Are we talking Dutch hyacinths (Hyacinthus orientalis) or grape hyacinth, Muscari species?

Dutch hyacinths are typically not divided. In fact, the bulbs' vigor and size tend to decline in subsequent years so these are often treated as annuals and replanted yearly. Grape hyacinths (muscari) naturalize readily and are often divided. This does help maintain bulb vigor as well as good spacing. Dividing is best done when the bulbs are dormant....like right now :-) Spring blooming bulbs start emerging from dormancy with root growth as soon as both air and soil temperatures start to cool.

Dutch Hyacinths, not Muscari... Oh well, I thought Hyacinths were naturalizing...

What is the Zone for Dutch Hyacinth? I'm Zone 4 or Zone 5A.

I've had Dutch Hyacinths growing for over 15 years...and they just keep on multiplying... Definitely dig them up now and replant/divide... In fact they may be the most dependable perennial bulb (other than Spanish bluebells and muscari...LOL) in my garden! They may do better in some areas of the continent than others...I'm in the PNW.