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Writer's pictureJennifer McDonald

Ask a Master Gardener: The How and the Why of Dividing Bulbs

By: Mary Townsley, Mobile County Master Gardener |www.MobileCountyMasterGardeners.org

 

Thankfully, the heat and humidity of the summer are waning and the demands of keeping up with summer garden chores are easing. Nonetheless, there are fall tasks waiting. Notably, there is still time to divide those spring/early summer blooming perennial bulbs. 

 

What's a bulb?  We broadly use this term to refer to a diverse group of underground structures in which plants store food for the next growth cycle.  Despite their common purpose, these storage structures take different forms.

 

True bulbs are organized like onions. If you were to cut the bulb from stem to root, you'd see concentric layers of fleshy scales which are modified leaves. At the bulb base - where roots emerge - there is a basal growth plate where new bulblets can form. Each of these perennial bulbs or bulblets are complete plant packages! Amaryllis and narcissus have true bulbs.

 

Corms look somewhat like true bulbs from the outside but are modified stem tissue and solid inside. The nutrients in corms get used up producing flowers, so new plants come from cormels or cormlets growing at the old corm base. Crocosmia and gladiolus grow from corms. 

 

In contrast, irises and cannas grow from rhizomes, which are horizontal stems that grow at or near the planting surface. Rhizomes branch as they age, with roots and new shoots growing at the end of each branch.  

 

Tuberous roots, clustered at the base of the plant stem, form the storage structures for agapanthus and daylilies. These tuberous roots alone will not make a new plant - you need the stem base along with the storage root.

 

While tubers, such as begonia tubers, are also considered in this broad grouping of bulbs, we will leave discussion of tubers for another day.

 

We divide bulbs from clumps of perennial bulb-forming plants that have outgrown their allotted space in the garden or for which blooming has begun to falter. Division and replanting bulbs can rejuvenate flowering.  Some perennial bulbs, such as agapanthus, prefer a crowded environment so they may not flower the first year after division.

 

How to divide bulbs? Easier than long division...Spring blooming perennial bulbs are relatively dormant in the fall, though in our climate zone, many may retain green leaves until frost.  Divided bulbs should be replanted soon after division. Discard any that appear diseased - the bulb is mushy or there is evidence of borers. Specifics for division depend upon the type of bulb.

 

Division of true bulbs - amaryllis and narcissus - is easy.  Dig the clump, separate the bulbs and break off baby "bulblets" or offsets. If some of your amaryllis bulbs have become quite large, you can cut each into wedges. As long as you retain some of the basal growth plate in each section, these wedges will develop into new plants. 

 

Corms - particularly for crocosmia - are best divided in spring when you can detect the beginnings of new leaf growth from the top of the corm. Remember, old, depleted corms will not make a new plant, so discard these.

 

For rhizomatous plants - irises and cannas - retain rhizomes with new leaf shoots at the end and roots. Snap or cut off the lengths of old rhizomes to discard.  These old rhizomes will not make new plants.

 

For perennials with tuberous roots - agapanthus and daylilies - dig up the old clump. Tease the clumps apart or split the crown with a sharp blade if needed.  As the plant growth plate is at the base of the stem itself, make sure new divisions for replanting include a stem and roots.

 

Replant your divisions and prepare to enjoy new blooms in spring!





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