well, in green house monitoring, we used to monitor the moisture level of soil, humidity, temperature level. so if we set up a WSN for huge area of green house it requires more number of senor node and may multi nodes sense the same parameter. in such case data aggregation can be performed to eliminate the data redundancies.
From our experience, the main challenge is related with limited dimension of buffer size and in some instances, with limited capacity of the employed micro-controller. Hope it helps! All the best