Does Planar Binding require you to keep concentrating on the summoning spell?

Question

Planar binding states:

With this spell, you attempt to bind a celestial, an elemental, a fey, or a fiend to your service. The creature must be within range for the entire casting of the spell. [...] At the completion of the casting, the target must make a Charisma saving throw. On a failed save, it is bound to serve you for the duration. If the creature was summoned or created by another spell, that spell's duration is extended to match the duration of this spell.

Most summoning spells require concentration. Would the original caster be required to continue concentrating on that spell even when planar binding extends the duration?

I was inclined to say "yes" to this, but it was pointed out that upcasting planar binding extends its duration to as much as a year and a day.

At Higher Levels. When you cast this spell using a spell slot of a higher level, the duration increases to 10 days with a 6th-level slot, to 30 days with a 7th- level slot, to 180 days with an 8th-level slot, and to a year and a day with a 9th-level spell slot.

It seems really unreasonable to expect concentration to be even over these extreme lengths of time.

Am I missing something here?

So, does planar binding require the original caster to maintain concentration on the extended summoning spell when one is present?

Answer 1

No

Planar Binding states:

If the creature was summoned or created by another spell, that spell's duration is extended to match the duration of this spell.

The duration of Planar Binding is 24 hours (or more if upcast), so the summoning spell's duration is changed to duration of Planar Binding. This means that it is not changed to Concentration (up to 24 hours), but rather just 24 hours, no concentration required.

If the summoning spell had a concentration time of greater than 24 hours, I might rule that the duration wouldn't change since it is not extending it, but that is an edge case that seem ambiguous to me.

Credit to Gandalfmeansme for catching this.

Answer 2

Yes, you still need concentration

Planar Binding says that

If the creature was summoned or created by another spell, that spell's duration is extended to match the duration of this spell.

Note that the spell duration is extended, not replaced or changed.

Hence, if the duration of the summoning spell was Concentration, up to one hour, Planar Binding would extend it to Concentration, up to 24 hours.

Answer 3

Also, wouldn't you lose concentration on a long rest? It wouldn't make sense to have the planar binding require concentration then, because it wouldn't last for longer than you would be able to stay awake or avoid a long rest.

And the argument that the planar binding’s duration replaces the previous spells also makes sense and the planar binding spell doesn't require concentration for its duration. The first spell’s duration and maintenance is replaced by the second one’s.