How to Choose, Plant and Care for Bulbs, Tubers, Rhizomes and Corms

While Bulbs, Tubers, Rhizomes and Corms are collectively referred to as “bulbs”  there are major differences between them.

Horticulturalists call these “true” bulbs to differentiate them from the all the other types. True bulbs consist of layers of modified leaves and contain a miniature flower or sprout in the center — like an onion cut in half from top to bottom. The roots at the bottom of the bulb anchor the plant to the ground and absorb water and nutrients. Other examples of true bulbs include garlic, amaryllis, tulips, daffodils and lilies.

The most well-known tuber is the potato. Tubers can be easily recognized by the eyes from which the stems grow. These types of plants can be cut into pieces and re-grown as long as each piece contains an eye. Other examples of tubers include dahlias and caladiums.

Rhizomes are simply fleshy underground stems. They grow underground or right at ground level with many growing points or eyes similar to potatoes. Common examples of rhizomes include canna lilies, bearded Iris, Ginger and bamboo.

Corms look like true bulbs but do not have layers of modified leaves but rather they are solid. As the leaves and flowers grow, they absorb the nutrients and the corm shrivels up and disappears. One or more additional corms are produced through the growing season and that’s how the plant regenerates itself. Examples of corms include crocus, Gladiolas and tuberous begonias.

Selecting and Planting Spring-Flowering Bulbs

Spring-blooming bulbs should be planted in the fall as soon as possible after they are purchased. Buy the largest, firmest bulbs available. Cheap bulbs usually produce weak plants with few or no flowers. Avoid bulbs that have mildewed, fungus, or are blackened or squishy. Payne’s takes great pride in offering only the highest quality bulbs.

Preparing A Bulb Bed
Most bulb plants need well-drained soil and at least 6 hours of direct sun a day.

  1. For new beds, remove the top six to ten inches of soil from the area to be planted. Set the soil aside.
  2. If burrowing rodents are a big problem in the area, line the floor and walls of the bulb bed with fine-gauge wire mesh.
  3. For already well-drained sites, mix the set-aside soil with equal amounts soil conditioner.
  4. If the soil is heavy clay, blend 1 part set-aside soil, 1 part soil conditioner, and 1 part pumice or crusher fines. (Do not use fine sand or the hot summer sun might make adobe of the bed.) If drainage is very poor, consider making a raised bed, using rot-resistant planking to raise the bed 1 foot minimum above the surface of the surrounding soil.
  5. Backfill the excavated bed with one of the above mixtures. If the bed ends up looking somewhat mounded, don’t worry; it will settle in time.
  6. Broadcast some powdered rock phosphate over the bed surface (follow the directions on the bag of phosphate). This will provide the bulbs with the phosphorus they need for good flower formation in years to come. Dig the phosphate thoroughly into the top foot of the bed soil.
  7. Water the bed thoroughly and wait at least a day before planting.

Arranging Bulbs In the Bed
Bulbs look much better planted in clumps rather than rows. For a naturalized look, consider tossing bulbs at random into a bed and planting them where they land. It’s also fine to plant bulbs among existing shrubs and perennials. Those who reserve a separate bed for bulbs should leave space between bulb-groups for plugging in annuals the following spring, which will grow up and help mask the aging bulb foliage as summer progresses. Important: Regardless of how they are arranged in a bed, bulbs must never touch, as this can encourage the spread of fungus rot diseases.

How Far Apart and How Deep?

Large bulbs, such as tulips, daffodils, hyacinths, and lilies, should be placed 4-6″ apart and 8” deep. Iris rhizomes  should be planted half-buried in the soil or just below the soil line (they like to bake in the summer).

Smaller bulbs, such as snowdrops, grape hyacinths, crocuses, lily-of-the-valley and dwarf irises, should be planted 2-3″ apart and 4-5” deep.

Plant bulbs bottom-side down and tip upward.

Firm the soil over the newly planted bulbs and water them in thoroughly once, then leave them alone until spring.

Springtime Care of Fall-Planted Bulbs
When the bulbs emerge in spring, sprinkle some organic, slow-release fertilizer over the bed. Water deeply once a week throughout the growing season.

Autumn Care of Fall-Planted Bulbs
Once bulb flower petals start to fade, remove the flower parts with a sharp scissors so the bulbs don’t set seed. If bulbs are permitted to go to seed, they’ll tend to put all their strength into forming pods instead of underground offsets, and the mother plant will likely die.

Do not remove the flower stem or any aboveground parts of the plant as long as they are still green (green means the plant is still storing sunshine for next year). Once most of the bulb plant’s top growth has died, cut it off and compost the refuse.

Dividing and Replanting Spring-Blooming Bulbs
The best time to divide and replant spring-blooming bulbs is immediately after they have completed flowering. However, this may be done any time up to early September. If dug and replanted later than the second week of September, spring-blooming bulbs may not have enough time to develop a solid root system before frost. To divide and replant bulbs:

  1. Prepare the bed where they are to go before digging them.
  2. Choose only the healthiest roots.
  3. Trim any leaves to 6″ long before replanting them.
  4. Dig down deep enough so that the bulbs’ root systems will not be damaged.
  5. Transfer the dug plants to the new location immediately and plant only as deep in the ground as they grew before.
  6. Water in thoroughly.