Marigold

The Marigold is the only money producing plant. It is also the first plant the player receives for their Zen Garden.

Suburban Almanac Entry
Marigold

Marigolds give you silver and gold coins.

Special: gives coins

Marigold spends a lot of time deciding whether to spit out a silver coin or a gold one. She thinks about it, weighs the angles. She does solid research and keeps up with current publications. That's how winners stay ahead.

Cost: 50

Recharge: slow

Usage
Planting the Marigold costs 50 Sun. Every 24 seconds or so it produces either a silver ($10) or a gold ($50) coin. Gold coins are rarer than silver ones.
 * Note: These are best used in conjunction with Gold Magnets, as you'll probably be too busy tending to your other plants to collect the money yourself.

Strategy
Marigolds are great space fillers in early levels (when playing Adventure Mode again) due to the lack of stronger zombies and potential for hoarding excess Sun. In later levels Marigolds take up too many valuable slots to be worthwhile (especially on the Roof).

Another strategy is to plant an entire row of Marigolds with a Gold Magnet and one or two Garlic/Imitater Garlic plants in the front to divert the zombies away, although Gargantuars, Catapult Zombies and Zombonis can get annoying sometimes.

Marigolds are commonly used in the Mini-game Last Stand for Gold Farming.

Trivia

 * Marigolds are the only plants that can be bought for the Zen Garden, with the exception being the plants that you can buy from Crazy Dave in the iPod/iPhone version for $7500 each.
 * Though Marigolds planted in the game modes all have white petals, Zen Garden Marigolds come with many different petal colors (Grey, Red, Pink, Orange, Yellow, Green, Blue, Cyan, Purple and Magenta).
 * When a Zen Garden Marigold is highlighted by the Watering Can on the DS, it may change color instead of lighting up.
 * The color it changes to depends on the color of the Marigold, and the petals may not change entirely, leaving small patches of the original color.
 * Rather than starting as a sprout, Marigolds in the Zen Garden start as little flowers with three petals.
 * Marigold and Cactus are the only two plants referred as female.
 * You will get a Marigold in your Zen Garden before you get it in Adventure Mode.
 * In Versus Mode, the use of Marigolds is prohibited to prevent Versus Mode from being used as a tool for Gold Farming.
 * During a level's final wave, both Marigolds and killed zombies stop producing coins. Even newly-planted Marigolds will only produce three coins or so before stopping.
 * This glitch does not appear in the Android version.
 * Marigold sprouts can be seen growing in the loading bar on the title page before a Zombie head shoots out of the lawn.
 * The fact that it produces coins is a pun on its name which has the word gold in it (Marigold).
 * The Marigold actually resembles a common daisy more than a marigold.
 * This is one of the few plants that don't have any offensive or defensive abilities.
 * The Marigold is one of the plants that glow. The others are Sun-shroom, the Magnet-shroom, the Gold Magnet, the Sunflower and the Twin Sunflower.
 * If you look closely, you will see a single tooth on the Marigold's mouth. She shares this trait with the Cattail and the Starfruit.
 * The Marigold is one of the three flowers in the game (the others being Sunflower and Twin Sunflower).
 * Since Marigolds are more commonly used in Last Stand for Gold Farming, it is often forgotten that they have a slow recharge rate. This may be due to the fact that you do not need to wait for it to recharge between waves.
 * You can tell the direction a Marigold flower is going to face, during the first stage which is right after purchasing it, the sprout will face either left or right, if it faces right, the Marigold will face left when it becomes a flower and vice versa.
 * The Marigold is one of the plants that's not available in Versus Mode. The others are Lily Pad, Tangle Kelp, Sea-shroom, Blover, Flower Pot and Plantern.