How To Grow Black Walnut Trees From Seed

Growing Black Walnut Trees from seed is an easy activity that one can do in the fall to obtain new trees for little to no cost. You simply need to test the nuts viability be performing the float test, then cold stratify or winter sow the seeds to overcome dormancy. Finally, we can plant the nuts 1-2″ deep and expect them to germinate in the Spring.

I’ve grown and propagated hundreds of trees in my life. And for Black Walnut, this is the best method I’ve found. I’m going to show you exactly what I do from harvest to germination.

Black Walnut trees can be propagated from the nuts that the tree produces. After the walnuts naturally start falling from the tree, you should collect some from the tree itself, not the ground. Then, remove the husk and test the black walnuts viability by seeing if it sinks in water. Plant viable Black Walnuts 1-2″ deep. Trees will sprout in the Spring.^[1][2][3]

If you collect some black walnuts and wish to grow them from seed, you first need to do a test to make sure the nut is a viable seed. Also, Black Walnuts need to undergo cold moist stratification or be winter-sown to germinate.^[1][2][3]

Harvesting Black Walnuts for planting

In late Summer, Black Walnuts will begin to naturally fall from the tree. Sure, you could go grab them off the tree earlier, as they are quite visible by mid-Summer – but the seed (embryo) inside that nut hasn’t fully developed yet! You want to leave the nuts on the tree as long as possible, and only begin harvesting once the nuts naturally fall from the tree. Doing this ensures that the embryo had all the time it needed to fully develop^[4].

So, although you may be tempted to harvest the nuts early – don’t! Just have patience.

Also, you should plan on gathering twice as many walnuts as you want trees. The germination rate can be anywhere from 40-90%, so it’s better to have more to plant.

Removing the husk

Next we need to remove the husk. There are many methods for doing this – some easy, some challenging. If you are just trying to grow a handful of trees though, a simple chef’s knife or hunting knife will suffice. Also – wearing some protective gloves will keep your hands clean. This is optional, but you should know that the husk will turn your hands yellow to brown!

If you leave the walnut to sit in it’s husk for a while (away from squirrels), the husk will soften and begin to turn black. This makes it easier to remove. But, follow the steps below to remove the husk.

1. Place your freshly harvested walnuts on a cutting board or piece of scrap wood.
2. Using a large knife, slice into the husk until you hit the hard wall of the nut shell.
3. Carefully (keeping your other hand out of the way of the knife) roll the nut forward, applying gentle pressure against the shell of the nut.
4. Twist the knife (pushing blade away from your other hand) or pull apart the husk, revealing the nut
5. Rinse and soak the nut in water several times to remove most of the dye (optional)
6. Float test the nut for viability.

If you leave the walnuts in your garage

Testing Black Walnut seed viability

Now, just because the husk has been removed and the nut has fallen from the tree doesn’t mean the embryo inside the shell is viable to germinate. Unfortunately insects can burrow into the the husk and nut, eating the embryo via tiny holes. Also, sometimes a tree may ‘abort’ a nut (often in times of stress or drought), or the embryo can not fully form.

When any of these above scenarios happen, it usually results in air pockets inside the shell. And it is because of these air pockets that we can test the viability of the nut by trying to float it in water^[5]. This test really works, and there is scientific research to back it up. If you are curious for a more detailed explanation, see my write up of the ‘float test’.

But to test the viability of the Black Walnuts, simply float them in water for at least sixty seconds. Nuts that sink are viable, while those that float may not be. If you want to be completely sure, you can leave the walnuts in the water for 12-24 hours and then discard any floating or suspended nuts.

Storing walnuts before planting

If you wish to wait on planting your walnuts until Winter, then you should take care to store them properly. After the float test, dry off the nuts and place them in a sealed plastic container in the refrigerator. Nuts that are allowed to sit out in the open air will dry out. And thus the embryo inside will die, and the nut will no longer be viable.

Direct sowing Black Walnuts

At this point, you know you have viable nuts (haha), you can plant them in a suitable location (see here for growing conditions). But just plant the nut about 2″ deep in the soil. Now, you aren’t quite finished yet, as you will need to protect it from squirrels and rodents digging up the nut.

To keep squirrels from digging up walnuts you planted, place a piece of 12″x12″ chicken wire over the place you planted the nut. To keep it in place, place a rock or heavy weight on top. This will frustrate and prevent any rodent or squirrel from treating themselves to your soon-to-be tree.

If you wish to start your walnuts in pots though, continue to the next section.

Cold Stratify walnuts for germination

Black Walnuts have a dormancy mechanism preventing premature germination. To overcome this, we must either cold stratify or winter sow the seed.

Cold stratifying Black Walnuts in the refrigerator

To cold stratify and store Black Walnuts prior to planting, get a large 1-gallon zip-lock bag and some sand or vermiculite. Mix the sand/vermiculite with water so that it is damp. The amount of dampness is that if you squeeze a handful only a couple of drops should drip from your hand.

Then, place your Black Walnuts into the center of the mixture, and place into the zip-lock bag. Store this in the fridge until you are ready to plant.

How to plant and germinate Black Walnuts

This section is applicable if you plant to Winter Sow (my preferred method) the walnuts or for planting after you have cold stratified in the fridge. But I will describe it in terms of winter sowing.

Since Black Walnuts need a cold treatment, winter-sowing is the easiest method. Just let mother nature do the work for you.

1. Fill a container with moist potting soil. The container should be at least 6″ deep (9-14″ tree pots are better).
2. Planting Depth – Plant Black Walnuts 1-2″ deep into the soil (2.5-5 cm)
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3. Set the container outside in a location that receives morning sun and afternoon shade. Alternatively, you can place the container in an unheated garden shed or garage. This will raise the germination rate in zones 3-6. Black Walnuts are resistant to freezing, as they the shell that acts as insulation, however, they just need to be in cold weather (~40F). They don’t need the freeze/thaw cycles.
4. Protect the container from squirrels and rodents. Hardware cloth, screens, or something similar with a rock on top works great.
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5. Germination will occur in roughly the middle of Spring, once temperatures begin warming up overnight

Video guide to growing Black Walnut Trees from seed:

Below is a short video on how to grow a Black Walnut tree from Seed. This video contains all information you need to successfully germinate the nuts.