Filling in with mixed greenery is actually pretty quick and easy to do. I'm going to use leather leaf fern to begin. I always recommend that you order at least a few bunches of this versatile green. It's cheap, looks nice and fills in quickly.
The individual laterals can be cut apart with an knife and inserted cleanly into the florist foam.
Here I inserted my first piece of leather leaf fern.
Cut off the separate laterals and insert at an upward angle. Point the fern downward so the tips lightly brush the table top.
Work your way around the entire arrangement.
Now work upward, beginning to angle the piece up and out, until the top pieces stick straight up.
Just one or two stems of leather fills in a design like this one very quickly. Don't overpower your lily grass work - you want it to stand out a bit and above the other. I then mixed in some other greens, including boxwood and variegated greenery.