He and his wife, Janice, are making a living now, but he said their income would more than double if the dollar was back where it was when they bought the 6ha property in 1999 - 43 cents against the US dollar.
The couple moved to Wanganui from Tuakau, near Pukekohe, where they were growing chrysanthemums as cut flowers. Mr Dowdeswell became allergic to chrysanthemum sap and they looked for another flower to grow. They also diverted from growing cut flowers to plants and seeds because it was more worthwhile.
The seeds now make up 95 per cent of their business. The 5000 small delphinium plants couriered out to mail-order customers each spring are a sideline, to keep valuable staff employed and maintain cashflow.
Delphiniums are an alpine plant and Brunswick's westerlies are ideal for keeping them cool.
The trial garden makes use of the elite Brunswick loam, which drains well but also holds a good amount of moisture.
When they started growing delphiniums the Dowdeswells searched out the sturdiest and strongest plant material available. However, its colours were unreliable, which had stopped it being a commercial proposition. But the couple were onto a winner.
"It was very, very early on that we got something nobody else had, nobody anywhere," Mr Dowdeswell said.
He set about improving the plants through breeding. His sensitivity to chrysanthemums has now advanced to include monocultures, and he leaves much of the hands-on work with delphiniums to his manager-in-training, Joe Tweed. He said the fickle flower market was continually looking for new things.
He's happy to oblige.
Some of his latest lines are about knee high, small enough to grow in pots and "aimed unashamedly at the Europe, United States and Russia market, so that people can put them on their apartment balconies in Siberia or New York City."
His is a boutique market. He aims for quality rather than price, and has convinced buyers of his reliability.
Mrs Dowdeswell is the main marketer, working a lot on the internet. They haven't named their latest low-growing delphiniums yet, and the name will be an important marketing decision.
Staff are now sending out plants to mail-order customers and preparing outdoor beds to grow new varieties in the ground. In autumn they will be harvesting, drying and packaging seed.
Dowdeswell Delphiniums' will welcome the public to their big Wanganui weekend on December 1 and 2, when the plants will be in full flower.