It seems Growthcraft crops are unaffected by the Drum of the Wild. Is there anything you can do about this, or would this have to be something the dev of that mod would have to do?

Although it could be done on Botania's end, it is much better for it to be done by the Growthcraft developer. If you want to contact Gwafu yourself, send him this link: https://github.com/Vazkii/Botania/blob/master/src/main/java/vazkii/botania/common/item/ItemGrassHorn.java#L128

Sent, but, I'll leave this up, incase there is anything that can be done on this side.

Just a heads up, that was probably intentional on the part of the Growthcraft dev to not allow his crops to follow normal plant rules.

I'm sure it is, considering how the crops are so radically different from most crops, but, I'm still making sure to see if there is anything Vazkii can do on her side.