Sun

Sun is the resource player needs to plant their Plants, being essential for use in creating defenses against zombies.

How to Use It
Each plant costs a certain amount of sun to plant, limiting the number of plants you can place on the lawn at a time. Your planting is also limited by the recharge or "cooldown" rate of the seed packets. Also, upgrade plants cannot be planted unless the plant of which they are an upgrade of have already been planted, even if you have enough sun for them. The only plants that do not cost sun to plant are the Puff-shroom, its aquatic cousin the Sea-shroom, and Imitater versions of them.

How to Obtain It
Sun is obtained from Sun-producing Plants, in addition to the player starting every ordinary level with 50 Sun. Sun also falls from the sky in the daytime areas Day, Pool, and Roof. During the Night and Fog levels, Sun-producers are the only way to obtain Sun, so some of these plants must be planted to obtain more than the starting 50 sun. Sunflowers produce 25 Sun, Twin Sunflowers produce two 25-value sun pieces, and Sun-shrooms produce 15 sun until they grow, after which they produce 25 sun.

Trivia

 * The maximum amount of sun you can get in Plants vs. Zombies is 9990.
 * This, along with the 15 sun increments from small Sun-shroom, is the only way to get sun that is not in multiples of 25.
 * On the iPhone/iPod Touch versions of the game, there is an Achievement called Sunny Days unlocked by getting 8000 sun.
 * Survival: Endless is the only level where the cost of plants rises (the cost of Upgrade Plants rising for every one of each type currently planted on the lawn).