Cucumbers (Cucumis sativus L. 'Loeica') were grown in a specifically designed urethane based recyclable plant growth substrate (UBS) and rockwool (RW) under a recirculating hydroponic production system to: 1) evaluate the performance of UBS in a greenhouse hydroponic production system, and 2) compare the effectiveness of two irrigation schedules on cucumber production using UBS. Plants were fertigated either by schedules 1 or 2. For irrigation schedule 1, plants were fertigated to an extent that 25% leachate was expelled from the RW slabs per day; and for irrigation schedule 2, plants were fertigated at a higher frequency throughout the day at a rate of 1.6 times the volume of schedule 1. Results showed that the UBS seedlings were significantly shorter and one leaf stage behind the RW seedlings during early stages of plant development. This setback in plant growth resulted in delayed flowering and ultimately affected cucumber production. The first USB cucumber fruit harvested was delayed by three days when compared to RW plants. Several weeks after transplanting, plants on UBS did catch up to plants on RW in terms of leaf number and plant height. Eventually, over a 27 day harvest period there was no significant difference in cucumber production or quality between plants on these two growth substrates in terms of fruit length, circumference and total fresh weight. However, irrigation schedule 2 produced significantly more fruits than schedule 1. There was no significant difference in fruit weight per plant between the two substrates under watering schedule 2. The results of this study confirmed that irrigation is extremely important for crop production and that with some design modifications there is potential for the UBS to evolve into a competitive plant growth substrate for greenhouse soilless crop production.

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