Upgrade plants

 are powerful Plants that must be bought from Crazy Dave's Twiddydinkies. To activate an upgrade, it must be planted on its weaker variant. They are expensive in terms of both Sun and Money.

Plants
There are a total of 8 upgrade plants.

Gatling Pea
The Gatling Pea shoots four peas per round of fire.

Twin Sunflower
The Twin Sunflower provides two units of Sun every time it emits yellow rays.

Gloom-shroom
The Gloom-shroom shoots four bursts of Area of Effect fumes into all adjacent spaces per round of fire.

Cattail
The Cattail shoots two Spikes per round of fire that automatically home in on a target and can cover the entire lawn.

Winter Melon
The Winter Melon lobs frozen Melons that deal heavy immediate damage to its intended target, and some damage to nearby zombies, and a slowdown effect to all zombies hit.

Gold Magnet
The Gold Magnet periodically collects Silver Coins, Gold Coins, and Diamonds for the homeowner.

Spikerock
The Spikerock spikes zombies at a rate of two damage per round of fire. It can sustain nine Gargantuar blows or tyre pops. Its spikes are indicators of its remaining health, as it loses one big spike every three Gargantuar blows or tyre pops.

Cob Cannon
The Cob Cannon is a reusable Cherry Bomb with a recharge rate of 36 seconds. Clicking/tapping the Cob Cannon will allow you to select where to fire the Corn Cob.

Trivia

 * Upgrade plants are not available in the online version. Maybe because of the plant restricton.
 * The Imitater cannot imitate an upgrade plant for obvious reasons.
 * The Player may not have the Upgrade Plants at the time of purchase.
 * However, you can upgrade an Imitater, it just won't be black and white.