How can black walnuts be turned into new trees?
Spread the black walnut love by planting the nuts directly into the ground in October or November. Plant them with husks—the green outer shell—intact, 4–5 cm deep in moist but well-drained soil. Or, store them in the fridge for four to six months (any longer and they’ll lose their viability) then plant them in the spring. Before storage, remove the husks by tapping them with a hammer. Wear gloves for this since they leak a blackish-brown juice.
Trees can also be started in pots to transplant in the spring. In this case, plant the nuts with their husks off. Make a hole in the soil only as deep as the nut is thick, push it down to secure it, then cover with a thin layer of soil. Water, seal the pot with plastic wrap to keep in moisture, and place in a sunny window. Then wait. Seedlings may not form for six months. When the plant starts to grow, remove the plastic, and water twice a week. In another six months, the tree will be ready to go in the ground.
Keep in mind that in Canada, black walnut trees mostly grow in southern central Ontario, and the farther north you go, the less likely they are to flourish because of a shorter growing season. Also, black walnut trees are messy as leaves and nuts are hard to rake up. Furthermore, fallen leaves and roots leach a substance called juglone, which inhibits the growth of many other plants. So don’t put this tree beside a vegetable garden or flowerbed.