The following question arises frequently nowadays: what should a married couple do when one spouse comes from a family that refrains from kitniyot and the other from a family that eats kitniyot? A similar matter was addressed by one of the great Rishonim, R. Shimon b. Tzemaĥ Duran (Tashbetz 3:179), who writes that they obviously cannot eat together at the same table while food permissible to one is forbidden to the other. Therefore, the wife must adopt her husband’s customs, for “a man’s wife is like his own body.” If the husband dies, it depends: if she has a child from him, she keeps his custom; otherwise, she reverts to her family’s custom.
R. Moshe Feinstein (Igrot Moshe OĤ 1:158) adds that the wife’s status is similar to that of one who moves to a place where the accepted custom is different from his own. If he intends to settle there, he relinquishes his previous custom and accepts the custom of his new home (based on SA YD 214:2, OĤ 468:4, and MB 14 ad loc.). When a woman marries, it is as if she moves permanently into her husband’s house, and she must therefore adopt his customs.
Accordingly, if an Ashkenazic woman marries a Sephardic man, she may eat kitniyot during Pesaĥ and need not perform hatarat nedarim (annulment of vows) because she is acting in accordance with the law that a woman adopts the customs of her husband. Nevertheless, some poskim recommend that she perform hatarat nedarim.
. Igrot Moshe OĤ 1:158 proves that this is a Torah law from the fact that the Torah exempts a married woman from the obligation to honor her parents, since this mitzva would require her to actively clothe and feed her parents if necessary, and her obligations to her household take priority (SA YD 240:17; obviously if there is no clash between the two obligations, she is commanded to honor her parents). Thus, according to the Torah, a woman’s place is in her husband’s home.
Igrot Moshe also asserts that she need not perform hatarat nedarim. MB 468:14 states that one who moves from one locale to another must behave according to the custom of the new place. It is implied that since this is the halakha, there is no need for hatarat nedarim. This is also the opinion of Kaf Ha-ĥayim 468:43. Additionally, in extenuating circumstances even Ashkenazic communities did not accept the custom of refraining from kitniyot and can therefore be lenient in situations of famine or sickness (MB 453:7). Similarly, two different customs in one household would certainly cause tension, and thus she changes her custom without performing hatarat nedarim. Sidur Pesaĥ Ke-hilkhato 16:13 states that she must perform hatarat nedarim, and Ĥazon Ovadia (p. 56 and n. 10) states that it is better to perform hatarat nedarim.
May Ashkenazim perform hatarat nedarim and eat kitniyot? Kaf Ha-ĥayim 453:15 states that according to Mahari Levi (§38), one who refrained from eating kitniyot because he thought they are ĥametz may perform hatarat nedarim, but one who knew, or whose ancestors knew, that kitniyot is merely a stringent custom may not perform hatarat nedarim. Thus, Ashkenazim may not perform hatarat nedarim and eat kitniyot. According to Pri Ĥadash §468, one need not perform hatarat nedarim to annul a custom that originated in a mistake, so even one who knew that kitniyot is just a stringent custom may annul his vow and eat kitniyot. However, we need to examine whether he would apply this reasoning to a custom accepted by an entire community; perhaps even according to Pri Ĥadash hatarat nedarim would not be effective in such a case. Ĥatam Sofer OĤ §122 upholds the opinion of Mahari Levi. This is in fact the customary practice: we find that Ashkenazim do not perform hatarat nedarim and eat kitniyot except in the case of a sick person. Sidur Pesaĥ Ke-hilkhato 16 n. 47 and in the addenda quotes some who believe that kitniyot originated as an enactment (“gezeira”). According to this, even an Ashkenazic woman who marries a Sephardic man would not be permitted to eat kitniyot. Nevertheless, we do not follow this opinion, and an Ashkenazic woman should follow her husband’s customs.