Spikerock

Spikerock is a passive attacking plant with extrordinarily high health (multiple times that of a tall-nut), dealing high damage to any zombies that dare to tread on it.

Usage
It costs 125 Sun to upgrade spikeweed to spikerock, for a total cost of 225 Sun. It deals five attacks for every normal speed zombie that passes [unimpeded] over it. It deals group damage, damaging ALL zombies that stand on it at any given time

Strategy
Slow zombies so they spend more time being attacked by the spikerock, using snowpea, winter melon or ice-shroom. Snowpea and spikerock is particularly cost effective.

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

The Spikerock is (uniquely) capable of withstanding multiple strikes from Gargantuar. This considerably slows Gargantuar and allows extra time for your other defences to attack.

Spikerocks will pop tyres on three ice-layers (spikeweed only lasts for one).

Spikerock is also an excellent counter against Zombonis if no other recourse is available.

NB. Jack-in-the-box (when exploding) and Gargantuar are the only zombies capable of damaging plants like spikeweed.