Raised beds issues with heat

Went out to check on the raised beds today and found that the last two days of hot weather have heated the soil in them to the point of  being worrisome about cooking the roots. I doused the soil with tepid water and hoped for the best, but that's not an everyday solution or I will drown my plants.

These boxes  are about 18 inches high and raised off the ground - boxes were recycled and I like them because I can sit on the edge and get UP again without a problem. I had thought that since they have an air space below that the air would moderate the temperature but that doesn't seem to be happening. So.. how to cool off the soil in them? I would have loved to have built up a rock garden on the sunny side but I don't have any rock nor access to any, nor do I have soil to heap up against the box sides. (I am creating soil in the boxes as it is.) I have got a fairly heavy mulch on them so as to mitigate water loss.

Any ideas or tactics  that someone has tried or think might work?

Straw mulch (2-3") will keep the sun from baking the soil.  Cardboard leaned up against the E, W, and South sides of the raised bed will keep the sun from directly heating the frame works (leave several inches of air space at the bottom).

Ahh   thank you .  The ground itself is not at issue since the boxes are a couple of inches  or so off the ground to start out with. There is a mulch IN  the boxes..but the soil within the boxes still gets alarmingly hot. Most plants seem to like cool roots I understand.  Maybe I will put layers of cardboard faced with scrap wood on the sunny sides, so the cardboard doesn't fly away or melt/sag in the rain. That way I could also leave a 1/2 inch or so of air space on the sides...

I had thought of straw bales stacked along the sides but that would make the thing too wide to reach the middle of the beds.

That might help a bit with evaporation as well. The plants go through a LOT of water in these things as the bottom has open seams. Seems like this is a different sort of gardening sometimes  Thanks for your suggestion.

i used raised beds for a first time this yr.  most my plants were surrounded with a layer of newspaper and then covered with a roughly ground up wood chips.  the free stuff from the transfer station.      all this helps keep the soil nice and moist.  i water very very little this yr.  most any watering was done on my blueberry plants.  everything else has done surprisingly well.

I think it would help immensely if the bottoms were not   above the ground an inch or two.  I should have taken the bottoms out but wasn't sure about whether I might want to move them. (Also, the height now is just perfect for being able to sit on the edges and get up again without difficulty, the lower it is the more of a problem caring for things will be.) If the roots could reach the ground it would make a world of difference in a lot of ways. We don't normally get 95 degree weather so it wasn't so clear before what a problem this could be.

These are sort of big window boxes sitting on the ground so the heat penetrates right into and through ..the ones I planted too thickly don't have problems with evaporation but the size of the plants..I have some tomato plants which would apparently be happy with about a gallon of water a day each  sigh. they all have masses of fruit forming though so need the fluid. One box with fewer plants,  lollarossa lettuce and a couple of tomatoes, is doing fine and looking quite spectacular. But those needed water to stop the heat from cooking the roots when it was so hot.

The cardboard against the sides seemed to help with keeping the soil a little cooler but the heat did a number on most of my peas before the cardboard was put on, even with a mulch already in place.

I think that after the season is over I need to empty the boxes and knock out the bottoms and that will solve a host of problems. Maybe will simply extend the sides so the height doesn't change, though not exactly sure how stable that would be for sitting on. Also considering making  sides out of the styrofoam that grapes often get shipped in and which just gets tossed, if they are covered with a scrap wood wall then that should save the styro from degrading in the sun and will prevent the soil from getting SO hot.  Anyone know how to cut styrofoam so it doesn't shatter bits of itself everywhere?

use different type of styrofoam.  go thicker, which is costly but has a better R value. or use the thinner "fan fold" type.  both are easy to cut.  no shattering.

heated wire will melt a straight line right through it too. 

but this styrofoam is free and headed for landfill otherwise so double value    Unfortunately it seems that nobody recycles stryofoam at all and  most of it apparently lasts forever in landfill so anything that keeps it OUT of them in a useful way seems helpful..

Heated wire? Thanks for the tip!  hmm sounds like something to be done outside though as most heated stryo gives off  unhealthy  gasses. Is there some sort of electrical tool that has a heated wire?  I have quite a lot of this stuff to cut

Don't forget to cut back on watering your tomatoes once they reach full size.  Too much watering at this point causes them to soak up too much water, which means they will get watery and lose flavor, and they may also start splitting...at this point, the skin can only stretch so much before it bursts.