For gardeners in temperate climates, the vivid displays of Dahlias, Gladiolus, Cannas, and Begonias are highlights of the summer garden. Unlike their hardy spring-flowering counterparts (like tulips and daffodils) that can brave freezing temperatures underground, these vibrant beauties are categorized as “tender” bulbs (or corms, rhizomes, and tubers, collectively referred to as bulbs for simplicity). Hailing from warmer climates, they lack the natural cold hardiness to survive frigid winter soils. To enjoy their spectacular show year after year, these tender treasures must be lifted from the ground and stored indoors over the winter months.

While the prospect of digging up and storing bulbs might seem like an arduous tasks, it’s a relatively straightforward process that, once mastered, becomes a rewarding ritual. Proper storage ensures their survival through dormancy, protecting them from frost and rot, and guaranteeing a bountiful return next season. This guide will provide comprehensive instructions on how to successfully harvest, prepare, and store your tender bulbs over the winter, allowing you to preserve your precious investment and anticipate another glorious summer bloom.

What are Tender Bulbs and Why Store Them?

“Tender bulbs” is a broad horticultural term often used to describe any plant with an underground storage organ (bulb, corm, tuber, or rhizome) that cannot tolerate freezing temperatures.

  • Examples of Common Tender Bulbs:
    • Dahlias (tubers)
    • Gladiolus (corms)
    • Cannas (rhizomes)
    • Begonias (Tuberous) (tubers)
    • Caladiums (tubers)
    • Calla Lilies (rhizomes)
    • Elephant Ears (Colocasia, Alocasia) (tubers/rhizomes)
  • Why Store Them: In USDA Hardiness Zones where the ground freezes (generally Zone 7 and colder), these plants will perish if left in the soil over winter. Lifting and storing them provides them with the warm, dry, and protected environment they need to survive dormancy and be ready for replanting in spring.

Nairobi Context: Nairobi’s climate is warm year-round and does not experience freezing temperatures. Therefore, tender bulbs generally do not need to be lifted and stored over winter in Nairobi. They can typically be left in the ground as perennials, blooming annually. The “winter care” for these plants in Nairobi would focus on adapting watering during the cooler dry season (June-August) or managing heat stress during the hotter dry season (January-February). This guide is primarily for gardeners in temperate climates.

When to Lift Tender Bulbs

Timing is crucial to ensure the bulbs have stored enough energy and are ready for dormancy.

  • After the First Light Frost: The ideal time is usually after the first light frost has killed back the foliage, but before a hard, deep freeze. A light frost signals to the plant that it’s time to prepare for dormancy and helps redirect energy from the leaves down into the underground storage organs.
  • Don’t Wait Too Long: Waiting too long (e.g., after the ground has frozen solid) can damage the bulbs and make them much harder to dig.
  • Foliage Dies Back Naturally: Allow the foliage to remain on the plant until it is naturally killed by frost or begins to yellow significantly. The leaves are still photosynthesizing and sending energy to the bulb.

Step-by-Step Guide to Lifting and Preparing Tender Bulbs

Different types of bulbs have slight variations in their preparation, but the general principles apply.

General Steps for Most Tender Bulbs:

  1. Cut Back Foliage: Once the foliage has been blackened by frost (or has yellowed significantly), cut the stems back to about 4-6 inches (10-15 cm) above the ground. This stem provides a handle and also helps you locate the bulb.
  2. Dig Carefully:
    • Use a digging fork or spade to gently loosen the soil in a wide circle around the plant, well away from the central stem to avoid damaging the bulb.
    • Pry up the entire clump of roots and soil.
  3. Clean the Bulbs:
    • Gently shake off excess soil. Avoid rubbing or scrubbing too hard.
    • For some bulbs (like Dahlias), you might carefully rinse them with a hose to remove most of the soil, ensuring not to damage the “eyes” (growth points).
    • Important: Do NOT remove any remaining fibrous roots or small rootlets at this stage.
  4. Inspect for Damage/Disease: Examine each bulb for any signs of disease (soft spots, mold, rot) or pest damage. Discard any bulbs that are soft, mushy, or heavily diseased to prevent the spread of problems in storage.
  5. Cure/Dry Thoroughly (Crucial Step):
    • This is perhaps the most important step for successful storage. Bulbs must be completely dry before storing to prevent mold and rot.
    • Place the cleaned bulbs in a single layer in a cool, dark, well-ventilated location (e.g., garage, basement, shed) for 1-3 weeks. Do not expose to direct sunlight or freezing temperatures during this process.
    • Air circulation is key. You can place them on screens, newspaper, or cardboard.
    • For Dahlias and Cannas, allow the remaining stem stub to dry and shrivel.

