What is commonly known as "Black Current Trimming" by gardeners, works nice.
You regularly cut about 1/3 of plantmass in the group, (fx when reaching surface). Choose the oldest (and longest) shoots and cut quite close to ground, letting light and flow into the group of plants, promoting new growth. This way the group looks "presentable" at all times, and plantmass is kept young and in growth. If possible, cut right above a leaf, this looks better in final presentation. I'd advise, to - at least now and then - replant some of the off-cuts, since these were the best growers, and constantly removing those, might end up rewarding the slower growers that are left. When replanting offcuts it's allways best to remove leaves, that would be covered in soil/substrate.
- And as usual ; Offcuts not needed can be pasded on to others..........
Mick.