Hi Proton-wira,
Concerning about your boxwood, firstly I would like to say is I don't know much about the climate up there in your region.
All I can tell you about boxwood is growing in the hot wet climate in my country only.
Boxwood is a fiber root plant and grow well in loose soil with higher humus content but not water logged. During the dry season it got to be well watered.
I found that it grows better in a shallow wide pot rather than in deep big pot. Boxwood is absolutely an outdoor plant but can't be exposed to the hot blazing sun full day.
My boxwood are placed in between 2 palm trees and the hot afternoon sun is sheltered off. They only expose to the morning and evening sunshine.
As for application of fertilizer, I use urea-N46. dissolving 2 table spoon full of the N46 in 3 liter of water and apply once every 2 weeks. urea N46 give extra nitrogen
to all the plants and make the foliage greener, look fresh and healthy.
By looking at the photos of your boxwood, I suggest you look into the roots of your plant. As boxwood is fiber root plant, it can get root diseases easily. If so, you will
have to re pot and change all the soil. Or ... could it be over application of fertilizer? On the whole, I suggest you re pot your boxwood but try not to cut away much of their roots.
unless they are infested, and cut away all the dry branches and let them grow again.
Good luck to Buxus harlandii !