Spikeweed

The Spikeweed is a passive plant that attacks, dealing normal damage to any zombie that walks on it. They can only be planted on the ground (not even Lily Pads or Flower Pots) and does 5 attacks in the time it takes any normal speed zombie. (Faster zombies only take two hits) to pass over it. It will also pop the tires of the first Zomboni that drives over and a Catapult Zombie. Since the Spikeweed attacks from below, it can bypass shields.

Suburban Almanac Entry
Spikeweed

Spikeweeds pop tires and hurt any zombies that step on them.

Damage: normal

Range: all zombies that walk over it

Special: can't be eaten by zombies

Hockey is Spikeweed's obsession. He's got box seat season tickets. He keeps close track of his favourite players. And he consistently cleans up in the office hockey pool. Just one problem: he's terrified of pucks.

Cost: 100

Recharge: fast

Standard Levels
Plant Spikeweeds in front of Wall-nuts, Tall-nuts or Pumpkins. Most zombies can't harm it, and will be continuously damaged as they try to eat the defensive wall. Spikeweed is especially important for levels with Zombonis, and placing the Spikeweed on the first row will prevent the Zomboni from laying any ice at all (preventing the appearance of the Zombie Bobsled Team). Note that Gargantuars can destroy Spikeweeds in the same way as they can any other plant.

Vasebreaker: Hokey Pokey
Try to lay down either a row of three Spikeweeds or one Spikeweed in front of a Wall-nut to kill the zombies. Timing can be everything, so if you see a Wall-nut, go ahead and break a few vases on the right hand side to see if a Wall-nut will be needed there. If no zombies appear closer than the fourth row from the left, put the Wall-nut on a different row, and lay down Spikeweed instead. Buckethead Zombies are the exception to this, as you can't kill them with just Spikeweed - make sure to have a Wall-nut in place or use a Squash to kill them.

Trivia

 * Jack-in-the-Box Zombies, Zombonis, Catapult Zombies, Gargantuars and Giga-Gargantuars are the only zombies capable of damaging Spikeweeds and Spikerocks. This does not include Bungee Zombies, which can steal them but not hurt them.
 * Even though Spikeweeds can't be planted in Flower Pots during levels, Spikeweeds are always in Flower Pots in the Zen Garden.
 * This is probably because a Spikeweed would be useless in a Flower Pot, as zombies wouldn't walk over it, but they don't need to attack any zombies in the Zen Garden.
 * The Spikeweed is actually too wide for its Flower Pot, and sticks out over the sides.
 * Spikeweeds have a faster attack rate than other plants.
 * When a Spikeweed is planted in one of the two bottom right squares on Pool and Fog Levels, it will be higher up than other Spikeweeds. This is so you can see them over the level progress bar.
 * It is unknown how a Spikeweed can destroy Zombonis and Catapult Zombies just by popping their tires.
 * The Jack-in-the-Box Zombie, the Zomboni, the Catapult Zombie, the Bungee Zombie, the Gargantuar and the Giga-Gargantuar are the only zombies that can destroy Spikeweeds and Spikerocks.
 * Alone, it takes two Spikeweeds to destroy the regular Zombie.
 * When a Zomboni hits a Spikeweed and then a Squash tries to squash it, the Zomboni will not explode when the Squash squashes it.
 * It is unknown how the Spikeweed can make the Zomboni's ice machine or the Catapult Zombie's catapult machine explode by just popping the tires.
 * Spikeweed is one of the twelve plants that appear in the seed selection screen after you get the Grave Buster on the online version, the others are: Ice-shroom, Lily Pad, Potato Mine, Threepeater, Tangle Kelp, Jalapeno, Doom-shroom, Torchwood, Tall-nut, Cactus and Blover.
 * The Spikeweed's flavor text about hockey seems to be in line with its role of destroying Zombonis (a vehicle with a close link to hockey itself).
 * If you look closely, its eyes are red.
 * The Spikeweed and the Spikerock are the only plants that can't be eaten.
 * Sometimes, Spikeweeds can destroy multiple vehicles at once.