Squirrels and chipmunks are a common and mostly benign sight in the landscape. Most gardeners enjoy their antics without concern.
Squirrels and chipmunks eat seeds, berries, bark, and flowers. A typical landscape offers enough food sources to keep them from becoming pests in the garden. Conflicts with these rodents arise when they dig up bulbs, eat the blossoms from tulips, uproot container plants, or raid your crop of berries or nuts. When water is scarce, thirsty squirrels will also “drink” from developing tomatoes and melons in your garden.
When possible, use netting to exclude squirrels from nuts and berries. Top bulb plantings with a piece of poultry netting on the surface of the soil to deter digging. Repellent sprays for deer and rabbits may also be useful against squirrels. Drench the soil of container plants with castor oil repellent (sold for mole control) to discourage squirrels; regular applications are necessary for best results.
This article is courtesy of The Organic Gardener's Handbook of Natural Pest and Disease Control.