Barry Davies (breeder of the Barbarry range of dahlias)
Amateur dahlia hybridises are neither scientists nor botanists and the only way that we can gain our limited knowledge is through reading, listening and observation. Dahlia breeders and enthusiasts will always be indebted to the great geneticist W.J.C. Lawrence for his unravelling of the mystery behind the origin and the hybrid make up of the cultivated dahlia. Through his work we can see that which gives the cultivated dahlia its uniqueness among flowering plants, our favourite flower is a hybrid octoploid species with 64 chromosomes being derived from the hybridisation of two tetraploid species both with 32 chromosomes. The chromosomes are microscopic elongated bodies found in the nucleus of every living cell and are known to be the carriers of the units of heredity, the genes.
In the cultivated dahlia self incompatibility is the rule, which means that the dahlia is maintained in a highly hybrid state, self incompatibility is the phenomenon where although the pollen and ovules are good no seed is set when a flower is pollinated with its own pollen. It therefore follows that every seed obtained from the modern dahlia will produce an unique new variety and through constant selection the dahlia breeder hopes to create something worthwhile. Most colours or combination of colours with the exception of blue and black can be seen in the cultivated dahlia. White tipping is not passed on in the usual genetic way but by the maternal parent, therefore if this characteristic is required select seed from the flower head showing the most white tipping.
So you want to raise dahlias? The easy way to achieve this goal would be to purchase seed form a well known dahlia nursery or hybridiser, you would then have to gamble that your source of seed is letting you obtain the same strain that they themselves use to get their own new worthwhile originations. Personally even if you did hit the jackpot it would be a hollow triumph because it would always be someone else who had actually done the creative side of your success. It is almost certain that like so many other hybridisers I will never create a new dahlia that is way ahead of its time and sets the world on fire. Never-the-less it always gives me great satisfaction when my originations are described as having typical Barbarry growth habit and flower formation. This is not to say that the person describing this growth-habit and flower formation thinks that it is of a superior merit it is just that they seem to acknowledge that I am working to a system or plan.
What ever system or plan, that you decide upon, you have to be able to walk the walk as well as been able to talk the talk. By that I mean that when you have got the theory worked out to your satisfaction you have to have the stamina and the dedication to put it into practise. The world is full of people who can talk a good dahlia but the really great hybridisers and exhibitors get their hands dirty and quietly get on with the task in hand. What ever goal you set yourself it is important to have the knowledge and skill to know the attributes that a worthwhile new dahlia must have. If you are the kind of person who is spurned on by failure and false dawns read on but remember that with most plans because of the time scale you may only get one shot at it.
The first step that I took was to decide which classifications to specialise in, with my heavy land I decided to concentrate on small and miniature decorative and ball dahlias which were already growing well for me. Because I did not want to produce a load of mongrel crosses between semi cactus, decorative and ball dahlias I discarded all my stock of the former. To increase the diversity of my gene pool I purchased stock of any decorative and ball variety that had attributes that I wanted in my seedlings, avoiding like the plague any variety that had any history of virus problems.
Year one saw me planting all these standard decorative and ball dahlias into my dahlia plot which was divided into two with one half for small flowered dahlias and one half for miniatures, I let the bees pollinate the flowers and I collected the seed. There were two schools of thought at this point as to how to proceed, one was to start keeping records as to the possible seed parents, the other was to use my own intuition. I am of the opinion that people who keep good records about dahlia breeding just end up keeping good records and over complicate the procedure.
Year two saw me planting all the same standard varieties plus the seedlings that had germinated form the previous years saved seed, it was an exciting time seeing and evaluating these seedlings. This is also where the learning process begins and assessing the merits of seedlings is always a fine balancing act between being too armoured and being too critical. Seed was harvested from the standard varieties again and the tubers saved from the selected seedlings.
Year three saw me planting all the standard varieties, the new second year tubers and also the seedlings produced from the previous years seed. When evaluating the second year tubers it was the first of many disappointments to discover that I had been too armoured the previous flowering season and only about a dozen tubers would be worth keeping to have plants propagated from. I again marked any potentially good seedlings and harvested seed from the standard varieties.
