Answer: Plastic edging does tend to warp in the heat. Sometimes you can pound a few stakes in the ground to redirect it, but sometimes you can't. Replacing should be easy, though, because the trench is already there and once you pull up the plastic edging you can place the new edging material in the same trench.
Bender board comes in long rolls and conforms to even the tightest curves and turns. It doesn't warp and it lasts for at least 5 years.
Metal edging is preferred by professional landscapers. It's pliable, may be painted and lasts forever, but it's expensive. If the soil is soft, you can install metal edging by laying it along the border of your garden bed and tapping it in place with a hammer, using a piece of board to cushion the blow. If the soil is hard, dig a shallow trench first, then lay the edging in the trench and fill with soil.
Borders of stone, concrete or brick are the most expensive but also the longest-lasting choice. Unless the stones are fitted together with mortar, however, weeds and turf grasses will quickly grow between the cracks.
Cement or brick pavers are reasonably inexpensive. Bricks tend to be more attractive and versatile since you can use them on their side, set them end to end or lay them on a diagonal pattern.
Many types of precast border stones are also available at garden-supply stores. Interlocking pavers are perfect for do-it-yourselfers. They're expensive but may be used in a variety of ways, including side by side to create borders or stacked to build raised beds.
Best wishes with your landscape!
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