Killing a termite colony in the ground requires targeted treatment. One effective method is using termite bait stations, which are placed in the ground around the property. Termites are attracted to the bait, consume it, and share it with their colony, eventually leading to the colony's decline. Another approach is using liquid termiticides to create a barrier around your property, which affects the termites if they attempt to cross it. Professional assistance is highly recommended for both methods.