Answer: Acanthus mollis prefers a soil with average moisture that is also well drained. A possible symptom of overwatering could be yellowing leaves at the base of the plant. Your goal in watering a new plant should be to keep the soil evenly moist but not sopping wet. If it rains or if your soil is a bit heavy to begin with, or if the weather is cool, you would water proportionately less. It is usually a good idea to dig down into the soil a little bit and check to see if and when you need to water. Be sure to check both the original potting soil and the surrounding native soil, because sometimes one dries out before the other. Also using several inches of organic mulch will help reduce the need for supplemental watering, so you would also take that into account in determining when to water.
Another possible reason for yellowing would be planting too deeply. The plant should be resting at the same level as it grew in the pot, no deeper. Sometimes the surrounding soil will settle after planting and watering it in, resulting in the plant sinking too low. If this has happened, just dig it out, rearrange to add more soil at the base of the hole and then reset the plant.
I hope this helps you troubleshoot.
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