The key to having effective whimsy in a garden, in my opinion, is balance--not too little, but more important, not too much.  A whimsical piece in the yard should be slightly hidden
and a surprise when discovered.  Whimsy should make one at least smile, if not chuckle.  It should fit well with the feeling  of the garden as a whole, and not feel, when discovered, out of place.

Articles of whimsy are usually obtained in unexpected ways.  One does not set out to find a cute gnome, but comes across one at a garage sale or "steals" one from a friends garden, later to be mysteriously returned of course.   Looking through a catalog, one might, by chance, see the perfect bunny family for the fern bed and impulsively send away for it.  I recently came across a small sign in a catalog I feel I absolutely must have.  It said, "Ha!  I don't remember planting this here!"

Garden and home decorating magazines are full of ideas which one can adapt to their own needs.  Some of my favorites are pots turned on their sides with flowers planted in such a way to appear to be cascading out of the fallen containers, birdhouses made out of unexpected materials or objects such as old mailboxes, and recently I saw a magazine picture of a non-functioning faucet stuck among some greenery with a sparkly crystal appearing to be "dripping" out of the spout.  For those of you lucky enough to have a pond or a stream, placing some floating glass balls of various sizes securely in appropriate places on and near the water can hint that there is a fairy hiding in the nearby foliage, blowing bubbles.

Whimsy is such a fun way to personalize your garden space.  It can easily reflect your love of butterflies, frogs, cats, or antique cars as well as your hate for snails.  For a long time, we had a ukulele playing toad guarding our storage shed door, reflecting my husband's interest in uke playing.  It can be as simple as a cute, funny welcoming mat on your porch.  It can be as complicated as a musical water fountain that plays "Tip Toe Through the Tulips."

If you want your garden to have a bit more of a serious feel, a simple, beautiful resin butterfly attached to your fence or a small cat statue among some pots can be effective and bring something unique and personal to your garden.

Is whimsy essential to a garden?  No.  But the placement of that one great object in just the right place can enliven and enhance your environment, giving more pleasure to you and all those who are lucky enough to be invited in.