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Bulb Watering and Irrigation
Irrigating Bulbs
If you choose bulbs suited to your plant hardiness zone and climate, they will require remarkably little care [see Bulb Basics]. Of their few needs, however, regular in-season watering is most important.
Bulbs developed traits from growing in the wild that adapted them to the specific climate in which they grew.
Only Water When Bulbs Need It
Growing wild, they survived periods of drought by entering a near-dormant state. They will do the same in your garden. Only apply water during periods of their active growth. They should be left dry when growth ends and their foliage dies. Look each bulb species up in the chart that follows to learn when they need water.
The water bulbs need during when they are actively growing may come either from rain or from irrigation. Make sure that they receive regular watering as they break dormancy, grow, bloom, and store nutrients for their coming dormant cycle.
How Much Water?
The question often is, how often should we water and how much should we apply?
A good rule is to wait until the soil dries, then slowly apply 1 inch (25 mm) of water—envision an imaginary sheet of water that thick. Keep applying water to the soil above your bulb plantings until it is saturated 4–6 inches (10–15 cm) deep.
Spring-Blooming Bulbs
Generally, keep spring-blooming bulbs moist with regular waterings from the onset of warm weather until their foliage matures. Withhold water afterwards.
Keep them dry while dormant. Some Mediterranean climates naturally have long dry spells during summer. If summer rains are common for your region, lift and store spring bulbs in a warm, dry location after their foliage completely dries [see: Dividing Bulbs and Roots and Curing and Storing Bulbs].
Summer- and Autumn-Blooming Bulbs
Summer and autumn bulbs require watering throughout the entire gardening season, from spring planting until temperatures cool.
Reduce the amount of water applied to summer bulbs as autumn arrives, helping them to trigger their dormancy.
Continue to water autumn bloomers until the first frosts begin in cold-winter climates, or until the onset of winter in mild-winter areas. Move them indoors into cool, dry storage until spring [see: Dividing Bulbs and Roots and Curing and Storing Bulbs].
Evergreen and Tropical Bulbs
For evergreen and tropical bulbs, withhold water to slow their growth, starting 6 weeks after their blooms fade.
After several weeks, begin watering again. Another growth-and-bloom cycle will follow, provided sunlight hours remain long.
Some tropicals require other watering schedules; follow the recommendation for the species.
Water By When Bulbs Bloom
Water your bulbs using these recommendations for spring-, summer-, or autumn-blooming bulb varieties and for evergreen and tropical bulbs.
Water regularly for the period shown. During dormancy or when growth slows, withhold water.
Either lift, cure, clean, and store the bulbs, or remove old mulch and replace it to protect them as they overwinter in your landscape [see: Dividing Bulbs and Roots].
Always store lifted bulbs in conditions that will help avoid fungal disease or excess drying [see: Curing and Storing Bulbs].
Seasonal Water Need by Bloom Season
Florist’s cyclamen, glory-of-the-snow, Persian buttercup, snowdrop, snowflake, star-of-Bethlehem (spring), spring starflower, windflower: Keep moist autumn–spring.
Baboon flower (spring), cape cowslip, corn lily, freesia, squill: Keep moist autumn–summer.
Crocus, daffodil, hyacinth, tulip, wood hyacinth: Keep moist winter–spring.
Dog-tooth violet, fritillary, fumaria, grape hyacinth, striped squill, woodlily: Keep moist in spring.
Blood lily, bugle lily, camas, Dutchman’s-breeches, fan iris, Mariposa lily, lords-and-ladies, wood sorrel: Keep moist spring–summer.
Jack-in-the-pulpit, kangaroo-paw: Keep moist spring–autumn.
Calla lily, lily-of-the-valley, southern swamp lily, star grass, wake-robin, winter aconite: Keep moist year-round.
Hardy begonia, tuberous begonia (summer), caladium, canna, lily-of-the-Nile (deciduous), false lobster-claw, montebretia, pineapple lily, Scarborough lily, society garlic, tree gloxinia, tuberose: Keep moist spring–autumn.
Blazing star, daylily, elephant’s-ear, fire lily, gladiolus, bearded iris, gloriosa lily, torch lily, lily-of-the-Incas, bush morning-glory, bitter Indian nasturtium, orchid pansy, spider lily, tiger flower: Keep moist spring–summer.
Habranthus, summer hyacinth: Keep moist spring.
True lily: Keep moist spring–summer.
Dahlia: Keep moist summer–first frost.
Blackberry lily: Keep moist midsummer–early spring.
Aztec lily: Keep moist summer–early spring.
True amaryllis: Keep moist midsummer–early spring.
Freesia, snowflake (summer), star-of-Bethlehem (summer), wandflower: Keep moist autumn–spring.
Baboon flower (summer): Keep moist autumn–summer.
Ornamental onion: Keep moist winter–spring.
Ginger, true gloxinia, flag iris, zephyr lily (summer): Keep moist year-round.
Peacock orchid: Keep moist spring–summer.
Meadow saffron, naked lily, nerine, snowflake (autumn), winter daffodil: Keep moist autumn–spring.
Florist’s amaryllis, false lobster-claw, society garlic: Keep moist spring–autumn.
Elephant’s-ear, peacock orchid: Keep moist spring–summer.
Habranthus: Keep moist until late spring.
Florist’s gloxinia, lily-of-the-Nile (evergreen), Scarborough lily, star grass, zephyr lily (semi-evergreen): Keep moist during active growth; reduce watering for 1–2 months after bloom has been completed to rest the plant.
Step-by-Step Instructions
Regular waterings during periods of active growth—usually performed weekly—are essential to making your bulbs grow and bloom.
Don’t skip waterings. Bulbs are more sensitive to moisture than other garden plants.
When the soil around bulbs becomes dry, they slow their growth and prepare for dormancy; missing several waterings will stop their bloom for that entire season.
Note the amount of water received from rains during the time that the bulbs are sprouting, growing new foliage, and sending up buds, and apply more if it is needed.
For most species, the soil should remain evenly damp or moist. If a dry spell lasts more than a week, gather your hose and a diffusing nozzle in the morning after the air has warmed, and follow these steps to water your bulbs:
How to Irrigate Bulbs
Overhead watering, whether by hand or with automatic sprinklers, is best for most bulbs. To gauge the amount applied the first time you water, place clear plastic cups in several places throughout the planting before you water.
Note the start time. Apply water evenly to the bed. If the water begins to run off, allow a few minutes to pass, then reapply water until the soil is saturated.
When your test cups have filled with an inch of water, note the time it took to fill them. The bed should be watered adequately. In the future, apply water for that length of time each time you water.
Water soaks into soils differently depending on their texture. Wait 30 minutes, then carefully dig down 6 in. (15 cm) with a hand trowel. Avoiding any bulb stems. Confirm that the water has penetrated at least 4 in. (10 cm) into the soil.