Is planting the land in the second half of the lunar month a superstitious belief, or does it have scientific significance and is approved by Islam?

It cannot be definitively stated whether planting in the second half of the lunar month is based on a scientific reason or a superstition, because that requires knowledge of the nature of plants. If its benefit is scientifically proven, there is no harm in it, like other worldly matters based on experimentation and experience. However, if it is not proven, then it is a superstitious belief that might lead to polytheism (shirk (definition)), especially if one believes that the moon or planets are what cause plants to grow or rain to fall.