Crepe myrtle fertilizer is a basic, all purpose mix of nitrogen, phosphorus, and potassium. Select an 8-8-8, 10-10-10, 12-4-8, or 16-4-8 blend of general, liquid, or granular fertilizer. These blends provide the basic levels of nutrients needed to keep the crepe myrtle healthy. The key to using crepe myrtle fertilizer is to apply it properly.
With a young crepe myrtle plant, fertilize frequently to help it develop a strong, healthy root system. Use one teaspoon (1/6 fluid ounce) of fertilizer around the base of the plant monthly. Start when you plant the crepe myrtle or, if it is an existing plant, in March, and continue through August.
Once established, apply crepe myrtle fertilizer by broadcast application in the spring, using one half to one pound (.23 to .45 kg) of fertilizer for every 100 square feet (9 square meters) of ground. For best results, apply the fertilizer before a rain. If that is not possible, water the area where the crepe myrtle fertilizer was applied. This helps the fertilizer sink into the soil, making it more available to the plant.
It may seem that if some fertilizer is good, that more is better, but that is not the case. Applying too much fertilizer, or applying fertilizer too often will stimulate leafy growth in the plant. When this happens, the crepe myrtle will have an abundance of leaves but few blooms. Not only is this less attractive, but it is not good for the tree either.
Crepe myrtles are known for low maintenance requirements that repay the gardener with an abundance of flowers. With minimal care, the crepe myrtle provides years of flowers. The crepe myrtle is drought resistant, and is not typically plagued by pests or disease. One way to improve the hardiness of the plant is to take extra time during the planting and early growth period to ensure the plant gets a strong and healthy start.
Prepare the crepe myrtle for planting by digging a hole that is at least two times the size of the root ball. This gives the roots plenty of room to spread into the surrounding soil. Place the crepe myrtle into the hole, and replace the soil around the shrub, making sure to keep the plant at the same level as it was planted in the pot. Apply crepe myrtle fertilizer at planting. Water after planting, and weekly for the first two months. Mulch around the plant with pine straw or other mulch to insulate the roots from extreme changes in temperature.