Thanks everyone.

Its really easy, follow the dead flower stem down and when it is at the height you want it just cut it with secateurs/ scissors. I usually take mine down to about 12" and then the side shoots often flower later in the year.

Maltese Cross plants are very easy to grow. The like full sun. They will tolerate partial shade. They prefer loose, rich soil that drains well. Maltese Cross plants are drought tolerant, preferring soil on the dry side. It is important to avoid wet soils. Plants will not do well and will likely die in wet soils. Add a general purpose fertilizer when planting them, then once a month after that.

Once your Maltese Cross plants are established, they should grow well with few problems. Keep well weeded. Apply a layer of mulch to keep the weeds down. The "hairy" leaves and stems can catch garden debris. Be careful to keep them clean, while working with the plants.
The plants will flower in the second year. Then, watch the butterflies flying over to the blooms. Deadhead the spent flowers, to promote continuous blooms all summer and into early fall. Remove the flower and entire flower stem.
Maltese Cross plants are heat and drought tolerant. But, water them during the driest periods of summer. They will do well in mid-summer's heat.
Jerusalem Cross can be invasive. Use border edging, as needed. Edging should be four to six inched deep in the soil.