When choosing the best place to plant a northern california black walnut, it is important to consider two things: the amount of sunlight, and any surrounding planting. When it comes to light, northern california black walnut can cope with part or dappled shade but will grow and fruit best when planted in full sun. East-facing aspects (or west, if in the southern hemisphere) are best avoided in areas that are prone to late frosts. In the spring, young shoots can be damaged if exposed to morning sunlight after a frosty night.
Northern california black walnut is classed as allelopathic trees, as it releases chemicals that have some type of effect on another plant. The fallen leaves and husks contain a chemical called juglone, which acts as a natural herbicide and prevents competing vegetation from growing. Juglone levels are highest within the drip line of the tree (the outermost circumference of the tree's canopy, from which water drips onto the ground), so anything growing in this area is likely to yellow and wilt. Apples, tomatoes, pines, and birches are most susceptible to juglone poisoning.
Northern california black walnut can be planted at any time from winter to spring into any rich, well-drained soil type. Dig a hole three times wider and to the same depth as the pot. Loosen the soil around the sides and base of the hole with a fork. Remove the tree from its pot and slightly loosen the root ball with your fingers to tease out the root system and encourage it to grow out from the planting hole. Place the tree into the hole so that the top of the root ball is at the same level as the soil surface. Turn it until you are happy with the appearance and direction the branches are going to grow in.
Backfill the hole, firming the soil in gently as you go. Water well and add a layer of mulch 5 to 8 cm deep. Do not mulch too close to the stem, as this can lead to rotting. Larger, top-heavy trees can be staked to prevent wind rock. Hammer in a stake at a 45-degree angle to avoid damage to the root ball, and attach the tree to the stake with a tree tie.
Although not recommended for good nut crops, northern california black walnut can be grown in containers. It is planted in the same way as a ground-grown tree: into a tree or shrub compost with sharp sand incorporated to assist with drainage. As before, firm soil gently and water well. Mulch can be added to the container if required. Container-grown plants should always be raised slightly from the ground to allow water to drain freely from the holes in the base of the pot.