Hard pruning a tamarix

I have a 9 year old tamarix that, I suspect, has a weeping gene/mutation - no matter what pruning I do, it has a strong downward sloping, low, wide habit.  It's less than 4ft tall over most of the plant but a good 15ft across now.

It's very pretty and I like it, but it's planted in my lawn which makes mowing up to it very difficult and in places impossible, as some of the branches are runing just above ground level.

I want to put a flowebed in round it to save the mowing and add some colour contrast with low-growing plants, but to do so, I'll need to take it back almost to the ground - just a few feet across at most, less in places so I can get the grass removed up the base.

Will it cope with a prune that hard and would I be right to do it now, as it's finished flowering?  Or when would be best?  Any other tips to help it recover?