I know this might be a ridiculous idea, certainly would not look attractive and I have never tried it so it has not been tried and tested and therefore is not a recommendation.
Those very large cardboard boxes which all the big clothes stores in town throw out to be recycled might come in useful here. Fold in the top and bottom flaps to give the box more rigidity and stand them around the plants while you are away or even just for part of the day when the sun is at its strongest. Some light will get in from the top and the scorching rays will be kept off the leaves and soil around the roots. I
f you use the boxes for only part of the day they can be folded flat when not in use. In the autumn they could go to their original destination, the recycling bin. They might look a little less unsightly if you slit them down one side, turn them inside out so that the plain brown corrugated card is visible and then stick them up again. If you get strong breezes you could put canes inside the box pushed ???into the soil to stake them in place so that they don't get blown onto the plants and break stems etc,
Just an idea ...