Plant Growth is so useful
And i'm not even talking about the "fertilizer" use, which could be a serious way to curry favor towards a community or a king etc.
The instant version overgrows a 100-foot radius of plants, which is huge, but you can also exclude one or more parts of the zone from becoming overgrown. Need to slow an incoming foot army ? Need to prevent attackers from escaping you ? Need to provide some flammable material or wood to prepare better for a siege or whatever ? I know it's 3rd level but really i love this spell so much.
My Archfey Warlock just made good use of this spell when we were protecting a city from a siege. Kobolds started climbing the cliff atop which the city lies, and i used plant growth the slow their progression, allowing the guards and our martials to skewer them on arrows, and our draconic sorcerer to burn them better now that they were hindered by the overgrown vegetation. Maybe it's because i cast all my spells at highest level, but yeah i love this one.