I think that hafen lacks rly much more decorative items. Decorations doesnt need any mechanics, so should be easy to implement.
First thing that is in my mind are flower beds. We have just flax, and poppy flowers to be planted on ground and this could be a makeshift of flower bed, but its usualy not good looking.
Here is one cool flower bed made of log:
It could be even lifted. You should first prepare a log (like you make runestones of stones), then it works similar to garden pot. You fill it with soil and then place any kind of flower type plant (or add possibility to change its color with dyes?). Its however not possible to harvest it, so can't be used to grow plants. Purely cosmetic thing.
Another one would be made of boards:
Another thing- statues. Made of stone, or even bronze?
Maybe some hedges? Placed piece by piece like trellis (which are actually used as better looking garden fences ) so people could make pretty nice garden designs:
Maybe even shears for bushes, to make them look like specific shapes?
Regards, and hugs to all hafen gardeners