If you plant a walnut tree now you can look forward to watching your grandchildren climbing 100 foot trees to pick some walnuts - that's assuming they won't be fiddling with some new fangled video games.
Starting From Seed
Walnut trees can be started from seed, either in a container for transplant when they become saplings, or they can be direct seeded where you intend the tree to be grown. They have very deep central tap roots, which makes container growing as well as transplant difficult - but it can be done.
Store bought walnuts come from Commercially grown walnut trees, which are a tree stock grafted to a root-stock of a differing variety. When walnuts germinate from seeds, they produce trees suitable for root-stock but not necessarily for producing walnuts . Nuts produced vary widely from the parent tree. If you still want to try walnuts from seed and have a decade to see what kind of nuts your tree produces - good luck.
To successfully germinate and grow walnuts from seed requires cold stratification - a period of cold temperature.
Soak the walnuts overnight. Place them in a plastic bag. Keep them outdoors over winter in moist sand or peat moss will achieve this. Refrigerating them for 2- 3 months will also do the trick. Once planted under 2 -3 inches of soil - they should sprout in about 5 months.
Starting From Grafted Saplings
The best way to start walnut trees is from grafted saplings. If you are only planting one tree be certain it is a self fertile variety such as Black Walnut.
Two or more trees is always best, even with self fertile varieties as it ensures a better quality and higher quantity crop. Place your tree away from where any other plants will be cultivated - walnut trees are bad neighbors to the rest of the plant kingdom.
Their leaves and roots emit a toxic compound known as juglone, which will kill any other plants that come into contact with it - this includes lawns and other trees. Due to the juglone, you'll also want to dispose of your walnut leaves somewhere besides the compost heap.
See - Alleopathic Plants
Planting Walnut Trees
Dig a hole almost twice as deep as the root ball, then back-fill it slightly with loose uncompacted soil - a little compost worked in wouldn't hurt none either - just a little. The soil beneath and above the root ball should be uncompacted and loose to allow for root penetration, water penetration and oxygenation. Keep the sapling well watered the first few months when the roots are getting established in their permanent home.
Care and maintenance of walnut trees is a snap. Walnut trees don't need any pruning and should be left to grow naturally. They don't have any issues with competition from other plants - they kill other plants via their juglone emissions.
Mature walnut trees have a vigorously long and deep root system, which generally excludes them from any surface moisture problems. Only after prolonged periods of heat and drought will mature trees need watering. Water stressed trees will produce dry and burnt nuts.
Harvest and Storage
Walnuts grow within a husk which is initially green, but blackens inwardly as it ripens. Ripe black husks can be a nuisance to handle, they are messy and the black resin from the husk stains skin and clothing.
The husks are actually an inedible fruit. You can pick them when they approach maturity - but its best to allow them to fall off the tree of their own accord.The nuts should not be left inside the husks for too long as the husk oils will penetrate the nut shell, and ruin the nut meats. Remove the walnuts as soon as they drop.
Over ripe nut husks frequently host worms, these worm rarely penetrate the nut shell - only the husk.
The husks are very tough and can be difficult to remove. Soak them for a day to soften them. Wearing protective gloves is advisable when separating the husks from the nut's.
Once you've removed the husk and washed of any husk residue store your walnuts somewhere warm and dry for a few weeks. You can test for sufficient drying by cracking one open a nut and checking the septum - a woody filament that separates the two halves of the nut meat It should be hard and crisp. If its still soft, the nuts aren't sufficiently dried.