Alyssum

Alyssum makes a fantastic mulch between vegetables rows because it grows so quickly it will keep weeds from taking hold. It has very short, unintrusive roots, and is easy to pull out when you no longer require its services. Meanwhile, the tiny white flowers will attract beneficial insects and pollinators, and increase the chances of good fruit set for fussy vegetables like squash. Alyssum is one of the longest blooming garden flowers, as well - it only gets killed off  by hard frosts in the fall.
It is incredibly easy to start Alyssum from seeds. The tiny seeds can be scattered on the surface of some potting mix indoors any time between early March and June. Just lightly press the seeds into the surface of the soil, and keep the soil moist. Most of the seeds will germinate after only a few days.