Dahlia Imperalis (Cultivated)

The most well known Tree dahla, D. Imperalis (cultivated) has hanging campanulate (bell shaped) flowers that flare at the base.

Flowers from May-June each year here in Auckland.

Most D. Imperalis (cultivated) have white flowers with a mauve center. There is some variation, with some hybrids having pure white flowers, others trend towards mauve and amethyst. You are buying a D. Imperalis that is white with a mauve center. 

D. Imperalis is frost tender. Mulch with course bark 10cm thick. Plant in a sheltered area with free draining soil.

Expect 3m growth on first year, then cut down to the ground for vigour and even more flowers in the following seasons. Expect 4-5m growth second year. Tubers grow to 2m long, are thini and elongated for the first 30-40cm and then bulbous for 30-40cm than thin again.

D. Imperalis are sold bare rooted as a large 30cm clump with multiple stems, tubers and plenty of roots and some soil. These clumps can be shipped.

Plant in soil with excellent drainage on a 30cm mound. Mulch 8-10cm. Water deeply every two weeks in summer if there is no rain. 95% of the matter of D. excelsa is water. This species benefits from regular watering and plenty of organic matter and humus in the soil over summer. Excessive nitrogen during the first three months of growth can cause root burn and produce thin weak stems. Fertilize with a seaweed solution or a balanced fertiliser once a month from Nov to April. Sulphur of potash slow release fertiliser should be applied in February to strengthen stems and increase the number and solidity of blooms later in the season.

With all tree dahlias it is best to cut stems to the ground in October when flowering has finished. A sharp pruning saw is ideal. This is an opportunity to inspect the general health of the tuber formation. Check for rot in central tubers and constricted stem growth.  After three seasons it is best to divide the tuber clump. Tubers can be 4.5m long but don’t be afraid to cut them with a sharp spade to manageable size. The crown region with the eyes is most important to preserve for future propagation. 

You are buying a min 30x30cm tuber clump that is at minimum one year old.