A: You need to fertilize more aggressively.
Raised gardens need more frequent watering than in-ground, and those waterings rinse away soil fertility. Bulk bed mixes contain a lot of composting woody material, which tends to suck up available nitrogen in order to break down. That’s two reasons your plants need a good feeding!
Apply a cup of your favorite vegetable garden fertilizer per 4′ x 4′ square of the bed, and as many as two cups of fertilizer if you’re using an organic fertilizer. Re-apply every four to six weeks, and you’ll get the results you were looking for.