In North America, we tend to bury the bulbs so
they don’t heave up. If there is at least 1.5” (3.5
cm) of mix on top of the bulb, heaving usually
does not occur. Again, the issue is sufficient
weight of mix on top of the bulb. It seems likely
that other treatments that would reduce the initial
vigorous root growth of (especially) hyacinths (for
example, reducing temperature by a few degrees
weeks 2-3 after planting) might help to slow initial
root extension and reduce lifting, but we have not
tested this idea.