Squirrels may nibble on some flowers and trees, dig holes in lawns and even chew on wooden decks and furniture. Before you blame the squirrels though, make sure the damage isn't caused by another animal.
Squirrels are only active during the day, so you should be able to catch them in the act. Squirrels generally don't do significant damage to plants, but if a squirrel is indeed the culprit, keep them away from the plant with fencing or a wire mesh cage.
Small fruit and nut trees can be protected by netting the entire tree for the short period when squirrel (or other animal) damage is most likely. Fruit trees may be protected by wrapping a two-foot band of sheet metal around the trunk about six feet off the ground, as long as the squirrels cannot jump on them from adjoining trees. Do not to leave the bands on any longer than necessary, since insect damage might occur and the trunks of sensitive trees may get sun scald (the freezing of bark following high temperatures in the winter season, resulting in permanent visible damage) if bands are removed after a long time. Branches growing below six feet also may have to be trimmed.
Squirrels will dig up and eat tulip and crocus bulbs, but they don't like daffodils, so consider investing your bulb-planting energies in daffodils. For other bulbs, soak them in a repellent with Thiram as the active ingredient (and labeled for use as a squirrel repellent) before planting. Lay chicken wire over the planting bed or use wire bulb cages.
The tiny holes, about the size of a quarter, that seem to pop up all over the lawn in the fall are likely to be a sure sign of squirrel activity. Squirrels bury or cache their winter food supply and rely later on an incredible sense of smell to be able to relocate their buried treasure. Any "damage" they create in these activities is likely to be so slight that tolerance and time are all you need. The lawn will heal itself by spring. Just consider it free aeration for your lawn!
Wood decks and furniture
If squirrels are gnawing on deck railings or wooden lawn furniture, try capsaicin-based repellents (see below) or lightly rubbing the exposed surfaces with a bar of soap. Use caution with capsaicin; it can be transferred to your hands and will cause intense irritation if you rub it into your eyes.
A note on squirrel repellents
There are several repellents on the market that may deter squirrels. In addition to repellents with Thiram as the active ingredient, there are ones with capsaicin or oil of mustard as active ingredients, which you can spray on plants when they first emerge in the spring. You can also use these repellents on patches over squirrel entry holes in buildings to discourage gnawing in attempts to re-enter.
Capsaicin products are also used to coat birdseed to repel squirrels. Birds aren’t irritated by capsaicin-based products, but mammals are. However, we don’t recommend using capsaicin-coated birdseed because there are less harmful, more effective ways to keep squirrels out of bird feeders.
The sticky gels that are marketed to deter squirrels from climbing on branches or other surfaces are dangerous to other wildlife, particularly birds, and inappropriate for wildlife control, not to mention that they can cause damage to surfaces on which they are placed. We don’t advise you to use them.