Insert the seeds of transplants through an X cut in the plastic. In Oregon's relatively cool summers, this condition doesn't always occur. Black plastic smothers the weeds, conserves moisture, and warms the soil. Irrigation water that goes through the plant openings and around the edges usually is adequate, and no special provision is needed to get moisture into the soil for narrow mulches. Or, if puddles form on the plastic, make a small hole in the plastic at the lowest portion of the pool to allow drainage into the soil.
Less water is needed with plastic mulch, since evaporation loss is less.
A large sheet of black plastic may be used to cover the garden during the winter if a portion is to be worked and planted very early. It will keep down the winter weeds, and the soil will remain dry. Weights or a bark mulch may be needed to keep the plastic in place. These covers increase heat units accumulated by two to three times. Row covers make possible the production of high-quality melons in western Oregon and enhance earliness for many crops by improving vine growth and flowering.