Squirrels naturally dig to bury acorns, seeds and other bits of food for later, and they are readily attracted to a freshly dug garden or flower box with nice, soft dirt. Squirrels also eat many flower bulbs, and a few hungry squirrels can quickly undo hours of hard work in your flower boxes. Stop squirrels from digging in your flower boxes and garden with barriers and squirrel-repellent spray or powder.
Add a barrier when planting your flower boxes. Cut a piece of hardware cloth, heavy metal screening or chicken wire fencing to fit inside your flower box, and cover it with soil. The flowers will be able to sprout around the wire, but squirrels won't be able to dig through it to get to the bulbs or seeds below. Depending on the size of the flower you are growing, openings in the screen should be about a half-inch to one inch in size. Place stones or gravel over the top of the soil to help hold the wire in place.
Apply a squirrel-repellent spray to your flower boxes. These are available at any garden center, and they usually smell or taste bad to deter squirrels and other pest animals. Apply the spray early in the spring, before the squirrels can get in the habit of digging up your flower boxes. Most sprays must be reapplied several times throughout the summer and after heavy rains.
Sprinkle a light dusting of blood meal over the soil of your flower boxes. Squirrels find the smell to be unpleasant and will avoid the area. A few applications per season is sufficient. Blood meal also adds nitrogen to the soil, which will produce more flowers and bigger blooms.
Sprinkle powdered cayenne pepper over your flowers to keep squirrels and other animals from eating them. You don't need a lot, just enough to lightly speckle the flowers and surrounding soil. You can also make a spray from hot pepper sauce and water, then apply the spray to your flower boxes. Use about one teaspoon of hot sauce per quart of water. Persistent squirrels might require a stronger pepper solution. Reapply the spray after rains, or as needed.