Spikerock

Spikerock is the upgrade of Spikeweed, and is purchased from Crazy Dave's Twiddydinkies for $7,500. It is a passive attacking plant, dealing high damage to any zombies that walk on it. It costs 125 sun to upgrade a Spikeweed to a Spikerock, for a total cost of 225 sun. It usually deals ten attacks in groups of two, (each attack doing one damage) for every normal speed zombie that passes unimpeded over it (exceptions include zombies that come in a group, when one zombie gets on just after the Spikerock fires). Spikerocks will pop tires, on up to nine Vehicles (Zombonis and Catapult Zombies) before dying, with one of its large spikes to breaking off with every three vehicles. When a Gargantuar attacks it, it will have the same effect as when vehicles roll over it, without the Gargantuar dying. Since the Spikerock attacks from below, it bypasses shields and fast attacks zombies.

Note: Spikerocks cannot be planted on Lily Pad or Flower Pot, like Spikeweed, either.

Suburban Almanac Entry
Spikerock

Spikerocks pop multiple tires and damage zombies that walk over it.

Must be planted on Spikeweeds

Spikerock just got back from a trip to Europe. He had a great time, met some wonderful people, really broadened his horizons. He never knew they made museums so big, or put so many paintings in them. That was a big surprise for him.

Cost: 125

Recharge: very slow

Overview
The Spikerock prior to Plants vs. Zombies 2: It's About Time absorbs nine smashes and its appearance changes at three smashes and six smashes before finally being dead at nine smashes. It will damage zombies at ten normal damage shots per a regular zombie's patch speed. It will automatically kill Zomboni and Catapult Zombie by popping the tires. As of Plants vs. Zombies 2: It's About Time it will destroy 3 rolling objects before being destroyed (at being rolled on for the third time).

Strategies
Use the Snow Pea, Winter Melon or Ice-shroom to slow the zombies, so they spend more time being attacked by the Spikerock. A Snow Pea and a Spikerock is particularly cost effective, but if Winter Melons are used, all zombies get slowed, you can also use the Kernel-pult as if it uses a butter and a zombie is standing on a Spikerock, it will continue to take damage.

Plant the Spikerock in front of a Wall-nut, Tall-nut, or Pumpkin. Most zombies do not attack it, and are continuously damaged as they try to break down the defensive plant.

The Spikerock is uniquely capable of withstanding multiple strikes from Gargantuars. This considerably slows Gargantuars and allows extra time for your other defenses to attack, since, unlike other zombies, Gargantuars will stop to destroy the Spikerocks.

The Spikerock can also damage Newspaper Zombies, Screen Door Zombies and Ladder Zombies without destroying the shield before.

Bobsled Bonanza Mini-game
As it can pop multiple tires, the Spikerock is an incredibly useful plant to use on this level. It is a good idea to plant a column of Spikeweeds at the edge of the ice to deal with Zombonis, but they should be upgraded to Spikerocks as soon as possible. To deal with the Zombie Bobsled Teams, there should be an additional Spikeweed behind the Spikerock (as the zombies can only take one normal damage shot after passing over the Spikerock, although when first setting up it is best to plant three).

Survival Mode
Though useful on the early waves, Spikerock is not recommended for Survival: Endless due to overlapping Zombonis, Catapult Zombies, and assorted Gargantuars. Often, a Spikerock may be killed shortly after it was placed down. However, Spikerock is ideal for any survival level, easy or hard. The ability to kill multiple Zombonis, that if left alone, will crush your setup, is a superb one by any fact. It can also save your offensive plants some time, as one Spikerock can kill a regular zombie without help.

Trivia

 * Jack-in-the-Box Zombies, Zombonis, Catapult Zombies, Jalapeno Zombies, Gargantuars and Giga-gargantuars are the only zombies capable of damaging Spikeweeds and Spikerocks.
 * When a Spikerock is planted in one of the two bottom right squares, it will be higher up than other Spikerocks. This is so you can see them over the level progress bar.
 * The Spikerock is the most durable plant in the game because it can withstand nine Gargantuar's smashes and nine tire pops of the Zomboni and Catapult Zombie. Despite its resilience, it still only takes take one Jack-in-the-Box Zombie or Jalapeno Zombie explosion or Bungee Zombie grab to destroy a healthy Spikerock. It seems highly unusual that a Jalapeno Zombie can destroy something biologically rock and its melting point would be massive and take temperatures vastly beyond the output of a Jalapeno Zombie, and the fact rock is inflammable makes the very brief blast of the Jalapeno Zombie seem even less able to destroy or melt rock.
 * Biologically, the Spikerock is not a plant; it is a rock.
 * The Spikerock can still harm Bungee Zombies even though they are in the air.
 * The Spikerock is one of four plants that have names which don't involve plants with the others being the Grave Buster, the Gold Magnet and the Chomper.
 * This is one of only two plants that change appearance but cannot be healed with Wall-nut First Aid, the other being Garlic.
 * It is unknown how the Spikerock can make the Catapult Zombie's catapult machine or zomboni's ice machine explode by just popping the tires.
 * The Spikerock and the Squash are the only plants that can survive Gargantuar smashes and a vehicle.
 * The Spikerock is the only upgrade plant that can't be eaten.
 * On the iPod version, spikes will not fall off Spikerocks.
 * The Spikeweed, Spikerock, Potato Mine, Grave Buster, Tangle Kelp, Sea-shroom and Flower Pot are the only plants that cannot be planted on a Lily Pad.
 * The Spikeweed, Spikerock, Cattail, Grave Buster, Tangle Kelp, Sea-shroom and Lily Pad are the only plants that cannot be planted on a Flower Pot.