Both walnuts and almonds were commercial crops in Napa County until grapes took over. In fact the Hartley walnut, now the most widely planted variety in the state, was developed in Napa County.
Pistachios, pecans and chestnuts are also appropriate trees for Napa County, although they have never been grown here commercially. All of them make nice shade trees, and if you can beat the squirrels to the crop, you can harvest some nuts as well. These nuts mature at slightly different times but have similar harvesting and storing requirements. Chestnuts require some different treatment for harvesting and hulling and don't require drying.
Walnuts ripen from early September through early November. They are considered ripe when the hull (also called the husk) darkens and becomes loose.
Pecans mature from late September through November and are considered ripe when the outer husk splits open and the shell within is completely brown.
Almonds ripen from early August through late September. They are ready to harvest when the hulls split and expose the shell with the nut inside.
Pistachios ripen from late August to early September and are mature when the hull changes from green to red and you can easily remove the nut from the shell.
Chestnuts are ripe when they fall to the ground. The nuts on a chestnut tree don't ripen evenly, so do not knock them off to harvest them.
For other nuts, you can use a pole or rubber mallet to knock the crop from the trees. Wear head and eye protection to prevent injury, and spread tarps under the trees to keep the nuts clean and prevent contamination from soil fungus. Collect fallen nuts promptly to
Remove the hulls soon after harvest to prevent spoilage and nut darkening. Use metal hardware cloth with a half-inch mesh, available at hardware stores. Rubbing the hulls against the mesh will help break them off. To make the job even easier, mount the mesh screen on a wood frame. Wear rubber gloves to protect your hands when hulling walnuts. The hulls contain chemical compounds called phenols that can stain hands and irritate skin.prevent insect and animal damage.
For chestnuts, which have a spiny husk, you will need heavy leather gloves.
All nuts except for chestnuts need to be dried if you intend to store them. If you fail to dry them sufficiently, they may develop mold and turn rancid quickly.
To dry nuts, spread them in a single layer on trays or screens in a shady or partially shady location with good air circulation. Cover them with netting or an additional screen to foil birds. Stir the nuts daily and cover them completely if rain threatens.
Crack open a few nuts every few days to check for dryness. The kernels inside should be crisp, not rubbery. In late summer and fall, drying may take only three to four days. Pecans should be dried more slowly to prevent the hull from cracking. A drying temperature between 75 degrees and 85 degrees Fahrenheit is best.
Properly dried nuts, shelled or unshelled, can be stored for up to a year at 32 to 45 degrees F. A typical home refrigerator is between 38 to 45 degrees. Most home freezers are around 32 degrees. Chestnuts still in their shells will keep only about a month in the refrigerator.
For more detailed information, consult the following publication: “Harvesting and Storing Your Home Orchard's Nut Crop: Almonds, Walnuts, Pecans, Pistachios and Chestnuts” (UC ANR Publication No. 8005). You can download this document at no charge from anrcatalog.ucdavis.edu/ or get it from the Napa County Master Gardeners office.
Napa County Master Gardeners (cenapa.ucdavis.edu) answer gardening questions Monday, Wednesday and Friday, 9 a.m. to noon, at the UC Cooperative Extension office, 1710 Soscol Ave., Suite 4, Napa, 253-4221, or toll-free at 877-279-3065.