Though field nurseries have traditionally functioned without irrigation, they sometimes require irrigation to ensure survival and increase growth of more mature plants. For optimum growth and survival during droughts, field growers often maintain drip irrigation systems throughout the production areas. The average water requirement for field grown nursery crops is one inch per week, from either precipitation or irrigation.
Irrigation systems for field-grown nursery crops have the potential to increase plant survival rate and to increase growth. Watering immediately after planting is a necessity for establishment. As plant density increases, it is more efficient to water with a permanent or semi-portable irrigation system. The primary reason for installing an irrigation system is to increase growth throughout each year.
Large-caliper shade trees are increasingly being produced with drip irrigation. Due to the wide spacing used in the production of shade trees, drip irrigation is most appropriate. Drip irrigation is a low volume, low-pressure system. Water application is gradual, and less water is lost to runoff and evapotranspiration. Trees reach a marketable size more quickly and with a more compact root system. Drip irrigation is especially suitable for the clay-rich soils of the Southeastern United States. These soil types encourage lateral as well as downward water movement. Roots proliferate in these moist areas creating a dense root ball. Drip irrigation also helps reduce weed pressure because weed seeds are not germinated by water distributed over large areas.
A disadvantage of drip irrigation is lack of frost protection for flower buds that can be achieved with overhead irrigation. Another disadvantage is the difficulty of watering in preemergence herbicide applications. If drip irrigation is used, preemergence herbicides need to be applied well before expected weed emergence or just before a rain event to achieve adequate control.