Wall-nut

The Wall-nut is a defensive plant that acts as a shield for your plants. Place a Wall-nut in front of your plants to block the zombies. Vaulting Zombies can jump over it but they cannot jump over a Tall-nut. It is named after the the edible seed walnut, specifically the Juglans regia. Acts like a stalling plant that makes zombies eat it to waste time. It is obtained after beating level 1-3. The Tall-nut is easy to tell that it is tougher than the Wall-nut because it's taller.

Overview
Absorbs 72 bites. Its appearance changes at 24 bites and 48 bites before finally being swallowed at 72 bites.

Suburban Almanac Entry
Wall-nut

Wall-nuts have hard shells which you can use to protect your other plants.

Toughness: high

"People wonder how I feel about getting constantly chewed on by zombies," says Wall-nut. "What they don't realize is that with my limited senses all I can feel is a kind of tingling, like a relaxing back rub."

Cost: 50

Recharge: slow

Standard Levels
Most plants are very vulnerable to being eaten by zombies, so you may need an extra line of defense. Wall-nuts are cheap and give you the most delay for their cost than any other plant (except for Puff-shrooms, Sea-shrooms, and their Imitater variants, as they are free), so they can make a good early defense; especially when combined with a Spikeweed. Later, when you can afford it, you'll want to purchase Wall-nut First Aid from, as this will allow you to replace Wall-nuts that have been damaged without having to dig them up first. When a Wall-nut starts to look sad, it is about to die, so try to replace them quickly at that point. Note that Pogo Zombies, Pole Vaulting Zombies, and Dolphin Rider Zombies can easily get past Wall-nuts, and they will only slow down Gargantuars for as long as it takes for them to smash the Wall-nut. The Wall-nut is also useful against Snorkel Zombies, as when planted on Lily Pads in the Snorkel Zombie's path the Snorkel Zombie will be forced to raise its head from the water, making it vulnerable to attack.

Wall-nut Bowling and Wall-nut Bowling 2 Mini-games
Wall-nuts are your standard ammo in Wall-nut Bowling. They will take out normal Zombies, Pole Vaulting Zombies, Dancing Zombies, and Backup Dancers in one hit, Conehead Zombies and Newspaper Zombies in two, and Buckethead Zombies in three, and Screen Door Zombies in four. After striking any zombie, the Wall-nut will bounce off at an angle, possibly hitting more Zombies before it rolls off the screen. It will also only bounce off towards the right as it does not make sense for it to go backwards. Try to hit more than one zombie with each Wall-nut, as on the iPhone version you will get the Roll Some Heads achevement, each additional zombie yields more coins (0 for the first, 1 for the second, 2 for the third, 3 for the fourth, and a gold coin for the fifth or any other zombies past it), and Screen Door Zombies and Newspaper Zombies only take one hit when hit at an angle. Also, remember that the Wall-nut doesn't have to go directly at a Pole Vaulting Zombie to make it jump - it just has to be near enough. Be ready with your nut, holding it in the most forward space (behind the red line), then, when the Wall-nut's picture of where it will be placed appears over the zombie, release. It also doesn't richochet (if you're using normal nuts, that is.) There are two Wall-nut variations found in these Mini-games:

Explode-o-nut
The Explode-o-nut is found only in Wall-nut Bowling, Wall-nut Bowling 2, and Co-Op Wall-nut Bowling. It cannot be bought or planted outside the Mini-game. It is a red Wall-nut which, upon hitting a zombie, creates an explosion the size of that from a Cherry Bomb. It should be used where there is a cluster of stronger zombies. Rather than rolling it at the zombies, you can make better use of it by waiting until the zombies cross the line and dropping it in the middle of them.

Giant Wall-nut
The Giant Wall-nut is found in Wall-nut Bowling 2. When used, it rolls down a row and squashes all the zombies, acting as a sort of Jalapeno and Squash, because it hits all zombie in a lane and squashes them. Fortunately, it's too high to be vaulted by a Pole Vaulting Zombie. It does not bounce off zombies, but runs them over. However, you do not get any coins from the combos dealt from a Giant Wall-nut. You also can't get the Roll Some Heads Achievements.

