I normally give some microelements mixed with the repotting soil and
sometimes I sprinkle some this period of the year on the surface but when is
the best period and how often shouldl micro elements be given to the bonsai?


Why would you give fertilizer at this time of year, except to indoor bonsai?
Many fertilizers nowadays contain trace elements, including Miracid, Dyna-Gro,
& some of Peters. Your best bet is to rotate among several different brands, &
make sure you give a fertilizer with trace elements about once a month during
the growing season. I don't bother with those organic cakes or other
concoctions, but I found the plants seem to like fish fertilizer and seaweed
extract. I feed Neptune's Harvest about once a month. Just watch out for
yellowjackets when you use it outdoors.
Iris,
Central NY, Zone 5a, Sunset Zone 40
"When you come to a fork in the road, take it." Yogi Berra