Curcumas can be planted as either dormant rhizomes or as blooming plants.
If you start with a dormant rhizome, plant it during the winter or early spring. If you start with an actively growing plant, wait until April or May.
Curcumas should be grown in well-drained, organic soil in areas with partial sun. Peat, rice husk or coarse sand may be mixed with the soil to improve its drainage abilities. Space the plants about a foot apart; dwarf varieties may be planted a closer. Give the plant and its rhizome plenty of breathing room; dig a hole twice its size, place the plant or rhizome in the hole and fill with soil. Don't plant the rhizomes too deep -- an inch below the surface is fine.
After planting, water thoroughly and let the soil dry. Water daily, but only until the soil is moist, not soaking wet. Already growing plants may be fertilized monthly, giving each plant about one flat teaspoon of 15:15:15 or 16:16:16. Using a fertilizer with too much nitrogen (the first number in the three-number sequence) can lead to weak stems and low flower production.
Keep the soil evenly moist, but do not over water as this can damage the rhizome. During hot weather, you might need to water daily. Using mulch is highly recommended.
Do not water at all during the plant's dormant period. This can lead to root rot and kill the plant.
Once they reach maturity, curcumas are easy to propagate by dividing the rhizome. Dig up a clump of curcumas; rinse the rhizomes and soak in water overnight. As you wash off the soil, rhizomes sometimes separate naturally. If not, break the rhizome between stalks by bending it with the stalks facing outward. Then cut off the stalk, leaving no more than one or two lower leaves.
Dig holes big enough to accommodate each newly separated stalk stump and rhizome section. The little tubers and roots that extend from the rhizome should not be bent or folded to fit in the hole. Plant the rhizomes in the hole and cover with rich soil, just deep enough so the green section of the stalk is above the ground and the white section is below.
Generally, it's a good idea to propagate plants whenever they start clumping or grow too dense. In Thailand, where many curcumas are found, plants are typically dug up, divided and replanted every two years.