Spikeweed

Spikeweed is an Area of Effect plant that attacks, dealing normal damage to all zombies that walk on it. They can only be planted on the ground (not on Lily Pads or Flower Pots, so that makes them useless for roof levels) and does five peas' worth of damage in the time it takes any normal speed zombie to pass over it (faster zombies, such as the Football Zombie, can take as little as two peas' worth of damage). It will also pop the tires of the first Zomboni or Catapult Zombie that drives over it. Since the Spikeweed attacks from below, it can bypass shields. The player should remember that a Zomboni can kill it. A Spikeweed can be upgraded to Spikerock after purchasing the Spikerock seed packet.

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 favorite 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 (especially in Bobsled Bonanza), 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.

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

 * Somehow, Spikeweeds and Spikerocks damage helmets from headwear zombies, despite them hitting their feet.
 * It and it's upgrade are the only plants that instantly kill some Zombies but only damage others.
 * In the reanim folder, the Spikeweed's name is Caltrop. This may be because the Spikeweed functions like caltrops; it hurts anyone that steps on it and pops tires.
 * Even though Spikeweeds can't be planted in Flower Pots during roof 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, like an armed Potato Mine.
 * Spikeweeds and Spikerocks 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.
 * The Jack-in-the-Box Zombie, the Zomboni, the Catapult Zombie, the Bungee Zombie, the Gargantuar, the Giga-gargantuar, and the Jalapeno Zombie are the only zombies that can destroy Spikeweeds and Spikerocks.
 * Alone, it takes two Spikeweeds to destroy a 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. That is because the Zomboni is already killed after hitting the Spikeweed, so the Squash won't affect 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, although the Spikeweed may degrade their health to zero, if they don't explode, it wouldn't make sense since the zombies can't escape and leave the vehicle on the lawn, the spikes of the Spikeweed and Spikerock may have damaged parts other than the tires, causing the vehicle to explode.
 * Spikeweed is one of the twelve plants that appear in the seed selection screen after the player gets 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) and its main role in the Vasebreaker level Hokey Pokey.
 * If the player looks closely, the Spikeweed's eye pupils are red.
 * The Spikeweed and the Spikerock are the only multi-use plants that can't be eaten.
 * Spikeweed can't be planted on Lily Pads and Flower Pots, possibly because they will not affect zombies there, although Spikeweed can appear on Flower Pots in the Zen Garden.
 * The Spikeweed, Spikerock, Fume-shroom, and Gloom-shroom are the only plants that attack every zombie within their attack range with the same damage to each.
 * It is unknown why in I, Zombie, Crazy Dave made a cardboard Spikeweed when it can't be eaten by zombies, although this may be because it can be destroyed or stolen.
 * The color of Spikeweed's plant part looks like mud.
 * Strangely, its color was changed from brown to green in Plants vs. Zombies 2: It's About Time. This is likely to make it more plant-like.
 * The Spikeweed, Spikerock, Lily Pad, Cattail, Tangle Kelp, and Sea-shroom are the only plants that cannot be planted on a Flower Pot.
 * The Spikeweed, Spikerock, Flower Pot, Tangle Kelp, Sea-shroom, and Potato Mine are the only plants that cannot be planted on a Lily Pad.
 * In Vasebreaker, Spikeweed only appears in Hokey Pokey.