Yes, I know, the New Year has just begun and it’s already time to sow the first seeds of the new season? It may not seem likely, but yes, if you want dracaena spikes (Cordyline australis, syn. C. indivisa) in time for your summer garden, you’ve got to start them really early.
What garden centers call “dracaena spikes” or just “spikes” are actually young plants of the New Zealand cabbage tree. They form a fountain-like plant with narrow arching leaves that has been used as the center plant (the “thriller”) in containers since Victorian times. But the growth of this plant – in fact a tree in its native land – is painfully slow, so you have to sow it very early in the season.
Soak the seeds in warm water for 24 hours (a thermos is handy for this purpose) and then sow them 1/2 inches (15 mm) deep in light soil. The seeds germinate very slowly – in 4 to 6 weeks – and need quite a bit of warmth: about 77- 80?F (25-27?C).
Personally, however, I no longer sow cabbage trees. Instead I keep my plants from previous years by moving them indoors for the winter. You can even leave them outdoors in mild climates. USDA zone 9 is usually safe, sometimes even zone 8… until you get that one winter with a really hard, lasting frost, then you lose them. Indoors is safest everywhere outside of the Tropics.
Obviously, over time, after 7 or 8 years or so, they become too tall and treelike for use as a container garden plant, losing their lower leaves and revealing a bare trunk you can no longer hide. When that happens, though, I take a cutting or air layer the top of the plant and that gives me a plant of just the right size for container use. Then I cut the remaining bare stem into segments about 3 inches (8 cm) long, which gives me a lot of cuttings I can pot up, plus a new plant will also grow from the stump. And you can even cut the thick roots into segments and they’ll sprout too. (If you do all the above, you’ll have to hold a cutting sale in the spring to get rid of all your new plants!) Again, though, you’ve got to take cuttings early if you want them to form usable plants by spring.
Of course, you could skip starting your own cabbage trees entirely and simply buy plants from a nursery in the spring. After all, they’re available just about everywhere. That’s fine if you have the money for that sort of thing, but I prefer to save my cash for plants I can’t get otherwise and instead keep my “spikes” from one year to the next.