Mantra seeking blessings of Kalpa Vriksha

Is initiation necessary to listen to this mantra?

No. Initiation is required only if you want to do mantra sadhana, not for listening. You just have to listen to the mantras we provide to get benefited.

नमस्ते कलपवृक्षाय चिन्तितार्थप्रदाय च ।
विश्वम्भराय देवाय नमस्ते विश्वमूर्तये ॥

namaste kalapa vri'kshaaya chintitaarthapradaaya cha .
vishvambharaaya devaaya namaste vishvamoortaye ..

Salutations to Kalpavriksha, the fulfiller of desires,
To the sustainer of the universe, the divine form,
Salutations to the one embodying the cosmos.

Ramaswamy Sastry and Vighnesh Ghanapaathi