Sunny, cool weather is perfect for being outside planting bulbs. What's the perfect tool for this job?
A bulb planter -- looking like a tin can without top or bottom, with a wooden handle attached to its rim -- is made for this job, but even a trowel works well in a flower bed. Stab the trowel into the soil full depth with the concave side facing you, then pull it toward you. Snuggle a bulb into the bottom of the hole, then push the dirt back in place over it.
A trowel is definitely more useful than a bulb planter for planting bulbs t the base of a tree or in rocky soil. With the trowel, you can open up small planting slits among the roots or rocks.
Planting bulbs for naturalizing in a grassy field is a little trickier than planting in a cultivated bed. In this case, use a bulb planter that has a long handle and a place on which to put your foot to force the tool into the soil. This sturdy tool can remove a plug of grass and soil. Drop a bulb in the hole, again ensuring good contact between the base of the bulb and the soil. Then replace the plug, firming it in place. The work is slow, but a naturalized planting needs no further care for years, perhaps decades.
Rather than invest in one tool just for planting bulbs, you could this naturalized planting using a shovel, preferably one with a long, narrow blade. In this case, dig up a small flap of vegetation and fold it back wherever you want to plant. Then dig a hole just large enough for a bulb, cover it, and replace the flap, firming it in place with your foot.
To plant a cluster of bulbs, use your shovel to cut out, lift, and fold back a large flap of grass. Then, in the exposed dirt, dig holes and plant. When you're finished, replace the flap and stomp on it to firm it in place.
The replaced flap of grass insulates the soil and delays freezing so that the bulbs can grow roots now. When planting in bare soil, cover the ground with some mulch to delay freezing. Depending on how thick the mulch is, it may have to be pulled back in early spring to let the growing leaves through to the light.