I'm not sure how much is too much for garden plants, but in our pool we aim for 5ppm to shock and wipe out any algae. We then maintain at 1-2 ppm for a week or two before shocking again. Not sure how this might apply to garden plants in soil. In the pool sunlight and heat break chlorine down quickly. Extra dirty swimmers use it up, too.

Can you let your recycled water set in heat or/and sun for a few days? Could you throw in some "dirt" to help use up the chlorine? Can you aerate it. Any of these would speed up chlorine removal and help make high chlorine water into low/no chlorine water that is safe for your plants.