Water the bulbs well following planting. This will help settle the soil in the planting bed plus provide needed moisture for the bulbs to start rooting. Fall planted bulbs must root before cold weather. Avoid over-watering at planting time since this can result in bulb rot.
Average spring conditions should provide enough moisture for your bulbs. However, if the weather is unusually hot and dry, a weekly deep soaking will produce larger, longer-lasting blooms. For both spring and summer bulbs, start watering when the flower buds first appear on the plant if the soil is dry. Remember that the bulbs may have been planted 6 to 8 inches deep and the water needs to soak to that depth. Through the bud, bloom and early foliage stage, add about one inch of water per week if this amount has not been supplied from rainfall. Water with a soaker hose to keep water off the bloom. Bulbs like alliums, or the shallow planted bulbs, will rot quickly if over-watered in the heat of summer.