Divide and Plant Spring Bulbs

Are you thinking about dividing or planting bulbs now, in preparation for next spring?

I must insert the obligatory reminder that we often use the term “bulbs” to refer to true bulbs, as well as corms, rhizomes and root tubers, i.e., all plants with underground storage organs. Collectively, such plants are correctly called geophytes.

This is the season for dividing and planting spring-blooming geophytes. Dividing can be done annually, but is done most efficiently on a three-year cycle because in that time they can become too crowded to bloom well.

Daffodils are among the first of the geophytes to finish their cycle: their leaves have dried and dropped by July. If the leaves are still on the ground, the location of the bulbs will be evident. Otherwise, digital snapshots taken when the leaves are still green will provide useful clues of their locations. Plant daffodil and other bulbs about three times as deep as the bulbs’ diameter.

Irises should be divided and planted during the period from July through September. This year, the Monterey Bay Iris Society’s annual rhizome sales will be on August 4th at Deer Park Center and August 11th at the Aptos Farmer’s Market. For details, visit http://www.montereybayiris.org. Plant iris rhizomes shallowly, with their top surfaces exposed to light and air.

The tall bearded iris is the most popular variety of iris, but there are several other interesting species in the genus Iris, and many hundreds more in the iris family.

Another popular geophyte, the Gladiolus, should be divided in the fall, after the leaves have turned brown. Watch for gladiolus rust, a fungal plant disease of quarantine significance that first appeared in northern California in 2010. This disease is associated with the Gladiolus, but it also affects other genera in the iris family (Iridaceae): Tritonia, Crocosmia and Watsonia.

The fungus’s botanical name, Uromyces transversalis, provides a clue to its identification: pustules on both sides of the leaves tend to run across the width of the leaf, i.e., transversely.

If you spot these symptoms in your garden, seal the entire plant, corms, stems and leaves, in a plastic bag and discard it in the green waste (not in your compost bin). If gladiolus rust doesn’t appear in your garden, consider yourself fortunate.

Commercial growers can use systemic fungicides to control gladiolus rust, or to salvage the corms of infected plants, but these are toxic chemicals not suitable for use in residential gardens.

When dividing and replanting your healthy “glads” plant the larger corms six-to-eight inches deep, to reduce or eliminate the need to stake the plants.

Preparations at this time of the year will yield a delightful display in the spring.

Enjoy your garden.


Here is an example of gladiolus rust, showing the pustules arrayed across the leaf’s surface. This pattern is not always this clear. For other examples, search Google Images for “gladiolus rust.”

Gladiolus Rust

This fungal infestation deserves some concern, but it might not appear in your garden. Unless and until it does, the need to divide your geophytes when they get crowded, or to add new plants to your garden, is a higher priority.

When dividing geophytes, a garden fork is easier to use and less likely to damage the plant, compared to a garden spade. The task also is easiest when the soil is fairly dry and will fall away readily from the bulbs, corms or rhizomes.

Separating bulbs and corms is relatively obvious, but separating iris rhizomes is more involved. With each season, the original rhizome produces new rhizomes, which grow out like a new generation. After three years (when dividing is needed), there will be a cluster of rhizomes, which each new generation growing out of the previous generation. Snap the rhizomes apart and discard the older generations. The youngest generation of rhizomes will produce new plants.

Digging rhizome

1. Dig the entire clump gently out of the ground with a spading fork or shovel.

Dividing the New and Old Rhizomes

3. Cut off the outer rhizomes. Discard old center portion without leaves. Cut out any signs of rot and dust with fungicide as a precaution.

Planting Rhizome

4. Plant each division as shown by pressing the rhizome into a mound in the planting hole, with the top of the rhizome almost at soil level. Fill in and firm the soil.

2 thoughts on “Divide and Plant Spring Bulbs

  1. I planted a bed of Gladiolus from bulbs I got at Costco last spring. I got around to planting them late, but they are finally blooming. Unfortunately, a the same time the blooms came out, so did the rust. I want to enjoy the blooms, but I have Irises, various lilies, and Agapanthus all growing nearby. Are these other pants in danger of being infected? Did the fungus come along with the bulbs? They were imported from Holland I believe.

    • Gladiolus rust (Uromyces transversalis) originated in South Africa and first appeared in California in 2006. It is a plant disease of “quarantine significance,” and the subject of a national management plan by the U.S. Department of Agriculture. Gladiolus rust affects only plants in the Iridaceae family, that includes over 2,000 species, including Tritonia, Crocosmia, and Watsonia. That family includes Irises (mentioned as being nearby in your garden) but not Lilies or Agapanthus.

      Gladiolus rust can be controlled with weekly spraying of a systemic fungicide such as Benodanil or Oxycarboxin, but these might be products available only to commercial growers. Check your local garden center for an appropriate fungicide for residential use. You might find Rose Shield or Fungus Gun. Both of which contain a systemic fungicide called Myclobutanil.

      The fungus probably arrived in your garden along with the corms. Many are imported from Mexico, but Costco’s shipment could have come from Holland, as you indicated. The fungus has been in Europe since 1876.

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