Courtesy of Paul, H., Victory Garden Vegetables, Cobourg, ON
For me, it’s more the texture of the spinach leaves that change when it bolts, not so much it getting bitter. They’re not as succulent as younger spinach leaves are. It also becomes less lucrative to harvest because the leaves of bolting spinach are smaller as more of the plant’s energy is going into the flower. It’s generally much more cost-effective to harvest from freshly planted beds than a bolting spinach bed. Seed is relatively cheap (especially if you don’t buy the hybrid seeds), so if you have the space, better to stagger several spinach plantings rather than struggle to reap the maximum you can from one bed that is flowering.
It’s tough getting your planting schedule right when you’re starting out. We seem to struggle almost as much now trying to get it right as we did 4 years ago when we started! But you’ll run into that situation over and over again, and you just have to figure out creative ways of dealing with the surplus when it happens. See this suggestion from Abby.