Pyromaniac

The explosive plants are:


 * Cherry Bomb
 * Potato Mine
 * Doom-shroom (With Coffee Bean if needed).
 * Jalapeno
 * Cob Cannon (Multi-use explosive).

You can also use sun generating plants but Lawn Mowers, Pool Cleaners, Garden Rakes, and Roof Cleaners can't be used to obtain this achievement.

You can't use other instants (except the Coffee Bean) like Blovers, Hypno-shrooms, Tangle Kelp, Umbrella Leaf, the Squash, Chompers and Ice-shrooms. Generally speaking, anything that shoots the zombies are not allowed, although you could theoretically plant and upgrade or dig one before it shoots. If you attempt to plant a Cob Cannon, it requires two Kernel-pults, so only plant them when there are no Zombies in the same lane, or you won't be able to get this achievement because the Kernel-pults might kill a zombie.

Note: Wall-nuts, Tall-nuts, Pumpkins and Garlic don't count as plants that attack zombies as they defend. And Graves don't count as zombies as they don't move.

Strategy
You can get this achievement in Quick Play.

The easiest and best way to get this achievement is in Level 1-1. Choose Sunflower, Garlic, Jalapeno, Cherry Bomb, Doom-shroom, Potato Mine and whatever else you may want that don't attack zombies.

As the achievement states, you can only use explosive plants to kill zombies. If you have shooting or lobbed-shot plants, you can't achieve this, but it isn't very different from any other level, so it can be beaten easily. Whenever a huge wave of zombies appear, place 2 Garlic on 2 lanes and use a Cherry Bomb to blow up the zombies, but you'll get Explodonator first, instead of Pyromaniac. If you see too many zombies, use a Doom-shroom to blow all up, but when you're in the final wave, divert more zombies and use a Cherry Bomb and get the money bag and you'll achieve this. You may also want to use twin sunflowers if necessary to rack up your total sun.

Trivia

 * This does not appear in the DS version, because the mini-game, BOMB all together!, has a similar concept.