ZomBotany and ZomBotany 2 Mini-games
The Wall-nut Zombies in the ZomBotany mini-games are very resistant to damage, taking about the same amount of damage as a Zomboni or Zombie Yeti (3 more damage, Wall-nut is 72 damage, zombie is 10). The best plan is to stop them with Wall-nuts of your own while hitting them with as much damage as you can. The Wall-nuts also serve to stop Tall-nut Zombies and the peas of Peashooter and Gatling Pea Zombies, so they are one of the best plants to use.

Beghouled and Beghouled Twist Mini-games
It is difficult to control when and where you will get Wall-nuts in this game, so it's almost pointless to upgrade them to Tall-nuts. If you do manage to get three or more on the front, try to leave them there and only complete matches in the rear lanes (especially Wall-nuts in any other column). It is a good idea to upgrade them eventually, but if you decide to it is best to wait until the other plants have been upgraded.

Totally Nuts I, Zombie level
Ladder Zombies are pretty much required here unless you luck out and get a lane with no offensive plants at all. Ladder Zombies can survive many hits, so they are generally fine for any lane with only a single regular Peashooter or Fume-shroom in the second or third column from the left. If there is more than one attacking plant of any kind, you may need to follow the Ladder Zombie up with a Buckethead Zombie, and if there are Snow Peas you may need a second Ladder Zombie. Regular Zombies are almost useless on this level, except to follow a Ladder Zombie if it dies right before eating the Brains. The Fume-shrooms can directly attack them. See more in this level.

Portal Combat Mini-game
Use the Wall-nuts you get here to protect particularly vulnerable Portals (e.g. ones that lead straight to the back behind all your plants) from the the front or from behind. Otherwise, just use them to block the zombies in particularly crucial locations. However, make sure that Balloon Zombies don't end up floating over them.

Trivia

 * The Wall-nut freezes while zombies are chewing on it, just like the Tall-nut (however, in DS version it's still moving).
 * This freezing effect is also applied to the Lily Pad, the Plantern, the Pumpkin, and the Flower Pot.
 * If you notice, these plants that freeze when being bitten are plants without offensive capabilities.
 * Although the Wall-nut is named after the walnut, it is also resemble of a coconut because of its hard shell and its ability to roll in Wall-nut Bowling.
 * The Wall-nut is one of five plants that will slowly degrade as they are eaten/damaged. The others are the Pumpkin, Tall-nut, Garlic and Spikerock.
 * The Wall-nut, the Magnet-shroom, the Threepeater and Squash are the only plants that are seen smaller other than on the lawn. The Wall-nut and is seen as small as Crazy Dave's hand when he talks to you before playing Wall-nut Bowling (Level 1-5); the Magnet-shroom, the Threepeater and the Squash are seen on Crazy Dave when he tells you that you have to buy the full version when you're playing Plants vs. Zombies trial after completing level 3-4.
 * In the Plants vs Zombies website, when on the Zombatar tab, a Wall-nut with a red hair can be seen in a corner of the screen.
 * The Wall-nut, Cob Cannon, Starfruit, and the Gatling Pea are the only plants with mini-games dedicated to them.
 * Wall-nut has two Mini-games related to him: Wall-nut Bowling and Wall-nut Bowling 2.
 * Wall-nut originaly had another Mini-game like Seeing Stars, it still exists, but only available with cheats.
 * The Wall-nut has the 2nd most variations: regular, Explode-o-nut, Giant Wall-nut, Tall-nut, Imitater, Wall-nut Zombie & Tall-nut Zombie.
 * The Wall-nut and the Zombie (and its variants) both have the same eye design. The bigger eye is just flipped over.
 * The Wall-nut is grown in the Zen Garden with no roots.
 * If you look closely, the Wall-nut's mouth moves as if it is saying something.
 * In Wall-nut Bowling and Wall-nut Bowling 2, Pole Vaulting Zombies will jump quite earlier before the Wall-nut rolls 1 square in front of it.
 * According to the Tree of Wisdom, Wall-nut and Chomper were once roomates in college, which is why they work well together.
 * Occasionally, the Wall-nut will end up blinking while a zombie is eating it, due to the freezing of its animation.
 * Sometimes, the Wall-nut will squint one of its eyes.
 * The Wall-nut is one of 5 plants whose purpose is to be chewed on. The other 5 are the Tall-nut, Pumpkin, Garlic, and the Hypno-Shroom.
 * These four are defensive plants.
 * You need him for the achievement Nom Nom Nom.
 * Wall-nut is hollow on the inside.
 * The Sunflower and Wall-nut seem to both "dance".