To master PvZ Adventures, you need proper strategy for each level or stage in one Map. The most significant thing that requires planning is the Plants that you are going to use. Do research on the level 6-18 first to figure out the best options.
To pass level 6-18, choose only one kind of Sun producing Plant that you prefer: Sunflower, Twin Sunflower or Power Flower, to save Tray Slot. Put them early in battle field with the lowest possible amount of offensive and defensive Plants, to reap the benefit of gaining most Sun in a match. Place short range shooting Plant first and longer range Plant further back. Remember to put defensive Plants like Wall-nut or Hard-nut at first line of defense to protect your Plants on level 6-18.
Choose your Plant according to current level to deal with Zombie weakness. Find out what Zombie type you are going to encounter and use their weak spot against them. Snow Pea and Ice Queen Pea are common Plants to use against all Zombies especially fast moving Zombies due to its slow effect. It is also very effective in removing special ability of Rocket Zombie and Gas Can Zombie with just one hit but it is rendered useless by Ice Block Zombie. Hence, if there are Ice Block Zombie for a level or stage, use Flaming Pea to break it with one hit. It is also effective against Barrel Zombie by breaking the Barrel instantly with one hit. Magnet Plant is needed only occasionally when Zombies like Buckethead Zombie, DJ Zom-B, Football Zombie and Mall Cop Zombie appear, but not necessary. Instant kill explosives are meant for very tough Zombies like Gargantuar and massive Zombies like Conda Leader and Conga Dancers. Zombie Freeze and Zombie Zapper Boost are used against fast moving Zombies like Barrel Zombie, Football Zombie and Rocket Zombie. For difficult rounds, use more expensive and powerful Plants like Shamrock and Bamboo Shoot.
Apart from this, you also have to choose your Plant wisely according to the Path on level 6-18. Use the Plants which best cover a certain Path pattern. If the Paths are joined that no Plants can fit in between, pick powerful Plants with special effects using your Tray Slot wisely. One-instance Plants are great choice too.
Plants vs Zombies Adventures walkthrough guide level 6-18 help – Youtube video
See the video shown below for Plants vs Zombies Adventures walkthrough guide level 6-18 help: