When you shop, look for plump, firm bulbs that feel heavy for their size. Avoid soft or squashy bulbs; they may have some sort of rot. Also steer clear of lightweight or shriveled bulbs, since these may have lost too much moisture to recover well.
Large bulbs are likely to give the most impressive performance: the biggest tulip (Tulipa) and daffodil (Narcissus) bulbs, for example, produce larger flowers on taller, thicker stems. But if you're willing to give bulbs a year or two to build themselves up in your garden, you'll get fine results with smaller sizes of most kinds of bulbs - and their lower cost makes them a good buy.
Like most plants, bulbs need good drainage. If your soil drains very poorly, it's best to plant on a slope or in raised beds.
You can prepare an entire bed for bulbs alone, or intersperse bulbs among existing plants. To plant a bed, remove weeds and other vegetation; then spread 1 to 3 inches of an organic amendment over the soil and sprinkle on a complete fertilizer, following the label directions for amounts. Dig or till in these additions, rake the soil smooth, and you're ready to plant.
In most soils, bulbs should be planted about three times as deep as the bulb is wide. In hot climates or sandy soils, plant slightly deeper; in heavy soils, plant slightly shallower. Most bulbs can be set quite close together to provide a mass of bloom, but keep in mind that closely spaced bulbs will need dividing sooner than those given more room to grow. For spacing, check with the nursery when you buy.
To plant bulbs among other plants, use a trowel or bulb planter to dig a hole for each bulb, making the hole a couple of inches deeper than the recommended planting depth. Put up to a tablespoon of complete fertilizer in the hole and cover it with 2 inches of compost or soil; then set in the bulb and fill in with soil.
After planting, water thoroughly to establish good contact between bulb and soil and to provide moisture to initiate root growth.
Bulbs need water during their season of active growth. For most kinds, this period begins soon after planting and continues until the foliage dies back (either after flowering has finished or in autumn). If you must supplement rainfall, water deeply enough to penetrate the root zone; the roots grow beneath the bulb. A layer of mulch helps retain moisture. (Bearded iris are an exception; they will rot if mulched.)
In addition to applying fertilizer at planting time, give your bulbs a feeding of high-nitrogen fertilizer at the start of the growing season, to enhance the quality of the current season's flowers.
After bloom ends, much of a bulb's stored nutrient supply is gone. If it is to perform well the next year, those nutrients must be replenished. To make sure the bulb has enough food to store, you can do two things.
First, always leave the foliage on the plant - even if it begins to look unsightly - until it has yellowed and can be pulled off easily. As long as the leaves are green and growing, they continue to manufacture food for the plant and for next year's flowers.
Second, apply a complete fertilizer as the flowers fade, using a 10-10-10 formula or a "bulb food" high in phosphorus and potassium. Because phosphorus and potassium must reach the root zone to be fully effective, you'll need to get the fertilizer as close to the roots as you can. In an established planting, scratch the fertilizer lightly into the soil to help it move deeper; then water thoroughly. Or, if there's enough space between bulbs, dig narrow trenches (up to 8 inches deep) close to the plants, taking care not to damage the roots. Scatter fertilizer in the trenches, cover with soil, and water.