You are VERY observant Bobinky!!
I have used cardboard to cover the space in between plants in the raised beds, you can only see it in one of them. This is because we have Devil Grass or Quack grass and I have pulled and Pulled and PULLED it out>>>>>but there is always MORE!! The cardboard is an attempt after pulling as much of the stuff as possible, to keep it from growing back. This is an experiment and I am going to see how it works. Thus far it is working well.
The white stuff you see covering the edges of the raised beds are the ends to the Barge Covers that the raised beds are piled into. Once again, the grass is horrible>>>it grows through almost anything>>>cardboard, plastic, newspaper, you name it, with in just a month of two the stuff is growing all through the beds.
The rizomes on the nasty DEVIL WEED is POINTED and actually CUTS through anything that it is possible to tear, cut or pierce.
One year, I tried putting all my composted manure and soil on top of an old canopy. I raised the sides up over the tops of the concrete blocks and WALA!! Had almost no grass growing in the beds!
Sooo>>>> I found someone selling barge covers at our local Sale Barn. These are used on the river barges on the Mississippi, which is not that far from us. Bought about 5 of them and planted 3 so far. They are about 15 - 20 feet wide and about 50 feet long. I set them on the ground, place all my soil inside the barge cover and then rim the outside with concrete blocks. There is a tremendous amount of barge cover left. About 1/2 of it. I have cut it to "fit" the block form. What is left over is more of the cover and some netting, which I will use to shroud my fruit trees if I can ever get any to grow!! Also, next time I will not place the beds in the center of the OOPS!! I mean barge cover, but off to one side and have more available to use for more beds......