You’ve probably always been told that you have to plant an amaryllis (Hippeastrum) leaving the top third of the bulb exposed. Thus many gardeners are convinced that this is absolutely required, that the plant will rot if ever it were to be covered completely. However, wild amaryllis bulbs grow completely underground, like most bulbs. Why the difference?
The idea that the bulb has to be planted with its neck exposed comes from the fact that the amaryllis is largely grown as an indoor bulb. The bulb is so large that, if you did bury it completely when you plant it in a standard pot, there would be no room for the roots. By planting the bulb with the top third of the bulb exposed, you’ll be leaving plenty of room for its roots to develop underneath. And indoors, with no predators out to eat any bulb part that is exposed, this unusual way of planting the bulb does no harm.
However, if ever you do plant your amaryllis bulb in an extra deep pot while leaving the neck exposed, you’ll discover it will actually pull itself underground over the next year or so, thanks to its contractile roots.
If you live in a mild climate where you can plant amaryllis bulbs in the outdoor garden (zones 9 to 12), you’ll find they do much better when the bulb is completely buried. Plant it in a rich, well-drained soil, just barely covering the bulb. Depending on the cultivar, it may stay at that depth or “dig itself deeper” over time.
Some gardeners even manage to grow amaryllis in zone 8 or 7b, but if so, plant the bulb more deeply, with up to 3 inches (8 cm) of soil covering it, and mulch it heavily in the autumn as well, as you’ll want to keep the bulb frost-free.
Amaryllis: the planting depth depends on root growth and cold protection. Who knew?