Hosta Propagation Method: Division Basics
The problem that commercial hosta growers face when trying to increase their supply of hostas is that hostas do not reproduce 'true' when grown from seed. That is, even if you use the pollen to pollinate and create seeds from the same hosta (self crossed), you may not get any seedlings that look like the parent! This curious genetic variability of hostas makes them more difficult to reproduce than most other perennials. For this reason, hostas are usually propagated by division, dormant bud cuttings, or tissue culture reproduction.
For the average hosta enthusiast, division remains the primary mechanism for propagating. In the traditional 'division' method, hosta plants are dug up and divided in the spring, when the shoots are still dormant. The least disruptive, but also least 'productive' method of division is to simply separate individual hosta shoots along with their associated roots. When replanted individually, these shoots will grow shoots of their own. It is currently believed that the third spring of growth is when the greatest number of new divisions are created by a hosta.
A more disruptive division method, dormant bud cutting, is sometimes used by gardeners to increase the number of resulting divisions. However, this more aggressive method also increases the risk of fungal contamination because it requires that the divisions be sliced up to encourage what would normally be dormant buds to actively grow and become whole shoots.
Iit is possible to simply 'slice' a piece of hosta plant off from the mother plant and plant it (making sure that the slice has some roots of its own). Think of slicing a piece of pie and you get the idea. Some small parts of the hosting crown and removed 'slice' will die off, but usually the slice will grow just fine as a whole new hosta plant. When slicing through crown material it is important that sterile tools be used as Hosta Virus X and other fungal infections can be introduced to the open tissue before the plants have a chance to heal themselves.
Hostas can be also divided in the fall. Quite a few people believe that leaves should be removed from hostas divided to reduce the loss of moisture. However, others believe that the plant will know when and if the leaf can no longer be supported and take the appropriate action by cutting off the nutrients to any leaves that it cannot support. So, you'll need to make your own decision about removing fully unfurled leaves when doing your divisions. However, everyone agrees that newly divided hostas should be placed in the shade shade whenever dividing after their leaves have fully expanded.
TECHNIQUES TO INCREASE THE NUMBER OF DIVISIONS
Because Hostas are relatively slow-growing perennials, there are typically not a large number of shoots that can be divided each year. This limitation has prompted some gardeners and researchers to try various methods in an effort to increase their hosta divisions.
- MOWING: One method commonly used to get as many latent buds to grow is to mow the hosta plant down to approximately 1/2 of an inch(!) during the summer growing season
- ROSS-IZING: Another method, pioneered by, you guessed it, a gentleman by the name of Ross, is described as "cutting through the stem just above the basal plate down through the basal plate to the roots and then making a similar cut at 90 degrees to the first, essentially quartering the plant in the late spring or early summer" (Ross, 1982, Zumbar, 1991). Additional shoots will develop at the cuts.
- CHEMICAL STIMULATION - Yet another way to increase the number of hosta divisions is to apply chemicals:
- benzyladenine, which is a cytokinin, has been the subject of quite a few published studies. Hostas that were treated with the chemical experienced an increase in offset formation, when the control subjects produced no offsets at all. However, this result is not consistent for all hosta cultivars.
- Keever, et al., (1995b) reported that the stage of development of the offsets resulting from cytokinin treatments affected the rooting of the stem cuttings. Those offsets with 2 or more leaves unfurled rooted more readily that those with less unfurled leaves.
- Cytokinin is a mixture of four structurally-similar substances that are found naturally in plants. For commercial purposes, cytokinin is purified from seaweed meal.
- N 6 benzylaminopurine has a similar affect as cytoknin.
- It is also known as BAP-10.
- N 6-Benzyladenine is a synthetic substances that is
similar to cytokinin in structure and its ability to enhance
growth in plants, however it is slightly toxic to aquatic organisms, and consequently is not
permitted to be used in or near bodies of water.
- In published test studies the presence of offsets at the time of N 6 benzylaminopurine application resulted in fewer offsets being produced when compared to plants that had no offsets at the time of application, so timing is more important when using this chemical.
Hostas are typically NOT propagated by seed for any commercial venture. This is because the seedlings seldom look like either parent, even if the seedling is a result of a hosta pollinating its own flowers. Because of this, sexual propagation of hostas is mostly done in wild populations and by hybridizers who wish to produce new cultivars. The downside to using seeds for hosta propagation is that it is rare for a seedling to be varigated. So chances are that if your hosta is striped in any way, it was not reproduced from seed! Even if both the pod parent and pollen parent are striped, most of the resulting seedlings will be solid green.TISSUE CULTURE
Tissue culture is the growth of tissues and/or cells separate from the organism. This is typically facilitated via use of a liquid, semi-solid, or solid growth medium, such as broth or agar. Tissue culture commonly refers to the culture of animal cells and tissues, while the more specific term plant tissue culture is used for plants.
Many new cultivars are propagated by tissue culture. A recurring criticism of tissue culture for hosta propagation has been the production of plants are produced that are not true to type and the older the culture gets the more likely there will be "sports". Meyer (1980) found that when 'Francis Williams', a popular cultivar, was propagated by tissue culture only 45% of the plants produced were variegated, with the rest being 45% a gold sport and 10% a green sport. These kinds of early results with tissue culture of hosta were discouraging and resulted in resistance to tissue- cultured plants in the market. In order to have a successful tissue-culture program with hosta it is important to be able to identify the form of the cultivar at roguing. The purchaser of tissue cultured plants should be able to evaluate the plants they receive to ensure the plants they invest in are true to cultivar. It can take 4 to 5 years before hosta taxa reach maturity of form and color (Armitage 1997). Establishing standards (plants known to be true to the cultivar grown to the same stage of development) to use to compare plants at different stages of growth in order to rogue several times through the production cycle is important. The source of the tissue to be cultured, florets, flower scapes, or shoot tips can make a difference in maintenance of parent plant characteristics, as can environmental treatments (Papachatzi, et al., 1981). Certain environments and production factors can affect the variegation or form of a plant in nursery production or in the landscape. A loss of variegation can occur in areas of high temperatures when nitrogen fertilizers are used (Armitage, 1997) causing plants to be mistakenly thought not true to type. Considering the precise and fastidious care required to propagate hosta in tissue culture the commercial success of this technique is a tribute to those propagators that produce vigorous, disease-free, true-to-name plants.
Tissue-culture techniques will continue to be refined by both large and small commercial laboratories to eliminate deviant plants from the production cycle and, ultimately, from getting to the consumer. Division will be the propagation method of choice for hosta, especially for small nurseries and specialty nurseries that sell a few plants of many different cultivars. It would seem that treatments and cultural practices that increase offset formation would benefit the propagator, the nursery grower, and the landscaper.
It would be interesting to know if commercial propagators and nurserymen have adopted the application of BA products to increase Hosta offset formation.
LITERATURE CITED AND OTHER RESOURCES:
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Aden, P. 1990b. Variegation and hybridization observations. pp104-118. In: The Hosta Book, 2nd ed. Timber Press, Portland.
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