Freeze and Thaw in the Spring can cause water to melt and pool around plastic Irrigation Parts. Then when the water freezes again, because the temperatures drop, standing water can turn to ice causing the plastic to harden and crack. This is most likely to happen at the elbow joints of the irrigation system; bottom of the sprinkler attachments, seldom the valves, and low points of the mainline. Another issue to keep in mind, when a small drip is being released from the main shut off, that can fill the line slowly throughout winter which then can freeze and crack the mainline parts.