Remove the clues.
Squirrels and other animals operate on scent cues, so clean up all debris after planting. This includes any paper packages in which the bulbs were wrapped, plus tools, pots, leftover soil, etc.
Trick their noses.
The smell of rotten eggs may be hard on you if you keep your windows open, but some gardeners swear by these egg mixtures; the rotten-egg smell drives most creatures away. You can use commercially available mixtures or just rotten eggs from your own kitchen. Predator scents such as lion's dung or urine are also available for purchase. Contact your local garden supply store.
Mulch correctly.
Mulching helps your soil retain moisture and maintain proper temperature for your bulbs. But avoid mulching until after the weather turns cold. If you mulch too early, you'll give small creatures a cozy, earth-warmed place to burrow into for the winter. Then they'll just happily nibble their way through your bulbs.
Take up fencing.
Deer can jump very high and very wide, but not at the same time. So, the best deterrent for them is a double fence set about three feet apart—one very high (about a 7 ½-foot fence) and the other one wide. With such a structure, deer apparently see two fences and balk because they don't want to get caught inside. Avoid electrified fences for humane reasons.
Chicken wire.
It may be old-fashioned but it still works: just place a sheet of chicken wire right on top of the planted soil. And don't worry—bulbs seem to know intuitively how to burst through the empty spaces. Or throw an old window screen on top and remove it once the ground is frozen or settled.
Plant a deterrent.
Surround your precious bulbs with plants your predators don't like. For example, deer despise plants with thorns. They also won't eat anemones, astilbes, junipers, foxgloves, daffodils, ferns, grasses and more. Last year I surrounded my fall bulbs with a ring of daffodils and ferns as a deterrent. Crown Imperial (or
Fritillaria imperialis) has a skunky scent that repels many animals. Squirrels won't eat daffodils or other narcissi bulbs.
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Host an alternative feast.
If you can't beat 'em, feed 'em! First, make sure you haven't left out any teasers (like bulb papers, etc.). Then leave some peanuts or corn in tree feeders for squirrels during their fall nut-gathering season. This is the technique favored by the National Park Service in the gardens at the White House!