What's the deal with horseradish at the seder?

Question

Every Pesach seder I've been to, including ones run by Chabad and Hillel, has used horseradish root as the maror. But this seems to be controversial -- maybe horseradish isn't ok at all, or maybe horseradish leaves are but not the root.

This comment cites the Mishna B'rura (473:42) as allowing. Other comments there say:

If you mean ample late authorities, then yes that is the case. You will be hard pressed to find rishonim who say so, and any who do are likely referring to the horseradish leaf, not root, as the Mishna seems to explicitly exclude the root. See for instance, Haghot Maymoniot 8:13 who notes horseradish as the translation and then immediately says that roots are no good. – Double AA♦ Mar 18 '13 at 5:30

@DoubleAA Yes, I was referring to acharonim mostly. | The Hagahos Maimoniyos (7:13) mentions horseradish ("meerrettich"), as you pointed out. He then goes on to cite Rabbeinu Tam, who I initially interpreted as inferring that the species of maror mentioned in the mishna can only be eaten moist if their roots are eaten, whereas their stalks can be eaten moist or dried out. At least that's what I think Rabbeinu Tam might have been saying based on the context of the gemara, though I didn't see the direct quote. The Shulchan Aruch, though, says explicitly that roots are no good.... – Fred Mar 18 '13 at 6:58

I also read somewhere that horseradish is dubious but has such a long tradition for Ashkenazim to be valid for that community.

So, what's the deal with horseradish? Who permits it, and are there any conditions? Who forbids it outright? It looks like I could assemble a partial answer from these comments, but I'd rather have a complete answer in one place, hence this question.

Answer 1

TLDR: The Talmud's preferred plant for Maror is lettuce-like and leafy. In cold climates people started using horseradish root because it was still too cold to grow leafy plants at Pesach time, and if you put together the right combination of opinions you can construct an argument that horseradish root fulfills the Mitzva. The argument isn't particularly convincing nor does it represent the majority of classical opinions.

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The Mishna (Pesachim 2:6) lists 5 plants to use for Maror, and allows using their stems (using the leaves didn't even need to be specified). As with all species names, translating them is notoriously difficult. The first species, חזרת, is the ideal one according to the Gemara and it is some kind of lettuce. The third species, תמכא, according to most early Rishonim (such as Rashi, Arukh, and Rambam) is not horseradish. However, some later Rishonim (eg. Haghot Maymoniot, Agur) translate it as horseradish. These Rishonim all do not allow use of the root of a plant (and so is ruled in Shulchan Arukh OC 473:5), only the stem or leaves (in the words of Maharil "what grows above the ground"). (Indeed here is an old Haggadah that discusses using horseradish leaves.) Eventually Magen Avraham (17th century Poland) argued that large taproots should be considered as stems, not roots, and be acceptable for use. As noted elsewhere, horseradish taproot is barely considered edible and it presents certain bracha challenges at the Seder.

So, in order to get at horseradish root being Kosher, we need to accept the translation of תמכא as horseradish, accept that taproot are stems, and accept that raw horseradish is edible. Then you still have to force yourself to eat an olive's bulk of it, figure out what blessings to say when, and figure out how to dip it in and shake off the Charoset. And even then you won't have fulfilled the Mitzva in the best way since ideally you should use the first species listed which is חזרת. But add in a minority opinion that any bitter plant qualifies even if not on the list (see Rama 473:5), and if that's all you've got, then why not go for it? Indeed in many places (mostly northern Ashkenazi places) that's what they did.

Nowadays thanks to refrigeration there is lettuce readily available in most places. Do as your ancestors have always done and prefer that when it's available. ("חזרת is preferable to תמכא... but in our lands we have to use תמכא since חזרת isn't available before Pesach" -- Arukh haShulchan 473:13 about 120 years ago.)

(Note the prohibition against eating bugs is not pushed aside by the obligation of eating Maror, so don't be extra lenient in checking the lettuce for bugs. But unless you never eat lettuce all year, you should be able to arrange to have lettuce the one time it's actually a Mitzva. Note the white ribs of romaine lettuce leaves are generally easier to check/clean than the thin green parts, and also are more voluminous.)

Check out this article by R. Ari Zivotofsky for many sources on the topic.