Granted it's a very hot spot - afternoon sun and the hot house brick reflecting the heat. But mostly I blame the rubbish soil. It's practically dust, that lifeless fill dirt they put around foundations. It dries out incredibly easily and once dry, water just pools on top leaving huge pockets of dust below. I added some compost last summer but you wouldn't know it. What I should have been doing was adding more and more all winter long and letting the worms and bugs slowly turn it into decent soil.
So now I'm trying to make up for lost time. You can see in this photo how shriveled the leaves are from the heat. I started by brushing back the mulch and scattering some "Saturaid" (some kind of commercial soil additive that's meant to retain moisture; just looks like coir powder to me). On top of that went a few handfuls of clay kitty litter, that white stuff. From what I understand it's one of the quickest ways to get more clay into your soil to retain moisture. You just have to be careful not to let it cake up into a glob when it first gets wet.
So the moisture-retaining agents were important, but more important is to get some more organic matter into the soil. For this I went to the compost heap. My heap has four sides but the back is pretty close to the fence so this was the first time I'd tried to squeeze my hands back there to shovel some compost from the back. And what compost! Because it'd been sitting there for almost a full year, it was black, crumbly, and full of goodness. Just look at all those worms! Unfortunately it was also full of earwigs who like to nibble young growth, so there was much squashing.
After that each plant got a good dose of water with some seaweed solution to help them get over the heat shock. No fertilizer though, the last thing they need right now is to put out more tender new growth to get burned in the sun. Hopefully the compost will help the soil hold more moisture, and I'll be sure to keep topping it up every month or so until I'm happy with the soil in that bed.