One of the most destructive pests at our farm, and in gardens and landscapes in the California Bay Area, is the California Pocket Gopher. Some detailed information about this pest and how to control it is given at the University of California Integrated Pest Management website: http://ipm.ucanr.edu/PMG/PESTNOTES/pn7433.html
The ways we use to reduce gopher damage include:
Protecting the adjacent urban forest, which provides habitat for Great Horned Screech Owls and Red Tail Hawks. We have an adjacent forest with eucalyptus, walnut, and oak trees that provides habitat for owls and hawks. If you don’t have tall trees with large screech owls near your garden, then another owl that can be helpful in controlling gophers is the Barn Owl. You can attract barn owls by installing a barn owl box. Barn owl boxes can be purchased at www.barnowlbox.com.
Trapping the gophers with traps. We’ve had the most success with the Cinch medium-sized gopher trap. Cinch Gopher Traps It can sometimes help to bait the Cinch Traps with peanut butter. Another trap that is highly reviewed by other organic farmers (we’ve had less experience using this one) is the Gopher Hawk. https://gopherhawk.com/
Planting valuable young trees into gopher wire baskets. Figs are especially attractive to gophers and need to be protected for the first few years. RootGuard Gopher Wire Baskets
An option that we don’t currently use, but I’ve used successfully at my home garden is to asphyxiate the gophers using sulfur. I learned of this gopher treatment method from a book “The Grape Grower – A Guide to Organic Viticulture” by Lon Rombough.
On page 136 of this book it is written:
Trapping a gopher is possible, but it may be hard with a wary old-timer, and it is a slow, time-consuming process. The most effective method I have found is gassing, not with gopher bombs – which almost never produce enough gas to be effective – but with a propane weed torch.
To use a propane weed torch in this way, find a fresh mound and open the tunnel nearest it. Put in a handful of sulfur flakes (sold as “sugar sulfur” in farm and agricultural supply houses) and play the flame of the torch on the sulfur, igniting it and forcing the fumes down into the tunnels. After a few minutes you should see yellow fumes puff out of the ground as much as 20 feet away as the sulfur dioxide reaches the other end of the tunnel. Continue for another five minutes or so, then close the tunnel. The sulfur and the fumes oxidized and are harmless to the soil, and you can be sure any gopher in that tunnel is a deceased gopher.
Unfortunately, the USDA removed this means of gopher control using sulfur fumes from the organic standards in about 2014, so we haven’t been able to use it at our farm. I see no reason, however why homeowners with backyard gardens couldn’t use it – they just can’t make the claim that they are ‘organic-certified’. If you choose to try this approach, be careful to avoid breathing the fumes and don’t do it on a dry windy day when fire hazards are extreme. Keep the flames well- away from dry weeds and brush. The weed flamer that I used was the Red Dragon Flame Weeder Torch. Red Dragon Flame Weeder You can purchase soil sulfur at Peaceful Valley Farm Supply, or perhaps at one of our local nurseries or home improvement stores. Soil Sulfur
Hope this information gives you some new approaches that will be of help to you.