- Create a small berm of soil around the base of a newly planted crape myrtle. This creates a catch basin for irrigation water for the first 12 months. Rainfall is not enough to ensure the crape myrtle's root ball does not dry out. It's vital that both the original root ball and the surrounding soil remains evenly moist to help coax roots to grow outward and establish in the garden. Water the tree once to twice a week for the first 60 days, but irrigate deeply during any unusually dry periods the first year after planting. Place a 3- to 4-inch mulch layer over the soil to help retain soil moisture, especially during the heat of summer.
- Crape myrtle trees grow well in any well-drained soil, from sandy to clay. If the tree is in a low spot or the soil doesn't drain quickly after rains or irrigation, the overly wet soil leads to root rot. As roots die, it often is accompanied by yellowing and dropping of leaves in the canopy. Conversely, sandy soils may need more frequent irrigation as compared to loam or clay garden soils. Sandy soils drain and dry out much more quickly and thoroughly that other soil types.
- While usually not a problem on newly planted crape myrtle trees in the landscape, diseases or pests can stress a plant and cause leaf yellowing. If the crape myrtle is located in too shady of a site, it can lead to an aphid infestation on new growth. The aphids' excrement, called honeydew, leaves a sticky film on leaves, which is then infested by fungus. Sooty mold looks like black dust, and blocks light from reaching the leaves. Overly wet soil couple with too much shade can also cause leaf spot and powdery mildew diseases to occur, causing stress and some leaves to yellow and later drop away.
- Crape myrtles grown in containers at nurseries often have slow-release fertilizer granules already on the root ball at planting time. This sustains the tree for up to six months after planting. Sandy soils often lack nutrients to keep leaves green. A half-dose granular fertilizing about 30 days after planting can diminish any concerns of infertile soil. In the next two years, fertilize the young crape myrtle tree in early spring as leaves unfurl and again two months later at the full rate recommended on the product label.
- Although crape myrtles are grown throughout U.S. Department of Agriculture plant hardiness zones 7 through 10, it's better to plant them in early spring in zones 7 and 8. This means they will endure intense heat during the first six months after transplant. Watering is vital to preventing yellowing leaves and encourage rapid root growth and establishment. Elsewhere, crape myrtles may be planted any time of year, as the roots grow even when the tree is without leaves in the mild, warm winter months.
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