The resource pack attached offers a complete fix for this issue. Mojang have my full permission to (and are encouraged to) replace the affected vanilla model files with the contents of the resource pack.

Download resource pack:

• 22w16b: nether-wart-raiser-22w16b-v1.0.zip

The bug

The planted nether wart block refers to the same "crop.json" model file as overworld crops such as wheat. While this is fine for the most part, in practice it results in some of the pixels of the nether wart texture being buried in the soul sand.

The crop model is offset one pixel downwards as to match the shape of farmland (MC-50155), which results in a seamless connection for other crops, but as soul sand is a full cube, the bottom layer of the nether wart texture ends up being completely hidden when it should be visible.

How to reproduce

1. Plant seeds on farmland
2. Plant nether wart on soul sand
3. Enter Spectator mode and fly inside the farmland and soul sand

Expected results

The wheat crops and nether wart should have all of their pixels visible from aboveground, and flying into the base blocks shouldn't reveal anything new that isn't normally visible.

Actual results

This is true of the wheat, but the bottom layer of nether wart's texture is completely obscured by the soul sand.

How to fix

I've attached a resource pack to this ticket which fixes this issue entirely, alongside fixing a few other issues. Mojang have my complete permission to use these assets in-game to fix this issue (and are strongly encouraged to use it due to it fixing other issues which would likely otherwise remain in the game for needlessly long and require more time to fix).

This resource pack introduces a new "hash" template model, which is identical to the crop model except that its planes range from 0 to 16 pixels on the Y axis, rather than the -1 to 15 for crops, such that the entire texture for nether wart is visible in all stages.

This resource pack also fixes some minor issues with seagrass, which I've made to use this model instead (thus deprecating template_seagrass.json). The hash model accepts two different textures (for blocks like nether wart which use only one texture, template_hash_all.json collapses the two textures into one parameter in much the same way as cube_all), and each seagrass texture has been split into two, with a new texture halfway offset.

With these two texture options and alternate seagrass textures, this resource pack contains a fix for MC-202598, which was resolved as Won't Fix due to its originally proposed fix resulting in seagrass swaying in two directions at once, which was considered aesthetically undesirable. This resource pack fixes MC-202598's mirroring issue while getting around the "plants not swaying in the same direction" issue at the same time, since the alternate texture sways in time with the original (and arguably feels even more natural as a result due to subtle differences in the texture).

In addition, this partially fixes MC-203406, since the hash model does not include any redundant tintindex parameters that go unused.

Hopefully this paragraph makes these bonus fixes clear enough.