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Hybrid Tree Dahlia Seed
Dahlia imperialis is the best-known Tree Dahlia in Northern New Zealand. It can grow to 3 or more metres in height and flowers briefly in May, usually coinciding with strong equinoxal winds. Its’ hollow stems frequently succumb. The most commonly seen form has large pendulous “pocket handkerchief” flowers. There is a double flowered white form as well as a single flowered white. The origin of both the pocket handkerchief form and double white remain a mystery. Accessions of D. imperialis from the wild have more normal, circular single blooms.
For over a century people have tried to cross D. imperialis with the hybrid garden Dahlia, D. variabilis in order to widen the colour range, to no avail. Two decades ago Dr Melanie Gatt undertook a PhD study looking at the cytogenetics of the genus Dahlia.
There are other species of Dahlia that have perennial aerial parts that are not hollow and become woody. D. tenuicaulis and D. apiculata have been introduced into New Zealand and these were available to Melanie. By determining the chromosome number of various accessions, she was able to achieve combinations between the various Tree Dahlia species and more importantly D. coccinea, one of the two species that gave rise to the modern hybrid garden Dahlia. As a result, a whole series of Tree Dahlias were created with a range of flower colours and shapes. ‘Timothy Hammett’ named after my late older son, is in my estimation the very best. It produces truly massive woody stems and flowers throughout much of the year.
I have done my best to maintain this genetic material, but the brutal truth is that plants are safest when in commercial production and Tree Dahlias simply do not fit the current supermarket model of the retail garden trade. Equally we are not a production nursery, we are breeders and one needs to be properly geared up to supply plants by mail order. For this reason, we have decided to offer seed in the hope that enough kindred spirits will help to keep this germplasm alive. To check viability of the seed, which is slender in comparison with that of the garden dahlia, we germinated seed last season and planted out the resultant plants. They were planted fairly late so didn’t reach their full stature, but demonstrated wide variability in plant habit and flower form and colour.
I have again lost ‘Orchid’ that everyone seems to want but there were individuals in the population, which resembled it in both shape and colour, plus others of interesting colour on the red/yellow side of the spectrum. Because of the hybrid nature of the seed from open-pollination and the hybrid nature of the parents, there is little point in offering seed from specific selections; better to offer a mixture.
Plant breeding, however scientific, is a lottery. Every seed will not produce a winner but I am sure there will be gems amongst this seed and between us we can preserve and develop Melanie’s work of two decades ago.
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Although the original, wild Sweet Pea, Lathyrus odoratus, from which all Sweet Peas have been derived was summer flowering, strains have been developed that are able to flower at different times of the year. This is controlled by the length of daylight hours, which varies both by season and geographic location. As a rule of thumb, Summer Flowering strains require 12 hours daylight to initiate flowering, Spring Flowering strains require 11 hours, while Winter Flowering strains require only 10 hours.
Spring Flowering types are best sown in the autumn while Summer Flowering types are best sown from mid winter in areas with mild winters like those experienced in Northern New Zealand. Spring and Summer types produce more sturdy plants, which produce strong basal shoots that soon take over from the primary shoot. Notwithstanding both the Winter and Spring strains perform very well if sown at the same time as the Summer types.
Scent is a difficult characteristic to breed. Expression of scent is very much dependant on temperature and humidity, while different people have differing ability to detect scent. Notwithstanding, Keith's work in combining the colours of the ancestral cultivars with bigger flowers and longer stems has also resulted in strongly perfumed cultivars. His 'High Scent' is recognised as the world benchmark for scent. This has smaller flowers with a clamped keel, but new introduction 'High Society' combines a waved, crisp white ground picotee edged pink flower with strong scent.
Very frequently, home gardeners are advised to soak seed overnight before sowing. This is unnecessary and potentially harmful for any hand harvested seed obtained from this website. Because of harvesting methods, seed from field production can on occasion result in hard seed coats, which delays or prevents germination. This is why the idea that seed needs to be soaked to identify hard seed has arisen.