Encourage Amazon sword to send out runners
 

Any suggestions on how to "encourage" amazon swords to send out
runners? I bought this sword with one runner. Shortly after
planting, about a year abo, it sent out another. I subsequently
removed and got 7 nice sword plants. Since, the main plant has grown
to 3-4 times its original size. IN a 55 gal and has leaves up to the
surface. But no more runners.

Suggestions?