Possible Clues:

• Underground stem producing roots and leafy shoots
• Underground plant stem producing roots and shoots — zero him (anag)
• With zero help, initially, I'm moving part of plant
• Horizontal underground stem
• Capital inwardly greeting Zambia's rootstock
• Rootstock draws attention to bottom of Shiraz in European capital
• Roots and shoots grow from this underground plant stem
• One puts down roots, beginning to read one last letter in residence
• Republican base harbouring single unknown source of shooting?
• Type of rootstock