Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
Due to dry weather, a significant amount of plastic mulch has been laid this year in dry soils and in soils with more clods than normal. This can be problematic for a number of reasons. The first is related to bed heating. For effective heat transfer, plastic mulch should be laid tight on a firm bed and the soil should be moist. It is hard to fully wet beds with the drip system once they have been laid, especially in sandier soils. Moisture is also critical for heat accumulation, because water absorbs more heat than soil minerals. In dry and cloddy soils much of the heating benefit of the mulch is lost. Root growth will be slowed and crops will be delayed. Another issue is water movement in the bed. Clods create large air spaces that limit capillary water movement thus reducing how much of the bed that can be wetted during an irrigation event as drip irrigation is started. Where overhead irrigation is available, irrigating soils prior to working ground and laying plastic is an option in dry conditions.