Mexican heather (Cuphea hyssopifolia), also known as false heather, is a member of the family Lythraceae. Native to Mexico and Guatemala, Mexican heather is a perennial evergreen that prefers warm, tropical climates such as those in USDA planting zones 9 and 10. It will live in zone 8, but might die to the ground in winter and return in spring. It will grow best planted outdoors in these planting zones. In all other zones, Mexican heather should be planted in containers where the climate can be controlled.
Bring container-grown Mexican heather indoors, in the event of a freeze or frost, as it is very cold-sensitive. Place the container in a sunny, warm area and do not place outdoors until the weather has warmed.
Water the soil around the Mexican heather well, being sure it reaches down to the plant's root system, at least 24 hours before a frost or freeze. This will give the plant's root system extra protection during the cold weather and keep it warm.
Mulch around the plant with cypress mulch, pine bark, leaves or pine needles to help the soil retain warmth. This will also allow the soil and root system to retain moisture.
Cover the Mexican heather with a sheet, blanket or some other type of covering made out of cloth. Plastic will burn the plants once the sun rises. Place bricks, dirt, wood or some other type of material on top of the cloth to keep it in place if the weather is windy as well as cold.
Place a 60-watt outdoor light under the blankets covering the Mexican heather, to help produce more heat. String a strand of Christmas lights around the plant's foliage, if a hard freeze is not expected. This will give the plant a constant supply of heat, as well as a festive look.