You can grow a seedling oak tree indoors, but only for a few years. Oaks have extensive, deep root systems, and will not tolerate being pot-bound for long. A mature oak can reach a height and spread of more than 100 feet and live for hundreds of years, but each one starts life as a tiny seed encased in the hard shell of an acorn. Gather six to eight acorns in the fall for each oak tree you want to grow.
Gather acorns when they ripen in autumn. Pry their little caps off with your fingers. Put them in a plastic bag with a handful of moist sand, if they are red oak acorns. Seal the bag and keep it in the refrigerator for the winter months. If the acorns are from white oak, you can plant them right away.
Prepare a medium-sized, square container in spring. Fill it with moist potting soil, and plant the acorns 1 to 2 inches deep. Put the container in a sunny, warm spot, and keep the soil moist, but not soggy. The viable acorns will sprout in a few weeks.
Thin the seedlings when they reach a height of 3 inches and put out their second set of leaves, leaving the healthiest one.
Keep your oak tree in the same spot in the house for the next few years. Water the tree regularly. No fertiliser is necessary. Transplant the oak into a bigger pot with new soil annually. Trim any long tap roots that emerge from the drainage holes with scissors.
Transplant your indoor oak tree to the landscape after three years. The seedling will need more space than a container offers.
Replacing the container soil annually is important, as it become depleted of nutrients much more quickly than the soil in a garden or yard.