The magnolia family of trees are not heavy feeders, but can benefit from annual applications of fertilizer to improve slacking growth and bloom. When grown nearby to regularly fertilize expanses of lawn, grass magnolias will not need feeding, as the run-off from the lawn will provide more than adequate feeding to the magnolia roots and surrounding soil.
Conversely, when magnolias are grown near hardscape or in constricted areas such as medians, the roots may not have a full run of ample soil and fertilization is required to help support the tree with basic nutrition. Magnolia trees should not be fed until they reach three years of age, and then twice per year thereafter in the spring and fall.
Organic Fertilizers & Soil Amendments
Use natural plant food and soil amendments to feed your magnolia tree. An ideal organic fertilizer is Espoma's Holly Tone, with a 4-3-4 formulation. Amend the planting soil around magnolias with several pounds of peat moss, compost and well-aged manure to boost the nutrient value. Topdress established magnolia trees each year with the same amendments scratched into the soil surface and watered in well.
Acid Rich Fertilizers
Magnolias are acid-loving plants, and when they are grown in neutral or alkaline soil, they will benefit from an acid-rich fertilizer formulation. Look for a slow-release complete fertilizer product designed for acid-loving plants like Miracid, or any magnolia, gardenia, camellia or rhododendron food with a guaranteed analysis of approximately 30-10-10. Apply according to product label directions and err on the side of underfeeding if ever in doubt. Refrain from using acid-rich fertilizers in soil that is already acidic, as this will not benefit the magnolia.
General Purpose Synthetic Fertilizers
Slow-release balanced and complete formula granular fertilizers are preferred for magnolias over fast-release formulations. Choose a product with a guaranteed analysis of 13-13-13 or 10-10-10, and apply according to product label dosing directions in the spring and again in the fall each year.