This accidentally turned into a nice demonstration because the various leafy greens germinated in their soil blocks at different times and were planted out at intervals of a few days.
My compost method is known as "slow" or "cold" composting. This pile it and forget it method doesn't produce enough heat to reliably kill weed seeds. Some will die of old age before the compost is used, but others will survive.
That means my just-filled raised beds were filled with unsprouted weed seeds. They sprouted as soon as they got light and moisture, leaving me with a weedy mess of a vegetable bed like this.
|Weedy mess and transplanted chard seedlings|