So, I decided to harvest a full-grown horseradish leaf with chlorosis, today, and eat it. This is the first horseradish leaf of my my plants that I've eaten. The soil had loads of wood ash in it (so it probably needed more nitrogen and less calcium or something). The plant is getting green now, however.
Recap: Earlier this year, in the spring, I tried a friend's horseradish leaves, and they tasted like strong cabbage. The texture was kind of chewy, and the skin was thin and maybe a little stretchy. It tasted like powerful cabbage, except the stem tasted like horseradish. The only fibrous part was the stem below the leaf.
My leaf today was quite different. The whole leaf tasted kind of like horseradish. It reminded me of hot radishes, except it wasn't fibrous (except for the stem and some inches of the center vein). It had a great texture for fresh-eating (not tough or stretchy). It did have some sinus-clearing properties. It left a smell in my mouth as if I had just eaten a good sandwich. It felt healthy. So, I ate some more of it (the spiciness made this a slow process), and then I put the rest on a sandwich and ate it. The sandwich definitely masked most of the spiciness, and made eating the rest of the leaf quick work. It was good on the sandwich (which was just bread, cheese, and the leaf).
I'm not sure if my horseradish is the same sort as the kind I tried earlier in the year. The kind I ate today had western shade, and probably some southern shade, and it had black plastic around it. The other kind was in full sun, with no black plastic; it also had no chlorosis.