Those plastic hose repair fittings will last a long time as long as they are sized right (should be a snug fit). I still prefer brass for the male hose ends and various adapters though as I've damaged too many plastic ones. Look in the Grainger catalog. They aren't cheap but they never wear out either. Like Anna's shovel, you get what you pay for.

In an outside environment thermoplastics (like the hose and probably the clamp) will deteriorate significantly in a couple of years due to UV radiation which breaks the chemical bonds in the material. Most so-called "soft" plastics are usually made soft by mixing in plasticizers. These plasticizers invariably leak out into the environment. Some of them (phtalates e.g. in PVC) are known endocrine disruptors and are best avoided.

Having said that, thermosetting materials will last much longer than thermoplastics but are more expensive to make and cannot be melted once formed. The so-called GRP (glass-reinforced plastic) uses a thermosetting material, usually polyester, in combination with glass fibers.

Most common small plastic parts that you'll see are thermoplastics, except for melamine dinnerware and cladding for chipboard furniture and "formica" panels. Car tires are usually made with thermosetting rubber.

Sounds like the hose repair pieces will probably last as long as the hoses since we got the cheapest ones. (We were dirt poor when we started our irrigation system.)

If you want to make the hoses last longer, either put them away out of direct sunlight when not in use, or bury them under the ground. Both options should prevent UV from damaging the materials. It would also prevent damage from the mower.

You can think of thermoplastics essentially as cold cooked spaghetti. The jumbled long strands stick together. But heat it up, and the mass becomes malleable. And if you start cutting the strands one by one (like UV does to the molecular chains of plastics), sooner or later the mass will fall apart.

Mark suggested burying them too, but that's a big task! We're currently in "no nonessential tasks" mode for the rest of the summer.