No Power Cells are required to "pull" these grass plants that can be found "growing" (while not spawning, but in reality already being part of the template worlds) on blocks of green Grass in Grassland, Woodlands, Forests, Swamplands, valleys between Mountains or on Savannah Grass in Savannah biomes.
The same units of Tallgrass can then be placed again (take care to not place them "into" each other or one of the two will vanish) and pulled once more however often you like and they will still randomly "drop" Wheat Seeds.
Seeds cannot be consumed by player characters or Pets directly.
You can grow Crops like Wheat from Wheat Seeds on tilled blocks of Dirt, green Grass and/or Mud. First place such natural blocks over a body of Water or Mineral Water, 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 pools of Bog Water. In these cases, Seeds will stay "fallow" and won't grow (they can be picked up again though).
Next craft a Plow and use it on the solid blocks to till them; they will turn into "tilled land". Then place Seeds on the tilled land (just like you'd place any block). You can, but you do not need to fertilize Seeds in order to make your Crops grow faster.
Wait a bit until the Crops are ripe to receive the best harvest. Wheat needs approx. 50 minutes (real-life-time) to grow from seeds into ripe plants, even if you're offline. Lettuce needs about 60 minutes, Turnips not much longer (ca. 61 minutes), Horned Melons need ca. 90 minutes until they're ripe.
Crops can be harvested by being "pulled" with the gauntlet and left mouse button (by default) just like any other type of block, item, plant or liquid. If Crops stay "ripe" for 24 RL hours, they will turn into "grown" Crops. The harvest will become a little less then, but Crops won't wither.