Quickbeam is concerned about the large engines of war that the uruks possess. The enormous bolts they throw could seriously injure even an Ent.
'Though I dare not reveal myself yet, these little uruks are not much of a threat to me, even if their axes do sting a bit... but they have constructed engines that can hurl great bolts, often set aflame. These things could seriously harm even an Ent.
'There are ways to deal with such things, however. Take these seeds -- they have been bathed in one of my Ent-draughts -- and bury them beneath each of their engines. They will not threaten us much longer.'
The ballistae can be found in the uruk-encampment of eastern Nan Curunír.
Quickbeam asked you to plant seeds beneath the ballistae protecting the uruk-encampment.
Quickbeam is at his home upon the north-eastern slopes of Nan Curunír.
You should let Quickbeam know that the seeds have overgrown the uruks' siege-engines.