Nitrogen is the principal nutritive element responsible for spurring foliage growth in plants, and this is also true for magnolia trees. If the leafy canopy of your magnolia has become sparse over time, is recovering from damage or simply a period of neglect, a fertilization regimen with ample nitrogen can encourage new foliage development. Magnolia trees are broad-leaf evergreens that require acidic soil and fertilizers designed for acid-loving plants are ideal.
Fertilize your magnolia in the early spring before new growth appears or in the summer or early fall to prevent tender growth in late fall that may not have time to harden off before being damaged by cold temperatures. In warm and frost-free climates, this timing is less of a concern.
Choose a fertilizer product designed for acid-loving plants that is either organic with an analysis of 4-6-4 or a synthetic with a guaranteed analysis of 30-10-10. Apply in an amount recommended on the label of the product in keeping with the size and/or age of your tree.
Cast the fertilizer granules evenly over the soil, starting 6 inches out from the trunk and extending a foot or more beyond the drip line of the tree.
Rake the granules into the top inch or two of soil to nestle the fertilizer in.
Water the soil well until drenched but there is no standing water. Use a gentle rain spray setting on your hose to prevent washing the fertilizer away or creating bunched-up piles of fertilizer granules.