The description of hail of thorns (1 minute duration, 1 bonus action casting time) says:
The next time you hit a creature with a ranged weapon attack before the spell ends, this spell creates a rain of thorns that sprouts from your ranged weapon or ammunition. In addition to the normal effect of the attack, the target of the attack and each creature within 5 feet of it must make a Dexterity saving throw. A creature takes 1d10 piercing damage on a failed save, or half as much damage on a successful one.
The description of conjure volley (instantaneous duration, 1 action casting time) says:
You fire a piece of nonmagical ammunition from a ranged weapon or throw a nonmagical weapon into the air and choose a point within range. Hundreds of duplicates of the ammunition or weapon fall in a volley from above and then disappear. Each creature in a 40-foot-radius. 20-foot-high cylinder centered on that point must make a Dexterity saving throw. A creature takes 8d8 damage on a failed save, or half as much damage on a successful one. The damage type is the same as that of the ammunition or weapon.
Is it possible to have a combo with conjure volley and hail of thorns, even if it takes two turns to set it up?
For instance, I spend my first turn to cast hail of thorns, then use my action to stealth or something. Then, on my next turn, I cast conjure volley, which duplicates the arrow I cast hail of thorns on. The arrow isn't magical, so this should apply. I fire at a group of creatures. This should cause a hit even if the creature makes a successful saving throw.
Would this combo work?
Would I be able to combine conjure volley and ensnaring strike in a similar way?
Best Answer
No, this would not work; conjure volley isn't an attack
Hail of thorns specifies that its effects apply
However, conjure volley does not involve a ranged weapon attack. As part of the spell, you do "fire a piece of nonmagical ammunition from a ranged weapon", but that is simply part of what triggers the spell; you are not making a ranged weapon attack against any target. Instead, conjure volley is a spell that forces those in the cylindrical area of effect to make a Dexterity saving throw.
Ensnaring strike wouldn't work with conjure volley for the same reason: conjure volley isn't a weapon attack (or an attack at all).
For a definition of what constitutes an "attack" (and why a spell that only involves the targets making saving throws isn't one), see the "Making an Attack" section of the basic rules: