Most seedlings need minimum safety in U.S. Department of Agriculture hardiness zones 9 and 10. Tomatoes, peppers and warmth-loving crops might need some safety because great but above freezing temperatures can stunt seedling development or cause blossom fall in plants when spring temperatures fall below 45 degrees Fahrenheit. Milk jugs offer a short term answer it is possible to recycle or pack a way, unlike other construction or a cumbersome greenhouse.
Measure 4″ up in the underside of a milk jug. Mark a line as of this measurement using a marker.
Cut off the bottom part of the jug over the line that is marked, using a utility knife.
Remove the cap in the jug to supply an air-vent. The cap is required in locations that experience freezing temperatures.
Set the milk jug on the seedling in the backyard. Before the seedlings grow tall enough to contact the sides of the jug remove it.