My weekly פרשה lectures and הלכה column for the past פרשיות אחרי מות-קדושים discussed the Biblical prohibition against “walking in the ordinances” of the Gentiles. As I discuss, a debate over the scope and parameters of this prohibition is apparently behind the controversy over the custom (or family of customs) of the arraying of trees, grasses and flowers in synagogues and homes on Shavuos. I also recently published a detailed article focusing specifically on this custom, its history and its attendant controversy:
See also Flowers on Shavuos in Ami Magazine 2 Sivan, 5776 [June 8, 2016] pp. 66-70 and שטיחת עשבים ופרחים והעמדת אילנות בחג השבועות, in והנה רבקה יוצאת – עיונים במדע היהדות לכבוד רבקה דגן, pp. 211-17, both by my friend Eliezer Brodt, and Trees and Flowers on Shavuot: Is it a Pagan Practice or not? (audio) and Flowers and Trees in Shul on Shavuot in Torah To-Go, Shavuot 5777, both by my friend R. Ezra Schwartz.
In both parashiyos Acharei Mos (18:3) and Kedoshim (20:23), we are prohibited from “walking in the ordinances” of the non-Jews. This prohibition is the basis of a controversy over the custom of decorating synagogues and homes on Shavuos with grasses, trees, and flowers. The Maharil (Hilchos Shavuos) records that (fragrant) grasses and flowers (shoshanim) were arrayed on synagogue floors “for the joy of the holiday”. The Magen Avraham (siman 494 s.k. 4) records the placement of trees in synagogues and homes, which he suggests was intended as a reminder that on Shavuos we are judged regarding the fruits of the trees, and that we should pray for them.
The Gaon of Vilna reportedly opposed and abolished (at least locally) the custom of trees (and perhaps also that of grasses), since in contemporary times, the non-Jews have a similar custom on their holiday of “Pfingsten”, i.e., the Christian Pentecost, which occurs fifty days after Easter Sunday, thus paralleling, and occurring around the same time as, Shavuos, the Jewish Pentecost (Chayei Adam 131(130):13, Chochmas Adam 89:1, Aruch Ha’Shulchan OC 494:6, Shut. Igros Moshe YD 4:11:5).
But while a number of important halachic authorities, particularly within the “Lithuanian” / yeshivah tradition, follow the Gaon’s position, other major authorities reject it, in reliance upon the doctrine that non-Jewish practices are not forbidden as long as they have a rational, legitimate basis. R. Yosef Shaul Nathanson relates that he queried the non-Jews about their reason for the custom, and received a response from “their elder” that it was merely for the purpose of “honor and adornment with beautiful trees”. It therefore has a rational basis and is permitted (Divrei Shaul / Yosef Daas YD #348). R. Shalom Mordechai Schwadron justifies the custom based on the fact that we have a legitimate rationale for it, as a reminder of the judgment regarding the fruits of the trees (Orchos Chaim siman 548 os 8 – see there for an additional basis for leniency). [R. Asher Weiss notes that the Gaon is on record as rejecting the doctrine that the existence of a rational basis legitimizes non-Jewish customs (Biur Ha’Gra YD siman 178 s.k. 7), which explains his stringent position with regard to grasses and trees on Shavuos (Minchas Asher Vayikra 33:2).]
My lectures are available at the Internet Archive. Previous lectures I have given on this topic are also available there: here and here.