A multi-ion sensing device, based on ISFETs, is described for horticultural applications. The advantages of a new packaging technique based on back-side contacted ISFETs are outlined. The basic pH-sensitive ISFETs can be modified to, e.g., potassium-sensitive devices by using neutral carrier-based membranes and an intermediate hydrogel. Both membrane and hydrogel are chemically anchored to the ISFET surface and the ionophore is chemically bonded to the membrane. It is shown that these chemical modifications of the membrane system lead to an increased lifetime for the sensor.