HAND POLLINATING DAHLIAS

by Wayne Holland


(originally published by the Puget Sound Dahlia Association in "Dahlias of Today" 1995) revised Dec.96 Information from

Jean Knutson : 7335 34th Ave. Southwest : Seattle, WA 98126


Most of the large dahlia hybridizers let the bees do their pollinating for them, although they do tend to isolate and plant varieties of interest together. The benefits of this type of planting are many:

 

The downside is that only one parent is known for certain, and in my experience I have also found a much lower proportion of double flowers. With hand pollination at least 50% of your resultant offspring can be double. Usually much more!

The small home garden hybridizer just doesn't have room for a lot of poor seedlings. On the other hand he or she can provide the daily attention that will yield specific crosses for specific goals and a high proportion of double blooms.

DAHLIA ANATOMY

Examination of a dahlia bloom that has run out of petals will show the reproductive parts of interest to the hybridizer. Each of the many central disc parts is composed of tightly fused and unopened stigmas. These pick up the pollen bundles from anthers hidden inside of the capsule from which the stigmas emerge. These then shed the ripened pollen from the outer sides of the fused structure, and, when the pollen is gone, the fused pair of parts opens, exposing the ripe stigmatic inner surfaces which are prepared to receive incoming pollen. This design ensures that self-pollination does not occur. There are other barriers to prevent pollen from the same flower or other flowers on the same plant from accomplishing pollination, but my experience has shown that, for some varieties at least, self-pollination between disc florets can happen. Luckily, foreign pollen from your deliberately chosen parent does seem to be more vigorous and will take precedence if it is compatible at all.

To cross two dahlias is quite easy, but be prepared for the occasional failure, as some cultivars are very incompatible and also because you and I are not as skilled as bees. Furthermore, genetically related varieties are often so similar that Nature's safeguards against self pollination, which are chemically or hormonally based, may operate to prevent pollen germination and drastically reduce fertility. Sometimes a reverse cross may succeed and it is worth a try, but pollen is not always readily available from some dahlias. Thus inbreeding or line breeding may produce few seeds. The usual advice to improve your chance of success is to use cultivars that have the characteristics that you desire, but are probably not related. However, do try any cross that suits you as you will often get some seeds.

The 1990 Vancouver Dahlia Society best seedling, HY CINNAMON (MFD Dark Blend of red and pastel orange) came from a seed head with ONE seed. BITSA (pollen) onto GLENBANK TWINKLE[ PHOTO ]. Four or five attempted crosses should yield two or three seed heads with up to a dozen seeds each, and since a small grower has limited garden space, that is enough. Seed from a good year's crosses will last for at least two years; some growers believe seed often germinates better in subsequent years.

Choose your seed parents carefully and with a specific goal in mind. Remember to include such things as tuber quality, disease resistance and foliage characteristics and color as you screen potential seed parents. If you are working to improve ball dahlias, start with good ball dahlia parents. Don't use inferior varieties and hope to get good results. It's best for the small gardener to work to improve one area of dahlias rather than using a shotgun approach.

Observation will show that some dahlias produce lots of pollen and some produce hardly any, so choose accordingly.

Pollinating Dahlias

As a pollen bearing (male) parent starts to show its center, cut it with a decent stem and carefully pluck off all petals. Put it in fresh water in a cool window and wait for lots of good dry pollen to form. Keep the window closed to prevent bees from stealing and also from contaminating your pollen. The female bloom that is to receive the pollen must be selected as its center opens, but before any of the fused disc florets have separated and been pollinated. Carefully pluck off all the petals (Be sure to get ALL of the petal!) and cover the future seed head with some kind of hood. A nylon stocking toe works well.

Now for the actual hybridization. When the hooded female has developed a good number of opened stigmas[ PHOTO ], remove the hood and simply, but gently, push the pollen laden male bloom into the ready stigmas. Brush gently and slowly in several directions. Cover again at once. Repeat, at least daily, until the stigmas begin to brown and shrivel. At this time it is a good idea to spray some Benomyl into the seed head to prevent rot (I add a touch of Captan also). Very careful petal plucking will reduce potential rottable parts, but so much pollen will have been added by your efforts that rot is always a danger. Many people "milk" the pod to squeeze out excess fluids and decaying pollen. Leave covered for 3 or 4 more weeks (or as long as possible if late in the season) and then cut with a stem and bring indoors to a bright location. The seed head is definitely harvestable when it has turned from green to straw colored. Leave in water if you think that more time is needed to ripen the seeds. Eventually the seed pod will dry and can be gently taken apart to find the seeds. They will be dark grey or black and of various thicknesses and widths. Keep them all! Cool and dry is best. An envelope is a good storage container. Label it with the female parent listed first, and the pollen parent(s) second. Perhaps more than one possible pollen parent was used if you needed the pollen or wanted to improve your chance of success.

Planting in mid March is early enough. Transplant the fairly large seedlings soon after they germinate into individual small pots or multiple containers. Then later into larger pots as required. Grow them as COOL AND BRIGHT as you can to keep them stocky and move them out into a coldframe by mid May. In early June they can be planted out 18" apart in rows with posts at each end and twine for support in between. Don't stop them! Don't overfertilize them! Let them grow straight up and bloom. Cull open centered or undesirable plants as soon as you can bring yourself to do so to give the better ones more space and light to make tubers. Varieties that survive should have the side branches disbudded in the usual way so that further decisions about bloom quality and competitiveness may be made.

A cross that yields good results can be repeated in other years, since you are in control - not the bees. Good luck ! Definitely a part of it all, but the rich genetic tapestry of the dahlia saves its best rewards for careful choice based on intelligent observation.

You might also be interested in another cross. Jean M and Ferncliff Fantasy, which I have been crossing for several years now, looking for a seedling that has the recurved elegance of Jean M[ PHOTO ], but with a color that is more interesting. Thus the choice of the brilliant Ferncliff Fantasy as pollen parent.

Wayne Holland

email to nospam_hydahlia@shaw.ca just delete the nospam part!

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