Jobe’s Evergreen Fertilizer Spikes 11-3-4 Time Release Fertilizer for Juniper, Spruce, Cypress and All Other Evergreen Trees (9 Spikes)
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If you are interested in the 9-spike Trees and Shrubs, Lowes has it for $4.88 (15-3-3)
These have worked well for me. Stocked up on some more now.
If you are going to use a lot of these I’d recommend attaching something like thi s to your drill, which makes the process much quicker. There are probably cheaper augers out there, but that’s the one I have.