Magnolia trees (Magnolia spp.) bear scented flowers in spring and summer, the result of growing in a moist, fertile soil in full sun to partial shade. Proper site selection aids in a magnolia's success, especially if it's shielded from harsh winds and dry, alkaline or compacted soils. Keep a magnolia healthy, and its chances for disease or insect pest problems greatly diminish.
Maintaining three general characteristics ensures a healthy and happy magnolia: moist soil, well-draining soil and acidic soil. Select a site with fertile sand, loam or loose clay to increase the likelihood the tree will prosper and grow for decades. Moist, acidic soil allow the tree to tolerate a longer daily exposure to direct sunlight. Ornamental magnolias grown in gardens often do not survive in soggy, flooding soils. If the soil pH becomes too high or alkaline (above 7.5), leaf yellowing results since certain nutrients become less available for the roots to absorb.
Apply and maintain a 3- to 4-inch layer of organic mulch over the root zone of a magnolia. Suppression of weeds, retention of soil moisture and moderation of summer soil temperatures help the magnolia grow. The root system of magnolias extends well beyond the spread of its branch canopy, and these roots remain relatively shallow in the soil. A mulch layer becomes even more vital in keeping roots cool and moist, and prevents lawn equipment or heavy foot traffic from compacting the soil around the base. Use acidic mulches or top-dressing like pine bark, pine straw, oak leaves or coffee grounds to maintain an acidic soil and add nutrient-rich humus.
A magnolia tree should receive between 1 and 2 inches of rainfall or irrigation weekly during the growing season. If it's in more direct sunlight, slightly more water may be required to prevent leaf edge browning. During drought, infrequent irrigation amounts around 3 to 4 inches keep the magnolia green while encouraging roots to obtain moisture from deep levels of the soil. Use organic mulch to retain soil moisture around the tree roots. Cooler soil temperature caused by mulch lessens the plant's need for moisture.
Plant a magnolia in fertile soil and maintain organic mulch over the root zone for a healthy plant. Apply a granular, slow-release fertilizer each spring to ensure nutrients release into the soil across the growing season. A balanced 10-10-10 formula suffices unless a soil test reveals a deficiency of a particular nutrient.
Magnolias attain a natural, tidy and attractive shape without the need for annual pruning. Although dead or diseased branches require immediate removal, branch tips may need length reduction if they become leggy or awkwardly long in the canopy. Reduce the bleeding of sap on pruning cuts by pruning in midsummer or in mid-autumn when growth stops. Tip pruning results in removal of flower buds the following spring.