Jamieson, Fausset and Brown on 2 Chronicles 31:6-7

6-7. and laid them by heaps--The contributions began to be sent in shortly after the celebration of the passover, which had taken place in the middle of the second month. Some time would elapse before the king's order reached all parts of the kingdom. The wheat harvest occurred in the third month, so that the sheaves of that grain, being presented before any other, formed "the foundation," an under-layer in the corn stores of the temple. The first-fruits of their land produce which were successively sent in all the summer till the close of the fruit and vintage season, that is, the seventh month, continued to raise heap upon heap.