Whenever you like. I recently planted a pot of spent hyacinths myself. Just leave all the foliage in place until it dies back on its own

Every Hyacinth in my garden started life as an indoor plant. Plant them immediately wherever you want hyacinths next spring. Don't wait. The bulbs need to build up their reserves and to do that they need to be in the ground.

put a stick or a rock to mark the spot.. so you dont dig them up after the leaves die to the ground in a few weeks..

cant tell you how many i dug up in fall.. planting mums or some such.. lol .. [or all the new spring flowering bulbs which are usually planted in october or so ...]

proper planting depth is generally 3 times the width of the bulb.. which might be a bit deeper than they were planted in the pot... this was done.. because they considered them disposable.. but there is a proper depth ...

these should be about a 2 inch bulb.. so 6 inches deep would do the trick ...

ken

I was recently given a coupla dozen hyacinths left over from the local council planting. Suspect they had been forgotten in the back of a shed. I stuck them in the ground (this was at the end of March - they were showing a good inch of growth) and they raced into bloom within 2 weeks. Bulbs are remarkably efficient storage systems and can often remain viable for many months.