Karpas is found on the Ki'ara in the lower left corner according to most minhagim. Very quickly after Kiddush and U'rchatz we find ourselves ready to eat the karpas. Should we take it from the ki'ara and leave a vacant space where it once resided spoiling the completeness of the ki'ara or should we leave it there and bring in other karpas from the kitchen?
The Piskei Tshuvos brings from the Vayaged Moshe that we eat the karpas from the ki'ara since the whole point of the ki'ara is to provide us with what we need for the seder. Nevertheless he says that we leave a little karpas on the ki'ara so that it can remain complete throughout the hagada.
The Ben Ish Chai says that Al Pi Kabbala the ki'ara should remain intact until after eating the Matza and Maror. Since you must not disgrace the food on the ki'ara it should be eaten during Shulchan Oreich. Others hold that the ki'ara should remain intact during the entire seder and it should be eaten during the meal on the next day.
Important Note: We try to convey the Tshuva to the best of our ability. We admit that our understanding may not be accurate. One should learn the tshuva to verify the accuracy of our interpretation. Please also understand that this Tshuva may not be the final word on this topic. One should consult a Rav before drawing any conclusions.