Crop

Two standard Crops with a Cross Breeding Crop in-between. On right, a Crop with Dandelions growing.

The Crop is used for holding plants and growing seeds. They are also necessary for Cross Breeding. They can only be placed on tilled dirt.

To place a Crop, right click on tilled dirt. A Seed Bag or plant can now be placed on the Crop by right clicking on the newly placed Crop. For Cross Breeding, right click to place another Crop on the first one. However, Cross Breeding only works if the Cross Breeding crop is in-between two other plants.

Once a plant is fully mature it can be right-clicked to be harvested without destroying the plant. Left clicking the plant will break the plant, and has a chance to drop a Seed Bag. The drop chance for seeds and the items you get from the plant is based on its stats.

Every plant has a growth, gain, and resist statistic. Each having their own pros and cons.

Growth

Pro: The higher the Growth statistic of a plant, the faster it grows.
Con: The higher the Growth statistic of a plant, the higher the chance of weeds spawning on nearby Crops.

Note: At Growth stat 24 and higher, the plant begins behaving like weeds, destroying nearby crops. Therefore, a recommended ideal Growth stat would be 20-21, to give a reasonable comfort zone for cross-breeding.

Gain

Pro: The higher the Gain statistic of a plant, the better the drop chance of harvests becomes.
Con: The higher the Gain statistic of a plant, the lower the chances of dropping Seed Bags.

Resist

Pro: The higher the Resist statistic of a plant, the more resistant it is to weeds and being trampled, as well as greatly increasing the chance of the plant dropping at least one Seed Bag.
Con: The higher the Resist statistic of a plant, the slower it will cross-breed with other plants.

Note: Crops can still be trampled while sneaking/crouching.

Since Tekkit 3.1.3,crops can no longer be trampled.