How to grow Summer Bulbs
Summer-flowering bulbs need sufficient water and humid conditions.
Summer-flowering bulbs should be planted when the soil temperature is approximately 13°C or 55°F, if planted before this temperature is reached, the bulbs will not begin active growth, which can easily cause the bulb to rot.
Summer-flowering bulbs are generally planted close to the surface (3-5cm or 1-2 inches deep), where the soil is warmer. Most summer-flowering bulbs, such as dahlias and begonias, should be harvested before the first night frost (depending on the climate zone).
If the winters are not severe you can perennialize the bulbs by leaving them in the ground and cover them for the light frost. Very often these bulbs will bloom better the following year.