage of already having roots which does make it much more likely to succeed. Once it has good roots, it does not need the old stem but can do it's own thing.