User blog comment:Zombieman1350/New Achievements/@comment-132.3.37.68-20110624182436/@comment-3977620-20110630194356

When my brother was trying to gain the achievement Sunny Days, he did something similar to what you described. It was during a pool level, and the only zombie left was a regular Ducky Tube Zombie. He kept replacing the Tall-nut and had a Tangle Kelp right behind it. He dug up all of his other plants and started planting Sunflowers where he could. After he reached 8000 sun (the requirement for Sunny Days), he let the Tangle Kelp do its job.