Growing Map - USA & Canada

Where can I grow delphiniums in the USA and Canada?

The above map is has been compiled using information from a number of Growing Zone Maps and from growers of our New Millennium Delphiniums in the USA and Canada. It is meant to be a general guide only and local conditions and experience should always be taken into account.

growmap usa

Generally speaking the limiting factor for growing our delphiniums as perennials in the USA and Canada is summer heat. Ideally they should not be subjected to temperatures in excess of 80degF for long periods. However, we have found both from our own experience of growing in hot houses and from the experience of gardeners in the USA and Canada, that our New Millennium Delphiniums will perform well where temperatures reach 86degF for an average of no more than 45 days during the summer. These general areas are coloured green on the map. Best results are obtained where care has been taken to provide shade, or dappled shade from the hottest summer sun and if this is done our delphiniums should be truly perennial, lasting several years.

In areas coloured terracotta New Millennium Delphiniums may be grown as an annual, or at best a short lived perennial. In these areas the plants must definitely receive afternoon summer shade and efforts be made to keep the roots cool (straw mulch etc). Nonetheless, good management can still be rewarded with fine blooms. See growing information.

Avoid growing our delphiniums in the yellow areas unless you have an air-conditioned conservatory, where they will thrive.
 

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Dowdeswell's Delphiniums - Wanganui, New Zealand