Are you sure you have that name right? I am not familiar with any nandina of that cultivar name but 'Firepower' is a very popular variety.

I sometimes wonder why it is so popular as I find it to be the least desirable of any nandina cultivar. It has a much larger leaf structure so loses any of that lacy foliage effect of other nandinas. And with kind of a dumpy, lumpy growth habit compared to other cultivars. It is also overly prone to leaf spot and powdery mildew. And is not really a dwarf but more of midsized cultivar (can get as much as 60" tall). But it is sterile and can get pretty intense winter color, which likely accounts for much of its popularity. Unfortunately its propensity for leaf spot in my climate takes away from much of its winter appeal.

Pruning nandinas should be done from the bottom up, not from the top down :-) Top pruning or shearing a nandina seldom results in a pleasing appearance and sheared plants develop an awkward, unnatural growth habit. Generally, the recommendation is to remove any leggy or older canes at the base. This will encourage new cane formation from the base of the plant. And with the taller, more leggy varieties, pruning some of the exterior canes back by 1/3 to 1/2 can encourage foliage development that will fill in and hide the bare interior stems.

'Firepower' is not known for being a very leggy selection and seldom requires any pruning at all. But I can see where the much broader leaves than typical for nandina could make a mature plant somewhat top heavy with new growth and rain. Thinning would be your best approach in this case, rather than just whacking the plant back.

@gardengal48. Thanks, Firepower is the correct name. I usually remember the "fire" part & forget the rest. These were "lemonade" shrubs -- here, healthy, & free, so I made the most of what I had. These seem resistant to leaf spot in my zone 7a and do add a nice pop of color for winter. They will drop some leaves because we have 2 weeks or so of winter weather in the 10s & 20s that they don't like. So far all efforts to tidy up the neglected borders (dividing liriope & daylily, digging dead shrubs, strategically purchasing replacements ) seems to be going well. My best save was the pitiful Hydrangea that I had to cut down to the ground. It came back healthy w/ big beautiful blue flowers that keep coming until the first hard frost.

Actually, Fire Power does get leggy. It is not a cultivar made for taller growing. When it gets leggy, it flops over,....or just looks bad. Fire Power actually responds well to 'topping off'. I cut it about 4 to 6 inches above the ground in early spring and by Fall, it has filled in nicely and will stay low for a few more years, when you'll need to do it again.

There are taller growing cultivars if that is what you are after.