To support the flowers, the bulbs need to establish a root system. Planting in the fall allows the bulbs to develop the strong roots needed for quick spring growth. Plant bulbs when the soil begins to cool after the heat of summer. Roots will grow until the ground freezes so the earlier they're planted, the more time they have to develop that system. Generally, this means at least six weeks before the first hard freeze. You want the soil to be warm enough to sustain root growth, but the conditions shouldn't be so warm that foliage growth happens; that's why we don't call them "summer bulbs".
If you delay and have bulbs in storage, having missed the perfect time to plant, it's best to get them in the ground even late in fall or into winter. With time bulbs will dry out and when they do they lose the energy needed for plant growth. This year's bulbs need to be planted this year. They may not develop a healthy root system before spring but at least they have a chance for survival.
Very warm regions, like Zones 8 and 9, can grow spring flowers from bulbs, but some of this timing needs to be modified. Most of the spring flowering bulbs, particularly hyacinth, crocus, and tulips, need cold saturation so the bulbs should be stored in the refrigerator for six to eight weeks before planting. The bulbs should be planted in early winter and treated as annuals; bulbs need to be re-planted each year. Either purchase new bulbs or dig up old bulbs and put in cold storage, but they need the cold temperatures to bloom again. Amaryllis, lilies, and daffodils don't need the cold treatment.
The bulbs you choose should be large, firm, and show no signs of mold, fungus, or decay. Buying from reputable online sources or a local nursery or garden center where you can actually examine the bulb ahead of time is the best idea. Typically you get what you pay for. If you buy bargain bulbs from a discount online or mail nursery, you may get scrawny, dried out, damaged inventory; I know because it's happened to me. Inexpensive bulbs in garden center bins can be fine, but examine them before you buy.
Look to bulb producers that develop bulbs in a region similar to the one for your garden. Do a little research and select bulbs that are appropriate for your climate and plant growing zone. Don't just focus on how pretty the flowers will be. The plant must survive your winter to bloom in spring.
When choosing a location for planting fall bulbs look for a sunny, well-drained area; bulbs don't like wet feet. Be sure to look into the future. The sun needs to shine on the plants in the spring. Deciduous trees won't have leaves in the spring and the sun's position in the sky is different than fall, so areas that might be shaded in fall may be in full sun in spring, and vice versa.
Consider how you want to establish your bulb bed. Remember that fall bulbs bloom in spring and most of the flowers don't last longer than a few weeks. For the entire summer and into the next fall, the area will be devoid of color as the foliage gradually begins to brown. Many gardeners prefer to intersperse other flowers in the same beds during that time. Whether annuals or perennials, having other plants in a bulb bed helps sustain continued color throughout the growing season.
If you're developing a new bed it's best to prepare the entire plot by amending the soil and adding a slow-release fertilizer to a large area all at once. The bulbs can be planted in the fall, grow and bloom in spring, and lay the framework for additional plants. At the appropriate time, other flowering plants can be placed among the bulbs.
If you're adding bulbs to an established bed with other perennial plants already in place, you'll need to plant one hole at a time. This is more time consuming, but follows the same basic idea of interspersing plants that flower at different times of the year.
With bulbs in hand, and the weather cooling, begin fall bulb planting. Generally speaking, use a "rule of three". Plant bulbs about three times as deep as the height of the bulb and space them apart at least three times the width of the bulb. Some large daffodil bulbs may be almost three inches tall and thick (8 centimeters). Yes, they should be planted about eight inches deep (20 centimeters) with eight to nine-inch spacing. Keep this in mind when you buy mass-produced, bargain bulbs. The directions for planting tulips and daffodils were exactly the same for bulbs I bought at a garden center though the bulbs were markedly different in size.
You can use special bulb tools or the ones you have already. I have a bulb planter, a special cylindrical tool than is designed to twist in the soil and pull out a plug, producing a perfectly-shaped hole. If you want to buy one of these, look for one that has inch or centimeter markings so you know how deep you're digging. I also have a trowel with depth markings. They both were a little more expensive than generic tools, but they come in very useful when I want to measure the hole depth for different bulbs.
In a bed with other plants already in place, I lay out my bulbs ahead of time in the desired pattern on the surface. In a brand new bed you can dig a trench or large hole of the appropriate depth to place the bulbs in. Some gardeners like long, orderly rows of flowers. Others like clumps of flowers. Others like a totally random arrangement where the bulbs are tossed on the ground and planted where they land. I use all three methods and vary them depending on which bed I'm planting. Clumping or planting a lot of bulbs in one area is better than a few, single ones because the concentration of color can provide quite a visual impact.
Using the bulb tool or a trowel, dig the hole, or prepare a trench. Place the bulb with the pointed end up. The flat end is wider and fatter and should be at the bottom of the hole. With smaller bulbs it may be difficult to discern which is the base and which is the top; just put it in the hole and the plant will adjust when it grows.
If you weren't able to amend the soil in the entire planting area, do it one hole at a time. Mix some compost and fertilizer with the soil at the base of the hole. While the bulb has all of the energy needed to produce a plant and flowers in the first year, slow-release fertilizer high in phosphorus (the second number on the box) helps with plant development in poor soil like mine. I use a triple phosphate fertilizer. If the soil has been amended and is rich with organic matter, fertilizer isn't necessary. Avoid just adding the fertilizer directly to the hole because it can burn the developing roots.
After placing the bulb, cover it with amended soil and tamp down gently. You don't want to compact the soil, just ensure it is completely covering the bulb. Especially after amending it you'll have more soil than will fit in the hole with the bulb in it. That's okay. You can mound it slightly because it will settle in time.
Be as creative as you want when it comes to planting fall bulbs. Generally, low plants are planted in front of high ones, but consider blending and mixing different bulbs in the same bed. When flowers bloom at different times they'll provide an ever-changing spring portrait. Consider planting different bulbs in the same hole with smaller ones on top of large ones. When they grow and bloom the flowers will be mingled with each other for a distinctive look. Bulbs do well in pots too.
As easy as they are to plant and as beautiful as the flowers are, it's hard to come up with an excuse for not planting fall bulbs.