Straw (or, maybe intended, hay) was discussed as fungi-'fertiliser', like scrap paper can be.
If an aboveground cereal[1] stalk still has some seeds, then germination (and definitely full 'weed' growth) is probably curtailed in a fungi-growing circumstance. Although maybe malted grains could be beneficial to the mycobiological growing process.
The 'straw' used by strawberries (traditionally, IRL, and I think the recomendation is barley stalks) is partly there to help the fruit. In dry weather, helps the soil retain moisture, in wet it keeps the 'berries' (actually 'aggregate fruits' - bananas are berries, strawberries are not) from touching the soil. I'm not sure it has any significant fertilising action during growing season, nor do I recall Pick Your Own farms having any obvious "cereal weeds" when going up and down the rows. But that could have been due to off-season weeding. These days, they might use polythene or heavily processed (perhaps heat-treated) fibrous matting for the same purpose. (Although it's occured to me that I haven't seen a roadside PYO sign for
many a year, so changing markets and processing all over.)
Restricting/tuning crop-seasons for aboveground plants (I can't recall if fruit trees are annual-only, they certainly have things like seasonal leaf-colour changing, but I do too little deliberate orcharding) is probably more obvious than for the ones that shun the surface conditions completely (dig channeled 'room' into multi-layer soil and then cover it with a roof or even a tower and the soil grows fine surface crops despite everything[2] and never again anything subterranean, even if the chamber did before you let open the roof). - The only explanation I have for this is something like a seasonal 'pulse' of trace elements (like radon, perhaps, but more so) that leaches throug the rocks but entirely dissipates given any slight contact with aboveground breezes (should therefore not be possible under a deliberately maintained overhang, or where sufficient access aboveground lets the wind breeze in one tunnel entrance, through the complex and out another, and full-on Turtling up the exposed place should protect against draughts as much as even the more exotically elemental FBs; thus showing that my 'explanation' is already a dead duck.
)
Starting from scratch, I'm sure we could far more rationally reconstruct this fantasy ecosystem/agrieconomy. But some things would overturn much of the pre-existing Lore. I'm on tenterhooks to see what future changes might creep in, minor and major. Those that most satisfy the Realists might upset a lot of the Traditionalists, though.
[1] Not that of cave-wheat, because of whatever adaptation drives this as an underground crop. (In my head, it's just another fancy mushroom, anyway, that just has undergone convergent evolution into flour-grindable 'seed' heads/ears, rather than a cave-adapted 'grass'. But I probably have very little reason to justify that opinion.
[2] If this 'bug' functionality is ever fixed, I'm going to have a harder time with my own farming. Shouldn't complain, but likely will.