Dahlia Excelsa

This is the toughest of the tree dahlias species. D. excelsa 'Double White' has white anemone flowers from July to September and is a strong garden statement.

Expect 2m growth on first year, then cut down to the ground for vigour and even more flowers in the following seasons. Expect 4m growth second year. Tubers grow to 2-4m, are elongated and thin. Anemone flowers are plentiful and occur at the top of stems so a ladder is required to pick them. Best [picked in bunches.

D. excelsa 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.

Stems can grow 80mm thick and are mostly hollow but very ligneous. D. excelsa stems are robust and can tolerate 50kmph winds.

Canes are soft cream brown with lime green leaves. Stems turn pale grey to brown after average six months and become more ligneous (woody), and heavy towards spring. Flowering from May to September each year with at least two flushes.

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 chainsaw 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. A crowbar is useful to divide old tuber clumps. For very old tuber clumps a digger may be required.

You are buying a 30x30cm tuber clump. See picture below.