1) If a garment of four corners is covered in another garment (like a quilt cover), on which garment should the tzitzis be put?
2) Is a blanket of four corners (that one sleeps in during the day) obligated in tzitzis?
Answer:
Tzitzis are hung on the four corners of a four-cornered garment, even if it is covered (usually we wear our tzitzis under our clothes, and this is not a relevant factor in the obligation or the placement of the tzitzis strings).
The Shulchan Aruch (18:2) rules that one does not place tzitzis strings on a quilt or sheet, the Darkei Moshe (4) explains that this is not derech malbush (one does not “wear” a quilt).
However, the Vilna Gaon (5) writes that this ruling follows the opinion of the Rosh, whereby a kesus lailah (night garment) is exempt from tzitzis even when worn during the day, and according to the Rambam, there is an obligation to hang tzitzis on a quilt when using it during the day. This is likewise mentioned by the Beis Yosef (in the name of Hagaos Maimonios), who writes that the universal custom is nonetheless to see a quilt as exempt from tzitzis.
Because the issue remains unresolved, the Magen Avraham (3, also quoted by the Mishnah Berurah) writes that one should preferably round one of the four corners of the quilt, thereby ensuring that there is no obligation of tzitzis. However, he limits this ruling to a woolen quilt, where the potential obligation is a Torah mitzvah. See also Peri Megadim.
