Unplanted bulbs are essentially a plant’s compact, self-contained food and growth storage organ, designed to survive a period of dormancy until conditions are right for growth. Correctly storing these bulbs is necessary to maintain their viability and ensure they bloom next season, particularly for varieties that cannot tolerate freezing temperatures in the ground. The goal is to induce and maintain a deep, stable dormancy, which prevents premature sprouting or decay before the proper planting time arrives. Improper storage conditions, such as excess moisture or incorrect temperatures, can quickly lead to desiccation, rot, or a compromised internal structure.
Preparing Bulbs for Long-Term Storage
The first step in successful long-term storage is a meticulous preparation process that occurs immediately after the bulbs are lifted from the soil or purchased. Begin by gently removing any large clumps of excess soil adhering to the bulb or tuber structure, using a soft brush or your hands. It is generally best to avoid washing the bulbs with water, as introducing moisture before storage can increase the risk of fungal infection and rot. If washing is unavoidable, the bulbs must be thoroughly dried immediately afterward.
After cleaning, inspect each bulb for damage, such as cuts, bruises, or soft spots, which indicate potential disease. Discard any bulbs showing mold, mushy texture, or mechanical damage immediately to prevent the spread of infection. Healthy bulbs must then undergo a curing period to harden the outer layers and allow surface moisture to evaporate. Curing involves spreading the bulbs in a single layer in a warm, dry, and well-ventilated location (60°F to 70°F) for a few days to a couple of weeks, depending on the bulb type.
Essential Environmental Conditions for Dormancy
Successful dormancy requires maintaining a stable environment, focusing on specific temperature and humidity levels for the bulb type being stored. Bulbs are categorized into hardy and tender varieties, and their storage needs differ significantly. Hardy, spring-flowering bulbs like tulips and daffodils require cool storage (35°F and 45°F) to satisfy their cold requirement for blooming.
Tender, summer-flowering bulbs such as dahlias and gladiolus require cool but not freezing conditions, typically stored between 40°F and 50°F. Some tropical varieties prefer a warmer 50°F to 60°F range. The storage area must maintain moderate humidity to prevent shriveling while ensuring excellent air circulation. High humidity encourages mold growth, while overly low humidity leads to desiccation and loss of viability.
A non-heated garage, cool basement, or root cellar often provides the necessary temperature stability and darkness. For smaller quantities of hardy bulbs requiring cold, a dedicated refrigerator can be used. Keep them away from ethylene-producing fruits like apples, which can inhibit flower formation.
Choosing Storage Materials and Containers
The materials used for packing and containing the bulbs are important for ensuring air exchange and preventing moisture buildup. Containers must be breathable, meaning airtight plastic bags or sealed bins that trap moisture and lead to rot should be avoided. Recommended options include sturdy mesh bags, paper bags, cardboard boxes, or wooden crates, all of which allow for necessary air flow.
Inside these containers, a packing medium is needed to insulate the bulbs, maintain a consistent micro-environment, and prevent contact, which minimizes disease spread. Suitable mediums are slightly insulating and moisture-absorbing materials, such as:
- Dry peat moss.
- Vermiculite.
- Clean sawdust.
- Shredded newspaper.
For many tender bulbs, the packing medium should be kept only slightly moist to prevent the large fleshy tubers from completely drying out.
When packing, ensure the bulbs are layered with the chosen medium so they are not in direct contact. Never stack them more than a few layers deep to avoid excessive pressure or heat generation. Labeling the containers with the variety, color, and date of storage prevents confusion when planting time arrives and aids in maintenance checks.
Monthly Inspection and Maintenance
Storage requires regular, active monitoring to ensure the bulbs remain healthy throughout dormancy. A monthly inspection is recommended to check for changes in condition. Look for signs of decay, such as soft, mushy spots, or the presence of mold (typically white, gray, or blue-green fuzzy growth).
If a rotten or moldy bulb is found, remove it immediately to prevent the fungal infection from spreading. If the batch appears shriveled, the packing medium may be too dry, requiring a light misting or slight increase in humidity. Conversely, widespread mold indicates the storage area needs better ventilation or the packing material is too damp.
Premature sprouting occurs if the storage temperature is too warm or fluctuates, breaking dormancy too early. If a bulb begins to sprout, move it to the coolest available location without freezing to slow growth, or plant it immediately in a container indoors.
A bulb should be discarded if it is completely soft, heavily covered in mold or fungus, or dried out to the point of being rock-hard and brittle. These conditions indicate the storage organ is dead or beyond recovery.