[Baz]

I wouldn't use spikes.

Find a balanced ratio granular with a decent micro package and slow release technology and lightly broad cast that under the canopy footprint.

Then watch what happens - in other words, observe - what impact your feeding has on your tree.

If it results in new growth then you know you're on the right track with your feeding method.

How often to feed any living plant depends on different factors but I would say twice a year would be a good starting point in your case. Everything is up for adjustments depending on different factors though, like I said.

This is just my opinion.

You could always contact your extension office for their input, as well.

Nice looking tree. Thanks for your care of it. Best wishes going forward....