Hybridization

Hybridization is the result of cross pollinating and is also know by the term 'Crossing'. The term Crossing will also be used in this section.

 

There are many reasons for hybridizing (cross pollinating) penstemons, not the least of which is the creative activity in developing something new. In addition, hybrids are sometimes more satisfactory garden plants and better adapted to your garden conditions because they have genes for adaptation from different sources. You may produce hybrids more adapted to your own climate and site by crossing species from mild climates with ones that do well in your garden. However, some hybrids are intermediate between parents and may be poorly adapted to garden use.

 

Hybrids do occur in the wild where species are within the same range and in the same subgenus; for example, the Dasanthera section. The Dasanthera species that commonly hybridize with each other include P. fruticosus, P. davidsonii, P. barrettiae, and P. rupicola. They are closely related and have the same pollinators so the chances are very good that the pollen of one species will be transferred to the pistil of another species. Less common are hybrids in other sections where the species are not in close proximity or closely related. These have been created in most cases by someone deliberately bringing the plant together to achieve crossing.

 

One of the first decisions to make in a penstemon breeding program is to determine which penstemons you want to use as parents and what results you want to achieve. It may be to create a shorter form, a hardier plant or extended flowering. Hybridization is usually considered easiest with species that belong to the same subsection or section, but not always. Some of the best hybrids come from wide crosses.

 

The first step is to collect pollen from species or hybrids that will be used as the male parent. The pollen is collected on a cotton pipe cleaner from flowers that have very recently opened. Anthers may also be collected by a tweezers and placed into a small vial if it is to be preserved for later use, in which case it should be refrigerated. To be sure that it has not been contaminated with pollen from another species by wind or a visiting insect, some breeders collect anthers before they open and place them in a warm and protected location until they have shed their pollen, which is then refrigerated.

 

Removing the anthers from a flower and placing them in a vial for future use

 

The flowers to receive pollen are prepared by removing the anthers, staminode and petals, which is usually done just before the flower opens. This is called emasculation. The penstemon flowers to be pollinated must have the petals and anthers removed.

 

This is easy to do by grasping the sepals with the fingers of one hand and with the fingers of the other hand gently clasping the lower side of the outer end of the bud and pulling it forward.

 

The petals, staminode and anthers come off together because the staminode and fertile anthers are attached to the petals. What remains is the ovary, enclosed in the sepals, and the attached pistil (style with the stigma).

 

The pistil is usually not damaged in this process. The stigma (tip of the pistil) is usually not ready to receive pollen when the bud is first removed. It may be hours to several days before you can see the small sticky knob develop at the outer end of the stigma to receive the pollen. Insects will not visit a flower that has been emasculated, but to protect it from wind pollination, it can be enclosed in a small paper bag. The style will usually bend downward and a sticky knob will be visible when it is receptive.

 

It may be receptive for several days. The pollen, from a nearby plant or that which has been saved previously and refrigerated, is applied generously on the receptive stigma of the female parent.

 

The pollinated flower should be labeled with a small string tag such as a jeweler’s tag, giving the name of the female parent, followed by an “x” and the name of the male or pollen donor species.

 

With successful pollination, the style withers and the ovary begin to swell. It will take approximately six to eight weeks, depending on species and weather conditions, for the seeds to ripen. The seeds should be collected after the capsule has turned brown, but before the capsule splits.

 

Once the seeds are dried and harvested, the information on the tag can be transferred to the seed envelope. Unsuccessful pollinations should be part of the records you keep, also.

 

When the seeds are grown out, some of the resulting plants will look like one of the parents and some may be intermediate. Sometimes the combination of genes does not visually show up in the first generation. Therefore, it is worthwhile to collect seed off of the progeny and grow this seed out and look for new types of plants in the next generation. It may also be worthwhile to pollinate some of the progeny and grow future generations of the first cross as well as later ones since some characteristics may not show in the first generation. This can be a very exciting aspect of growing penstemons if you have patience!

 

For those desiring more details on breeding penstemons, we recommend the book entitled, “Breeding Ornamental Plants”, edited by D.J. and M.B. Callaway, from Timber Press, published in 2000. It has a chapter on penstemons. One of the best examples of hybridizing plants is the work done by Bruce Meyers, a deceased member of the American Penstemon Society, in producing the Mexicali Hybrids.