I place my plants in a large saucer or tub containing about an inch of soapy water, then flood the potting soil with a soapy-water solution (a little Dawn dishsoap in water). The soapy water will kill the ants, which can't get away because of the water in the saucer/tub. When the ants climb up the pot or up the plant, I spray the soapy water on them. But don't do this in sunlight because it can burn the plants. After the ants are dead, I spray clean water on the plants to remove the soapy water. I've never had a plant die, and I put all my plants out in early spring, each year. Sometimes, I'll water my plants with soapy water just to make sure they don't contain any ants before bringing them in. It's a cheap solution to an aggrevating problem.
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