Magnolia tree, fertilization. Can I use 12-12-12
The tree was recently trimmed by so called experts. Next spring tree looked bad and lost leaves early
The poor appearance and leaf loss may or may not be due to the pruning. Excessive crown reduction and/or thinning, removal of more than 25% of the foliage, can be stressful and it takes time to recover.
You can use a 12-12-12 chemical fertilizer, but for the best for your tree, I would prefer if it were a high quality product like this, with organic materials and controlled release nutrients and a full range of major and minor nutrients.
Another organic all purpose fertilizer that is widely available: https://www.domyown.com/dr-earth-organic-all-purpose-fertilizer-p-9485.html