Crisphead Lettuce is a Crop that grows in the wild in many surface biomes, can be harvested, processed into Seeds, planted und such multiplied.
Lettuce can be fed to Pets (only few perfer Crisphead Lettuce as their favorite type of fodder though), this Crop can also be consumed by player characters directly for a small buff, and it can be cooked into several Food types that grant significant advantages to player characters and are the best fodder for many Pets.
Where to find
Crisphead Lettuce can occasionally be found on the ground of Forests, Tundras, sometimes also in Swamplands and other Biomes. Lettuce usually grows on blocks of green Grass, but occasionally on Dead Grass too.
Right after world generation, Crisphead Lettuce is very rare, but the longer you play on a game-world, the more Lettuces will show up. Like with the other 2 wild Crops (Turnips in Swamplands, Tundras etc. and Horned Melons only in Jungles), more and more Lettuce heads will slowly spawn on game worlds where players are active.
Staying close to a suitable biome might raise the chances for Lettuces to spawn there.
The "Pro" world option "more regrowth" should make more Lettuce heads spawn in suitable Biomes on the surface of the game world even faster.
When Crops like Crisphead Lettuces are captured with Capture Blocks, the Blueprint and its building kit will include Seeds of the according Crops (Lettuce Seeds) instead. This applies to Crops found in the wild as well as to player-grown Crops on tilled land.
This means that you can only buy Seeds of Crops (also Mushroom Spores) as a content of building kits for customizable Blueprints - to be paid with ingame Coins that can be bought for real money via Steam Wallet in the ingame Store.
How to use
Crisphead Lettuce can be consumed raw (from the inventory by dragging it over the model of the player character on the right side or from any quickslot by right-click) and will then provide 100 additional maximum Health Points for 6 minutes, but will not even heal player characters. So this is not the most efficient way to use Lettuce.
Instead, Crisphead Lettuce is a valued ingredient for many types of Food that can be made in a Cooking Station. Food provides player characters with a wide range of buffs (positive effects). Plus Lettuce can be used to cook many favorite types of fodder for most types of Pets too.
The Cooking Station only provides 4 cooking recipes for the aforementioned 4 types of Foodstuff, but by choosing different ingredients, you can cook up to 36 types of Food with different positive effects when consumed (either use right-click after putting the Food into any slot in your quickbar and selecting this quickslot, or drag a stack of Food from your inventory over your character's portrait on the right side with the left mouse button).
How to multiply
1 Crisphead Lettuce can be processed for 2 Lettuce Seeds in a Processor. Then these Seeds can be planted on tilled soil so that they can grow into Lettuce Crops. In this way Lettuce can be multiplied.
No crafting recipes needs to be unlocked in order to process Lettuce into Seeds. Simply carry Crisphead Lettuce with you in your inventory or quickbar and activate a Processor in the game world either with right-click or by pressing "f" (as the default key) while pointing your cursor at the Processor.
Either place such natural blocks over a body of Water (or Mineral Water) before plowing the solid blocks, or alternatively place these liquids directly adjacent to each block of Dirt, Grass or Mud (like directly below for example, or at least corner to corner).
This can even be done underground in complete darkness and/or in a building, but not at too high altitudes, not in too cold nor too hot Biomes/layers, and not too close to Swamplands or larger pools of Bog Water. Under these unsuitable conditions, Seeds will stay "fallow" and won't grow (they can be picked up again though). Some biomes are simply not suitable to grow Crops for unknown reasons - in this case, you might want to try growing the Crops in the underground or higher up, which often works well.
Craft a Plow, equip it and use it like you use any tool by (holding) left click and pointing your cursor at the solid blocks of either Dirt, green Grass or Mud to till them; they will turn into "tilled land". Then place Crisphead Lettuce Seeds on the tilled land with right-click from your quickbar, just like you'd place any block or object.
You can, but you do not need to fertilize the Seeds in order to make your Crops grow faster. For this, simply place Pigsy Droppings (a pet-harvest from Pigsies, Night Pigsies or Night Hoglets) on the Lettuce Seeds directly after placing the Seeds, which will make them turn into Seedlings (the first growth stage) right away.
Or you can alternatively wait for ca. 10 minutes and then fertilize the naturally grown Seedlings in order to make the Lettuce grow within 40 minutes from then on instead of 50 minutes. You can only fertilize each Crop once, only either Seed or Seedling.
Wait a bit until the Crops are ripe to receive the best harvest. Lettuce requires about 60 minutes to be grown from Seeds into ripe Lettuce Plants in total, but only 50 minutes when fertilized. Neither fertilizer, the type of soil, the type of moisture nor the circumstances of the environment will make any difference for the harvest.
If Crops stay "ripe" for 24 RL hours, they will turn into "grown" Crops. The harvest will become a little less from then on (only 1 Lettuce instead of occasionally 2 per harvest), but the Crops won't ever wither.
Crops can be harvested by being "pulled" with the ArcTek Gauntlet without even requiring any Mining Cell. Use the left mouse button (by default) just like on any other type of block, item, plant or liquid to pick the Lettuce heads.
Please refer to the article Farming if you want to know more about how to grow Crops and please read the article Food if you want to learn more about how to cook up to 36 types of buff-granting Food by making use of the 4 types of Crops that you can plant.