Growing a walnut tree from seed requires understanding the tree’s natural cycle for successful germination. Walnuts, whether the common English variety (Juglans regia) or the native Black walnut (Juglans nigra), possess a deep dormancy that must be overcome before the seed can sprout. Propagation involves carefully mimicking the winter conditions the nut would naturally experience on the forest floor. Following specific steps for selection, preparation, and planting increases the chances of transforming a single nut into a long-lived tree.
Selecting and Preparing the Nut for Planting
The journey begins in the fall by selecting a nut that has recently fallen from the tree, indicating it is fully mature. Walnuts are enclosed in a fleshy outer husk, which should be removed immediately after collection, as this hull contains chemicals that inhibit germination and can stain your hands significantly.
After husking, test the nut for viability by placing it in water. Discard any nuts that float, as they likely contain air pockets or shriveled kernels and are not viable. Only keep the nuts that sink to the bottom for planting.
Walnut seeds require stratification, a process that breaks dormancy through a prolonged period of cold, moist conditions lasting 90 to 120 days. This chilling period signals to the embryo that winter has passed and it is safe to begin growth.
Stratification can be natural or artificial. Natural stratification involves planting the viable nuts directly into the ground, approximately two inches deep, in the late fall. For artificial stratification, store the nuts in a refrigerator between 34 and 41 degrees Fahrenheit.
To prepare for artificial stratification, mix the nuts with a moist medium like peat moss or vermiculite in a sealed container. The medium should be damp but not waterlogged, as excessive moisture can lead to mold. Check the nuts periodically throughout the chilling period to ensure the medium remains consistently moist.
Planting the Stratified Seed
The ideal time to plant your stratified walnut seed is in the early spring, after the danger of a hard frost has passed. Planting at this time ensures the seed is ready to germinate once the soil warms slightly, having already satisfied its cold requirement. A location that receives full, direct sunlight for most of the day is necessary for the developing tree’s long-term health and growth.
The soil should be deep, rich, and well-draining, as walnuts develop an extensive taproot and do not tolerate standing water. Plant the seed roughly two to three inches below the soil surface. Some growers recommend placing the nut on its side or with the pointed end facing down, though ensuring it is firmly covered at the correct depth is most important.
If starting the seed in a container, select a deep pot, such as a tree band or nursery container, to accommodate the rapid development of the taproot. A pot depth of at least six inches is recommended to prevent the seedling from becoming root-bound prematurely. Use a standard potting mix composed of compost, soil, and sand, and sow the nut about one to two inches deep.
Nurturing the Young Seedling
Once the seedling emerges, consistent moisture is a priority, especially during the first growing season. Water the young plant regularly, ensuring the soil stays consistently moist but never waterlogged. Establishing a regular watering schedule helps the tree develop a strong root system capable of sustaining it through later life.
Protecting the newly planted nut and emerging shoot from predators is a key challenge. Rodents, particularly squirrels, are highly attracted to the planted nut and will often dig it up, even after the seedling has sprouted. To deter them, cover the planting site with a physical barrier, such as a piece of hardware cloth or chicken wire secured to the ground.
Weed control is also important, as weeds compete with the young tree for water and nutrients. Keep the area immediately surrounding the seedling clear of competitive vegetation to minimize this stress. Applying a two-to-four-inch layer of organic mulch, such as wood chips, helps retain soil moisture and suppress weed growth effectively.
If the walnut was started in a container, the seedling must be transplanted to its permanent outdoor location after its first year of growth. This move is usually performed during the dormant season. When transplanting, be careful not to damage the long taproot, which anchors the tree and accesses deep water sources.