[magicmagni]

I would think trimming hairgrass would cause the cut blades to begin to die off and then new growth would take the place of the cut blades.

This has been my experience. Cutting does speed up the growth too IMO. Great for jump starting it and also for helping it grow in nice and thick.

 

[magicmagni]

The plant spreads via runners. Maybe every 1/8 inch will be a new blade of grass with a root. Each one of these becomes a new plant. I like to thin mine out with a coarse hair comb. Not only will this remove debris and algea/foreign plants, it will remove some of the baby plants that you can replant or toss. You can also define a border by plucking pulling out the little plants and cutting the runners around your perimeter. Some have even used plastic borders to contain the plant in one spot although I think thats overkill.

 

[magicmagni]

Yes it is a big pain because the nets dont have the mesh close enough so the grass slips through, picking by hand is harder.

Brine shrimp net;-)

Have a bucket on hand with some water close by to swish it around in to get the grass off or else it all sticks to the net and you can't get it off as easily.