South Florida zone 10b.

I have planted some Costus (Ginger family) in a 50' long planter area.
However the weeds are growing like wild fire and I am unable to keep up with
pulling them. I wanted to use some weed killer to control the weeds (clover
leaf type, see a pic here
http://www.biology-blog.com/images/b...-leaf-3100.jpg ), but
have heard that weed killer will also kill plants that have rhizones which
my Costus is.

Is this true? Is there a better way to control the weeds beside hand
pulling?

Thanks,

MC