Thalia 'Dealbata'So tall! The Thalia (Thalia dealbata) can grow up to 1. 5 metres tall! The spear shaped leaves protrude high above the water with blooming spikes. For stunning ornamentation in our garden! Plant the Thalia in the spring. The plant flowers in the summer. We maintain a maximum planting depth of 40 cm. Just remove the older leaves in the spring. Put the Thalia somewhere in the sun.