Spiritual Gardener is someone who first of all cultivates the garden of his own heart. He plants the right seeds, waters them nicely, and also takes out all the unwanted weeds.
He also helps others to do the same.
Srila Prabhupada writes in the Srimad-Bhagavatam Purport:
The conditional changes of the living entity are explained in the Caitanya-caritamrta in the instructions given to Srila Rupa Gosvami by Lord Sri Caitanya:
“The living entities all over the universes are enjoying the effects of the respective fruitive results of their own work, life after life.
Out of all of them, some may be influenced by the association of pure devotees and thus get the chance to execute devotional service by attainment of taste.
This taste is the seed of devotional service, and one who is fortunate enough to have received such a seed is advised to sow it in the core of his heart.
As one cultivates a seed by pouring water to fructify it, the seed of devotional service sown in the heart of the devotee may be cultured by pouring water in the form of hearing and chanting of the holy name and pastimes of the Lord.
The creeper of devotional service, so nourished, gradually grows, and the devotee, acting as a gardener, goes on pouring the water of constant hearing and chanting.
The creeper of devotional service gradually grows so high that it passes through the entire material universe and enters into the spiritual sky, growing still higher and higher until it reaches the planet Goloka Vrndavana. The devotee-gardener is in touch with the abode of the Lord even from the material plane by dint of performing devotional service to the Lord simply by hearing and chanting.
As a creeper takes shelter of another, stronger tree, similarly the creeper of devotional service, nourished by the devotee, takes shelter of the lotus feet of the Lord and thus becomes fixed.
When the creeper is fixed, then the fruit of the creeper comes into existence, and the gardener who nourished it is able to enjoy this fruit of love, and his life becomes successful.” (SB 3.2.6 Purport)