I've got some planted in my small 45Ltr tank, it's been in there for about 3 weeks and is just starting to take off, I think this is a bit slow, but there ya go !
Originally I planted it in clumps, but this had limited success.
I was then advised to plant each individual 'plantlet'. If I'd done this I'd still be planting it !! But I think the advice was good, all that was lacking was my ability to spend a whole day planting each plantlet

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A set of tweesers (preferably long ones) is a great help and so is a large amount of patience. Pull up a chair and dont plan on doing this quickly !
What I did do was to plant it in much smaller clumps than I had originally ... as small as I could realistically manage. I had problems with it staying rooted in the substrate (Eco-complete), but finally it seems to be settling in, the tank is fairly new and I've had some problems with brown diatom's, however my Amano shrimp are cleaning it up nicely and it has started to fill out
I have quite a bit more HC to plant in the next few days ( a solid mat about 8" by 6"), as I've just had a delivery, the trouble is the tank it was destined for isn't ready for it yet .... so I have a bit of a rethink to do ! (yet again ! ). It's currently growing emersed in containers under a 20W light, but I want it planted soon.
Basically, I've had the most success with planting it in the smallest clumps you can mangage, with good lighting and added CO2.
Mr G