Garden Updates Cont.: Seed Bed

Before vacation, I planted my "heat lovers"--squash, cucumbers, beans. okra. All germinated and are thriving except the summer squash, a variety called lemon. I suspect it is the state of the bed I planted them in:
If it wasn't the shade, then I wonder if Brassica species like this broccoli exude something that prevents germination.
The parsley and cilantro flowers are now propped up and the seed will be harvested. I removed all but one of the broccoli plants (I want to save some seed) and tried again. If it doesn't work out, I'll use this as my "seed bed" for fall crops. The scallions and leeks are doing well.
By the way, did you know how pretty radish flowers are?