Specific Considerations for Different Bulb Types:

  • Dahlias (Tubers):
    • After curing, inspect the “eyes” on the crown (where the stem attaches) for next year’s growth.
    • You can divide clumps at this stage or wait until spring. If dividing now, ensure each division has at least one “eye” and a piece of the original crown.
    • Allow cut surfaces to “callus over” (dry and heal) for a few days before storage.
  • Gladiolus (Corms):
    • After digging, you’ll often see a new corm forming on top of the old, shriveled “mother corm.” Gently break off and discard the old mother corm and any remaining roots.
    • Keep any small “cormels” (baby corms) if you wish to grow new plants, though they may take a few years to flower.
  • Cannas (Rhizomes):
    • After cutting back foliage and digging, gently divide large clumps into smaller sections. Each section should have at least 2-3 “eyes” (growth points) for optimal replanting.
    • Ensure any cut surfaces are allowed to cure for a few days before storage.
  • Tuberous Begonias:
    • Lift the tubers with soil clinging to them, then allow the soil to dry and gently brush it off.
    • Cut the stems back to about 1 inch.
    • Cure for 1-2 weeks.

How to Store Tender Bulbs

Once cured, bulbs are ready for their winter slumber.

  1. Choose a Suitable Medium:
    • The storage medium should be light, airy, and absorbent to prevent moisture buildup and rot.
    • Recommended options: Dry peat moss, sawdust, vermiculite, perlite, shredded newspaper, or wood shavings.
  2. Select a Storage Container:
    • Use containers that allow for good air circulation, such as cardboard boxes, paper bags, mesh bags, or plastic crates with ventilation holes.
    • Do NOT use airtight plastic bags or sealed containers, as this can lead to condensation and rot.
  3. Layer the Bulbs:
    • Place a layer of your chosen storage medium at the bottom of the container.
    • Arrange the bulbs in a single layer, ensuring they don’t touch each other.
    • Cover with another layer of medium. Repeat layers, making sure bulbs are fully covered and separate. This prevents rot from spreading if one bulb goes bad.
  4. Ideal Storage Conditions:
    • Temperature: Store in a cool, dark, dry, and frost-free location.
      • Ideal range: $4^\circ \text{C}$ to $10^\circ \text{C}$ ($40^\circ \text{F}$ to $50^\circ \text{F}$).
      • Locations like a cool basement, unheated closet, or root cellar are often perfect. Avoid hot attics or very cold garages.
    • Humidity: Maintain moderate humidity. Too dry, and bulbs can shrivel; too moist, and they can rot. The storage medium helps regulate this.
    • Air Circulation: Good air circulation is crucial to prevent mold and mildew. Do not overcrowd containers.
  5. Labeling: Crucial for multi-bulb collections! Label each container clearly with the bulb type, color, and any specific variety names.
  6. Regular Inspection: Check your stored bulbs every few weeks throughout the winter.
    • Remove Any Rotted/Moldy Bulbs: Immediately discard any bulbs that show signs of mold, rot, or softness to prevent the spread to healthy bulbs.
    • Check for Shrivelling: If bulbs appear to be shriveling excessively, the storage conditions might be too dry. You can lightly mist the storage medium (not the bulbs directly) or add a small amount of slightly damp (but not wet) peat moss to the container.

What to Do in Spring

As spring approaches and the danger of frost passes:

  1. Gradual Awakening: Around 4-6 weeks before your last expected frost date, you can start to “wake up” some bulbs (like Dahlias or Begonias) by potting them up indoors in slightly damp potting mix. This gives them a head start.
  2. Replanting Outdoors: Once all danger of frost has passed and the soil has warmed sufficiently (typically when soil temperatures are consistently above $15^\circ \text{C}$ / $60^\circ \text{F}$), plant your tender bulbs back into the garden.

Final Thoughts

The effort invested in lifting and storing tender bulbs over winter is a small price to pay for the magnificent floral spectacle they provide season after season. This process ensures the longevity of your plants, protects your gardening investment, and offers the delightful anticipation of their grand re-emergence in the warmth of summer. By understanding the critical steps of careful digging, thorough curing, and proper storage in a cool, dry, and aerated environment, you can confidently preserve your precious blooms. Embrace this essential winter ritual, and your garden will continue to burst with the vibrant colors of Dahlias, Gladiolus, and other tender favorites year after glorious year.