I would go for shortening the fronds by half. The Junipers are definately starving the Tamarisk so a good feed and regular watering and trimming the Junipers away from stems will improve the situation.

Thanks ....by the fronds..do you mean the the branches.. or the feathery bits? and what feed would you advise ??

I meant the feathery bits at the end of the thicker branches. Feed with something like blood, fish and bone but as I said the Junipers will always restrict the growth of your Tamarisk. The ideal would be to cut back the Junipers and perhaps give the Tamarisk a mulch as a means of keeping the moisture around the roots.