Year four saw me planting all the standard varieties, the plants produced from cuttings taken from the now dozen third year tubers, the second year tubers and the seedlings from the previous years seed. You may now see that a production line is starting to take shape and we have many new dahlias in different stages of development. Seed was harvested from the standard varieties and the plants from the third year tubers that had again survived a further cull. The second year tubers were judged and the best retained along with the new seedlings which had shown potential.
Year five was where I decided that click-ability had occurred and all the worthwhile genes from the standard varieties were now present in my new dahlias. It now seemed logical to me that in order to keep moving forward I had to dispose of all the standard varieties for good and hence forth only grow and use as seed parents my own new varieties. It was also my practice that when I disseminated a variety, so as to keep moving forward I would not grow that dahlia again, that is why keeping records of crosses would have been of no benefit with this system.
Because of the fact that I had started with a very large gene pool, even after all these years of inbreeding I have not lost vigour in my dahlias or had virus problems. One mistake that I did make however was that I was too busy trying to improve formation with the result that I forgot about the importance of colour. This resulted in my dahlia plot being dominated by cold colours, mostly reds, pinks and purples. To get back to a balanced colour range proved to be a long task, I had to wait for whites and yellows to occur in my seedlings and practice positive discrimination in their favour until a better colour range was achieved.
After all that theory a few words on the practical side may be of help to some readers, dahlias produce various types of seed pods that need treating in different ways, some pods do not completely close and need harvesting early while some flowers are reluctant to loose their petals and need to be visited two or three times in order to remove them. I have never indulged in that horrid messy practice of milking seed pods which involves squeezing the pods to removed so called access sap. Sometimes I may harvest late immature seed pods complete with foot stalk and keep them stood in tubs of water for a few weeks in the hope that the seed will mature.
In normal years I usually start gathering seed pods as they mature in late September and lay them out in trays on the greenhouse benches to dry. The pods are opened at my leisure, choosing the ones that may be damaged or starting to turn brown first. Fully mature seeds are dull brown but dark purple seed is the norm for me and should stay viable for many years if stored correctly. The seed-head contents are placed into trays and allowed to dry out naturally, keep turning this combination of seed and husk so that fungal problems don’t occur. If you have a fine day with a gentle breeze place the trays outdoors and as the contents dry rub them together gently in your hands to separate the seed from the chaff. Find a tray that you feel comfortable with and using both hands gently toss the contents of the seed pods into the air. The chaff will drift away while the heavier seed falls back into the tray. Alternately if you are a masochist you could, as some experts recommend pick the seed out of the pods one by one.
We now need to get the seed bone dry before we attempt to store it. My method is to place all the seed into a large jam making pan which is taken indoors into a warm room for a couple of days. Stir up the contents a couple of times a day until you are certain that the seed is completely dry, I then put the seed into a large tin which is then stored in an unheated garage.
It’s now springtime and we are quietly confident that amongst the few thousand seeds that we have saved there is a world beater. The major problem facing us now is that in order to ascertain which seed it is we have to grow and flower them all. We have to keep our fingers crossed that during this process our world beater is not the seed that does not germinate, the plant that gets eaten by a slug or any plants which succumbs to the many other perils lurking in the garden.
I sow my seed quite thickly in trays containing the Barbarry Mix, three parts grit sand, one part vermiculite and one part perlite. Cover the seed with grit sand, water well and place on a heated bench, this spring three year old seed took four days to germinate and it has got the appearance of 100% germination. Once the seed has germinated I henceforth water the trays with a half strength liquid feed, which is increased or decreased in strength depending on how plants are doing. Giving a watering with insecticide and fungicide will help to keep the plants healthy, any white or yellow seedlings should be removed as these lack the essential green pigment called chlorophyll.
With regards to pricking out and potting on etc. I have been there, done that but I don’t do it any more. The plants are left in the trays until planting time and then gently separated, planted out using a dibber and well watered in. The seedlings are planted six inch apart but in such a way that I can both reach and evaluate each plant when it produces its flowers. Any tiny plants can be potted up if you wish, into the same mixture and kept growing like pot tubers. These tiny tubers when planted the following year will give early flowering plants which is helpful if your area has a short flowering season.
In conclusion I would like state that to produce new dahlia varieties of exhibition quality on a consistent basis takes a degree of knowledge and skill, to get that elusive world beater we also need good fortune.
Happy gardening, Barry.