Is there an amount needed in order to fulfill the mitzvah of burning Asheirah trees? Is a blessing recited upon the burning of an Asheirah tree?
See Sefer Hachinuch mitzvah 436, who implies that the fulfillment of this mitzvah [destroying avodah zara] is fulfilled when the avodah zara is completely destroyed, burnt or broken, to the p0int that it is no longer recognizable as an avodah zara “שלא נניח רושם לעבודה זרה”.
Why there is no bracha on this mitzvah is a good question raised by a number of authorities. Some suggestions are: – since there is a bracha on seeing destroyed avoda zarah, no bracha was instituted on the actual destruction [Shoshanim L’Dovid]. – A bracha is to declare the oneness and power of Hashem in this world and that we are fulfilling His will. The act of destroying avodah zara itself accomplishes that and hence no bracha in necessary [Olas Shmuel – Kvider Siman 97].
In fact the Maharsha to Brachos 57b writes that in his opinion a bracha should be recited when destroying avodah ara in Eretz Yisrael!