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Soil fertility should be maintained by the addition of fertilizers when necessary. Fertilizer formulations containing lime should be avoided to keep from raising the soil pH. Application of ferilizer may continue into the summer if necessary, but should be discontinued after the end of July to allow the plant growth to harden off before winter. Fertilizer should not be placed near the trunk itself. Plant roots are concentrated away from the trunk, at a distance roughly equal to the "drip line" or edge of the branch canopy - it is there that fertilizer should be applied.
Some attention has been given to foliar application of fertilizer in magnolias. Smithers (1977) and Adams (1984) reported excellent results with a weekly or biweekly foliar application of macro- and micronutrients throughout the summer. Foliar sprays reportedly decrease heat stress of plants as well as provide nutrients in readily available form. Continuous vigorous growth was reported throughout the summer and was most noticeable onplants that had also received foliar feeding the previous year. Better root growth was noticed in treated plants after just one season. Foliar spraying is best done in the evenings to avoid leaf burn, and should be discontinued in the fall to allow time for the plants to harden off. Adams (1984) provides information on price and availability of foliar fertilizers as well as practical information on their use.
Pruning is usually not necessary in magnolias, but may be performed as with most woody plants. Certainly misshapen plants can be pruned to create a better form. Suckers from the understock of a grafted plant need to be removed as soon as they are noticed, regardless of season. Also remove unwanted leaders, keeping only those that are appropriate to shape and height requirements. Any weak, dead, or diseased branches can also be pruned out. Precocious species may be pruned in the summer after blooming has ceased. Summer-flowering species are best pruned in late winter.
Root pruning is sometimes advocated as a means of restricting the growth of a large specimen. This may be done during the dormant season by using a shovel to sever the roots about a yard (1 m) from the trunk of the plant. If restricting a plant's growth is necessary, this is a reasonable way to do it; however, it is preferable to avoid the need to do so by carefully siting all plantings. Some gardeners report using this procedure as a method to hasten flowering time. I do not recommend this. The earlier flowering is the plant's reaction to induced stress (the reduced root system) and is not beneficial in the long run.
Photo above: Magnolia 'Orchid' - Photo by Dorothy J. Callaway.