Time to germination: 5 months to a year
Time to harvest: 10 years
Light requirements: Full sun
Soil: Fertile, not sandy
In North America, the most well-known type of walnut tree is definitely the Black Walnut. There are also White Walnuts, English Walnuts, Heartnut Walnuts and Cannonball Walnuts.
All types of walnuts are quite hardy, and actually require a cold winter in order to thrive. So anyone living in warm climates won’t have much success with their own walnut trees. Walnuts will start to produce nuts at around 10 years of age, give full production at 30 and keep on producing for more than 50 years. Depending on the specific type of tree, they can grow up to 100 feet in height.
Many gardeners consider walnuts to be very “messy” trees, much like pecans. They drop their leaves all through the summer, and will kill nearby plants (more on that below).
Starting Your Tree
If you choose to start your walnut tree from a seed, you will want to either plant your seeds where you want your final tree, or transplant it while very small. Walnuts do not do well at all in containers because of deep tap roots and don’t handle transplanting.
You cannot just pick a walnut from the supermarket and plant it in the ground to start your own walnut tree. Nuts intended for eating will not sprout. Contact your local nursery for untreated walnuts for planting. You can plant with or without the husk still on, though taking the husk off will help the plant germinate.
Plant your nuts in the fall, and protect them from squirrels. They need a period of cold before they will sprout. It only needs to be about 3 inches under the soil. They should sprout in 4 to 5 months, or possibly not until the following year.
You can also buy small seedlings, or larger grafted saplings to get a bigger head-start on your nut crops. Grafted saplings have walnut tree branches grafted to the trunk and roots of another type of tree (which is why the survive transplanting better).
One tree is fine on its own, but if you want a group or stand of walnut trees, you need to keep 20 feet or more between them. A single walnut tree can self-fertilize, meaning you will get nuts even with just one tree. You can get a larger harvest of nuts per tree if you have 2 or more though.
Placement of your tree is more important than with most other nut trees because walnut leaves are toxic. The leaves (as well as the roots) give off a substance called juglone, and it will kill any other plants nearby including the grass. So if your plans include having your nut trees within the yard, or overhanging other plants, you’ll have to pick another kind of tree. Also, keep your walnut leaves out of the compost pile.
Unlike annual garden plants, your walnut tree is a more permanent installation. It’s important to take the necessary time to map out the best location for your trees. There should be full sun (remember to plan ahead by at least 10 years), and no solid rock at least 3 under the surface of the soil. Ideally, your soil will be rich and well-drained but not sandy.
Depending on the age and size of the tree, you may not be able to significantly treat diseases or insect infestations on a walnut tree.
Webworms or tent caterpillars can be a problem if there are too many of them on your trees. They build large tents of webbing, that can house hundreds of hungry caterpillars. Cut any branches off with tents and dispose of them carefully. If the problem is severe, spray the tree with BT (Bacillus thuringinsis) a natural bacteria-based pesticide that will attack the caterpillars. Harsher sprays of Carbaryl or Malathion can also kill them.
Full size trees have very long and deep root systems, which usually can protect them from moisture problems on the surface. But after very prolonged periods of drought, your trees might need some watering. You can end up with “burned” walnuts come harvest time if you let your trees get too dry for too long.
Walnut trees should be left to grow naturally without pruning.
Harvest and Storage
If you didn’t already know that early black dye came from Black walnut husks, you’re going to learn after you try to harvest a few of your nuts.
Initially, your tree will produce round green “fruits” that look quite a bit like tennis balls. These are the walnuts. The green outside husk actually has the nut inside of it. To harvest, you have to wait until they are mature enough to drop off of the tree on their own. You don’t pick them. This can make for a bit of a messy and unpredictable nut harvest.
As they ripen, the green husks will come apart and turn black. It’s at this point that they will stain anything they touch, including your hands. Don’t leave your nuts for too long inside the husks at this point. The oils will seep in through the nut shell, and taint the nut meats. Get the nuts out of their husks as soon as they drop off the tree.
Getting the husks off can be a bit of a chore, and some home gardeners even lay out their nuts out on the driveway and drive over them. There are less drastic measures though. Rolling them back and forth on a hard surface (driveway, sidewalk, large stones), with your foot is a more common method. You’ll need to put your weight behind it though. The nuts and husks will stain your work area, so don’t unhusk your walnuts out on the front sidewalk.
If your nuts have ripened enough to be very black on the outside, you may find worms have made a home in them. These are husk fly larvae and they make husking a bit unpleasant but they don’t represent any danger to the hard nuts inside.
Inside the husks, you’ll find a whole walnut in its shell. Wash off the husk remains and keep your harvest somewhere warm and well-ventilated for a few weeks. Warmer temperatures will mean a shorter drying time. You can check for adequate drying by cracking open a nut and testing the little hard divider that runs between the two halves of the nut meat (sometimes called the septum). That piece should be hard and crisp. If its soft, then your nuts aren’t dry enough. Fresher nuts won’t taste the same, though they can be eaten.
After that, you just have to shell them to remove the edible nut meats inside. Dried walnuts still in their shells will last up to a year.