Are you talking about a outside fish pond? What kind of plant is it? If everything is healthy in there I think you could. I would recommend rinsing it in clean water and maybe keeping it a bucket with clean water for a about 1 day to make sure theres nothing on it and rinsing it again before you put it in your tank. I've used rocks from my pond in my tank to help cycle it and it was fine. Also you can get light made especially for planted tanks since that new plant would be used to sunlight so it would need good light to keep growing healthy indoors. I hope this helps you!!!
