Quick Answers
Iris bulbs can be kept out of the ground for up to 1 year if stored properly. The ideal storage conditions are cool (35-45°F), dry, and dark. Storing the bulbs for over a year may result in decreased flowering or failure to sprout when replanted.
Iris bulbs are a popular choice for gardens due to their beautiful and diverse flowers. Irises come in many colors like blue, purple, yellow, pink, red, white, and bi-colors. The flowering period for most irises is mid to late spring. After flowering, the foliage dies back and the bulbs become dormant over the summer. Iris bulbs are typically planted in the fall, but it’s common for people to dig up and store bulbs they want to reuse the following year. This brings up the question – how long can you keep iris bulbs out of the ground before replanting them?
How Irises Grow
Iris bulbs are actually rhizomes, which are horizontal underground plant stems that store food and nutrients. The rhizomes grow new shoots and roots each year. In the spring, the shoots grow up through the soil and produce leaves, stems, and flowers. After flowering, food produced by the leaves is sent back to the rhizome to fuel next year’s growth. The foliage dies back and the rhizome goes dormant over the hot summer months.
When iris rhizomes are dug up, they have no way to photosynthesize until replanted. The stored energy in the rhizome must be conserved as much as possible to ensure the iris will grow and bloom the following year. Proper storage is key to maintaining the health of the dormant rhizome.
Ideal Storage Conditions
To keep iris rhizomes viable for replanting, they need to be stored in conditions that mimic their natural overwintering process in the garden soil. Here are the ideal storage conditions:
- Cool Temperature – Rhizomes store best between 35-45°F. This cold but above freezing temperature simulates winter dormancy. Storing rhizomes somewhere with large temperature fluctuations or excess heat can lead to mold, rotting, and depletion of resources.
- Dry – Moisture encourages mold and rotting, so the rhizomes should be kept dry while in storage. Sprinkle bulbs with a fungicide prior to storage to prevent issues.
- Dark – Light stimulates growth, so store bulbs in complete darkness. A frost-free garage, shed, or basement is ideal.
- Ventilation – Some airflow around the rhizomes prevents excess moisture buildup.
Peat moss, vermiculite, perlite, or sand can be used to pack around bulbs to maintain an evenly cool and moisture-controlled environment. Punch holes in plastic bags or containers to allow for some air circulation.
How Long Can Iris Bulbs Be Stored?
If given proper dry, cold, and dark storage conditions, iris rhizomes can typically be kept out of the ground for up to 1 year.
Iris experts generally recommend replanting iris rhizomes within 2-3 months after digging them up. This ensures optimal flowering and growth the following year. However, you can still expect decent results if forced to store the rhizomes for 6-12 months due to weather or other restrictions. Beyond one year, the bulbs start to seriously deteriorate.
Here is an overview of how duration of storage affects replanting success:
| Storage Duration | Expected Growth After Replanting |
|---|---|
| Up to 3 months | Excellent growth and flowering expected |
| 3-6 months | Good growth and flowering |
| 6-12 months | Moderate growth and flowering |
| Over 12 months | High failure rate; limited growth and flowering |
Up to 3 Months
Replanting iris rhizomes within 0-3 months after digging them up generally provides the best results. The rhizomes are still fresh and have relatively undiminished energy reserves. You can expect excellent growth and flowering the following year with proper care after replanting.
3-6 Months
Storing iris rhizomes for 3-6 months is still safe if done properly. Some loss of vigor may occur, but the rhizomes usually still have enough stored resources to generate good growth and flowering the next season.
6-12 Months
Between 6-12 months, stored iris rhizomes become depleted. However, replanting within a year of digging should still yield moderate growth and flowering. Blooms may be reduced and foliage may be weaker. But with proper care after replanting, most rhizomes should still survive.
Over 12 Months
Storing iris rhizomes for over a year often leads to failure and death of the bulb. Without soil nutrients and the ability to photosynthesize, the rhizome’s resources become dangerously low. While some very hardy iris varieties can sometimes survive longer storage, growth and flowering is severely decreased after 1 year.
Signs Iris Bulbs Are No Longer Viable
How can you tell if stored iris rhizomes are still healthy enough to replant? Here are a few key signs that indicate an iris bulb is dead or no longer viable after extended storage:
- Very shriveled, dried out rhizome
- Lighter weight than healthy rhizomes
- Soft, mushy, or moldy
- Foul odor
A healthy iris rhizome still feels firm and has a smooth, intact outer skin. It may be slightly shriveled but still substantial and heavy for its size. Any excessive softness, mold, or foul odors indicate rotting and lack of viability.
Replanting Irises After Storage
When ready to replant stored iris rhizomes, follow these tips for best results:
- Replant in late summer or early fall.
- Choose a sunny, well-draining location.
- Plant the rhizomes just shallowly under the soil surface.
- Space rhizomes 12-24 inches apart.
- Water thoroughly after planting and as needed until winter.
- Resume watering when new growth appears in spring.
- Apply balanced fertilizer a few weeks after spring growth starts.
Even if the rhizomes look shriveled after long storage, they can regenerate after replanting. Monitor for new foliage in the spring. If no growth appears after 4-6 weeks, the rhizome likely didn’t survive storage. Healthy, robust leaves signal the iris has successfully come out of dormancy.
Storing Iris Bulbs Over Winter
In zones where irises are winter hardy, you can also leave the rhizomes in the ground and mulch over them. However, in zones with very cold winters, it’s best to dig them up in fall and store them using the same cool, dry methods described above until ready to replant in spring after chance of freeze has passed.
Whether storing over summer or winter, providing conditions that prevent the rhizomes from freezing, rotting, or dehydrating will maintain their health and growth potential when replanted.aiming for storage durations under 1 year is ideal.
Considerations for Different Iris Types
There are several different iris species and hybrids. Some have particular storage requirements:
- Bearded irises – Can be stored dry or planted temporarily in pots of damp sand. Avoid storing wet.
- Siberian irises – Fleshy roots prone to mold if stored wet. Keep dry.
- Japanese irises – Store dry or in very slightly damp peat moss or vermiculite.
- Dutch irises – Need dry storage only.
- Louisiana irises – Can be stored dry or wet. Often overwintered outdoors in pots submerged in ponds.
When in doubt, err on the side of storing iris rhizomes dry rather than wet to prevent rotting. Monitor all stored bulbs regularly and discard any that show signs of mold or decay before replanting.
Storing Iris Seeds
In addition to rhizomes, seeds can also be collected from iris blooms. Iris seeds have a very hard outer coat and can survive several years when stored properly.
For best longevity, iris seeds should be kept cool and very dry. Place seeds in an airtight container in the refrigerator or freezer for storage periods of 1-3 years. For long term storage of 5 years or longer, the seeds can be frozen or freeze dried.
Stored iris seeds that are still hard and white have the highest viability rates. Discard any seeds that are mushy or green-tinged as they have likely died and will not sprout.
Conclusion
With proper dry, cool, and dark storage conditions, most types of iris bulbs can be kept out of the ground for up to 1 year before replanting. For best results, aim to replant the rhizomes within 3-6 months after digging them up. Replant iris rhizomes in late summer or fall in zones where they are winter hardy. Monitor for new spring growth and signs of deterioration after long term storage. Stored correctly, iris bulbs can retain enough nutrients to flourish again when returned to soil.
