Growing Black Walnut Trees

A mature Black Walnut at our farm.

I love working with Black Walnut wood. Whether I am creating decorative forms, cutting boards for the kitchen, furniture, or fruit and salad bowls for daily use, the rich chocolate tones and striking grain patterns of American Black Walnut (Juglans nigra) rarely disappoint.

Local homeowners and tree services know that I enjoy working with this wood and are happy to alert me when one must be removed because it threatens a structure due to its age, storm or insect damage. I get wood which would otherwise go to waste and the homeowner gets a bowl or board for their kitchen. I marvel at a few extremely large species on our farm and wonder how many years ago the nuts from which these giants grew fell to the ground and were overlooked (or buried and forgotten?) by a squirrel.

I regularly harvest and germinate a few nuts from our trees. I plant some on our property and give many away to friends and neighbors. I like to think that someone might enjoy these in 50+ years as I do now. (Perhaps they will be grateful for my sustainability efforts!)

If you are fortunate enough to have access to some walnuts when they fall, here are the steps which I follow to prepare the seeds for germination. Unlike many garden seeds, walnuts need a period of cold conditioning (also known as cold stratification) for successful germination.

September harvest of walnuts, husks intact.

Step 1: Collect and Prepare Seeds

1. Harvest fresh nuts in the fall after they drop naturally from the tree.

2. Remove the husks if they’re still attached:

   • Use gloves (the husks will stain hands, clothes, pretty much anything!).

   • Let them soak in water for a few days if husks are difficult to remove.

3. Rinse thoroughly and discard any that float in water—they’re likely non-viable.

4. Air-dry them for a few days in a shaded, ventilated area.

Step 2: Cold Stratification (Simulating Winter)

1. Moisten some sphagnum moss, peat moss, or sand (just damp, not soggy).

2. Mix the nuts with the moist medium in a plastic bag or container with small ventilation holes.

3. Label the container with the date.

4. Place in refrigerator at 34–41°F (1–5°C) for 90 to 120 days.

   • Check monthly to ensure the medium stays moist and there’s no mold (remove any moldy nuts).

Step 3: Germination and Planting

1. After stratification, check for sprouted roots (especially if over 3 months in stratification).

2. Plant immediately: I plant them 1–2 inches deep, root side down in narrow, deep plastic pots since the nuts will initially produce one main tap root and I want it to have some room to grow.

3. Water regularly and protect from animals. Squirrels WILL find the nuts and excavate them for you.

4. Transplant seedlings to permanent spots once they’re 1–2 feet tall and after the last frost. I like to dig a hole about twice as deep as the pot - again, to accommodate that important tap root. Take care not to break the root during transplanting.

5. I like to apply some mulch around the seedling to discourage weeds, and protect the seedling from deer with a few metal stakes and a ring of chicken wire. If the seedling makes it through its first Winter, it may be necessary to enlarge the chicken wire as the tree grows. We are plagued by deer in our area, so I leave this protection up for a few years.

   
   

   

   One of our juvenile Black Walnut trees, now about 30' tall, planted roughly 15 years ago.

   
   

Important Note

• Black Walnut Trees inhibit the growth of many other plants through a natural chemical process known as allelopathy. This is a biological phenomenon where the Walnut tree releases chemicals - primarily through its root system - that affect the growth, survival, or reproduction of neighboring plants. The primary compound responsible is juglone (5-hydroxy-1,4-naphthoquinone). Juglone is toxic to many plants, especially those not adapted to it. It is found in all parts of the Black Walnut tree and can affect any plant under the tree's (eventual) canopy. Planting your seedlings near any other species may compromise those plants. Similarly, it is best not to not plant another species where a Black Walnut once stood since the juglone remains in the soil. I learned this the hard way. Also, do not use a Black Walnut's shavings, bark, chips, or leaf debris - all of which will contain the juglone - as garden compost.