An irrigation pipe coupler can engage an open end of an irrigation pipe with its forward end. The coupler has a nipple and an outer collar. The nipple has an outwardly projecting barb and the collar surrounds the nipple and has an inwardly projecting bulge. The collar is slidably moved along the nipple between forward and rear terminal positions while being kept spaced radially outwardly from the nipple via a peripheral gap that is re-defined for each new position of the collar along the nipple. At each such new position, the gap has a narrow region measured in the radial direction where the collar is closest to the nipple and the narrow region gets smaller at least during at least part of the forward movement of the collar along the nipple. A window formed in the collar allows an operator to see an irrigation hose inserted into the gap.