Arizona consists of United States Department of Agriculture plant hardiness zones 5 to 10--a wide range of climates ranging from average winter low temperatures from minus 20 degrees F to 30 degrees F. Most bulbs planted in Arizona can be cared for in a similar manner; however, some different care will be needed for bulbs during the fall and winter months.
Water your bulbs weekly during the growing season (spring until fall for most areas with frost, all year in the warmest zones) if rain has been scarce, which is usually the case for Arizona zones 9 and 10. About 2 inches of water will suffice, however when the bulbs are in bloom, water twice a week.
Deadhead--or pinch off--flowers, using your fingers, after they are done blooming. This will prevent the plants from using valuable energy into forming seeds and will instead bloom more and for a longer period of time.
Stake taller bulbous flowers to give them support. Examples of bulbous flowers that grow in Arizona and may need support are some taller varieties of cannas, dahlias, gladioli and lilies. To stake flowers of any variety, insert a wooden, metal or natural stake (such as a branch) about 2 to 3 inches into the ground near the base of the plant. As the flower grows, loosely tie the flower with twine to the stake near where the flower is bending. You may have to add more loose ties as the plants grow.
Fertilize your bulbs. Many gardeners suggest different times and rates of fertilizers. However, according to the University of Arizona, fertilize bulbs once a year after they begin blooming with a fertilizer labeled 5-10-10. Use 1 lb. for every 50 square feet. Apply the fertilizer according to manufacturer directions, and to prevent burning, don’t let it touch the leaves or roots.
Cut off the foliage only after the leaves have yellowed and withered in the fall, usually after the first frost. Use pruning shears to cut the foliage off near the ground. Cut straight across. If the leaves do not yellow in your zone (usually zone 10), leave them alone.
Mulch over the bulbs hardy in your zone during the winter months, especially in zones 5 to 7. Use about 2 to 4 inches of organic mulch, such as bark or straw. This will help prevent the bulbs from freezing and thawing during winter temperature fluctuations. Remove the mulch in the spring after the last frost.
Dig up tender bulbs during the winter after you cut off the foliage. Use a spade, shovel or garden fork to dig a circle around each plant. Then push down on the handle in several spots to gently lift the bulbs out of the soil. Many summer-blooming bulbs (cannas, dahlias) will be tender in the cooler zones in Arizona. Tender bulbs are planted at varying depths (e.g., cannas about 6 inches deep); however after you dig up the first bulb, you will have a good idea how deep the others of the same kind will be.
Store tender bulbs during the winter. Bulbs are stored in different ways. The label that came with your bulbs may tell you how they are stored, or you can check with your local nursery or university. Some tender bulbs, such as dahlias, are stored buried in sphagnum peat or vermiculite and then placed in a cool, dry area that is around 50 degrees F until the spring, when they can be planted again after the last frost.
Replant the bulbs to the same depth as they were planted before. True bulbs and corms are planted with the tips facing up. Other bulb-like structures, like rhizomes, are planted on their sides; and tubers with the eyes facing up. Backfill the soil and lightly pack it down to fill in any gaps of air. Water the area weekly with about an inch or two of water.