Plants placed on the fabric will gain access to soil water through capillary action. For more efficiency you can add edging boards to enclose the nursery bed. This will keep the plants neatly and will reduce the effect of drying winds, making watering more effective. Make sure you sterilize the fabric regularly to maintain a clean growing environment.
You can build you nursery bed of any size you need but it essential to create it on free-draining soil. If the soil of your garden is a heavy clay then you should raise the nursery bed from the soil level. Lay down a plastic sheeting then add a layer of 8 cm of coarse, lime-free sand. Enclose the entire sand bed with edging boards to keep it in place. The edging boards and plastic sheet will retain moisture and ensure that watering is effective and the drainage afforded by the sand will prevent a water-logged environment.
For more efficiency you can add a covering layer of water-permeable woven fabric. This will prevent erosion of the sand by the wind and also the disturbance by domestic animals, keeping the sand clean and hygienic.
A sand bed is more advantageous then a basic nursery bed because it reduces the amount of watering necessary and minimizes the risk of potting composts drying out. There can be build even more complex sand-beds by incorporating drainage pipes and automatic watering systems.