Although not true of all types of grapefruit, most types will grow true from germinated seeds. Some varieties of grapefruit in some places, however, may not live as long as grapefruit trees grafted to disease resistant rootstocks. There are a variety of well documented techniques for getting a grapefruit seed to germinate. However, once germinated, planting the seedlings in a pot or greenhouse is not difficult.
Expose your germinated seedlings to about an hour of sun once you see two leaves growing from the young grapefruit plants.
Increase the seedling's exposure to sun by about an hour per day until it can tolerate full sun.
Fill your pot with well draining potting soil once the seedling can tolerate full sun and does not require the humidity tent.
Remove the germinated seed from its sprouting pot or medium. Do not do this if you germinated the seed in a peat pot.
Dig a hole in the potting soil about the size of your germinated grapefruit's root ball or the size of the peat pot in which you germinated the seed.
Place the tree in the hole and cover the roots or peat pot.
Water your grapefruit tree until water runs from the bottom of the pot to ensure that all of the potting soil is moist.
Place your young grapefruit tree in the sun and keep it moist. Water whenever the top 1/4 inch of soil in the pot feels dry.