Jobe's® 15 Pack 13-3-4 Fertilizer Tree Spikes. These value pack spikes are ready-to-use and provide continuous release feeding for up to 2 months. Specially formulated for acid-loving Evergreen trees and shrubs, they ensure a continuous supply of nutrients below the surface, where the tree's active roots are growing. Easy to insert around the tree's dripline, the slow-release formula lasts all season without wasteful runoff, mess, hazards, or smells. For best results, use Jobe's Fertilizer Spikes for Trees & Shrubs in early spring and late fall.