We should take much care of planting a H. mandonii. The main soil requirement is excellent drainage. And it is not good to give too much fertilizer.
I gave almost the same quantity of fertilizer to many species of native Hippeastrum plants. But only this species bulb split as the picture. If the temperature is too high in summer, bacteria attack the splitting part and then cause rot. Finally some insects grow and eat the rotting part. The situation becomes worse and worse.
Therefor there are some points in planting this species
a.Keep the soil dry
b.Do not give too much fertilizer
c.Put the pot in cool place in summer
When you find that the bulb stops growing in growth period or something abnormal for leaves, for example, some leaves dry up or hang down, it means something happens. You should dig the bulb out and check if it is OK. I saw these symptoms for some days but I am busy and do not check the bulb. Finally the situation gets worse.
I am trying to save it. Maybe I should do notch breeding.