Pleast note: Some folks experience skin irritation when handling Strelitzia seed. Wearing protective gloves will eliminate this possibility.
Do not chip or mark the seed coat. When ready to plant, merely remove the orange tuft (aril) and soak the seeds overnight. Sow seeds in moist potting sand (not beach type) or a well-draining soil mix. Mixes with inert materials such as perlite or vermiculite promote good drainage. Good commercial potting or seed-starting mixes can usually be found at most home improvement stores or gardening centers. Add a slight dash of ground cinnamon to the medium and stir it in well . . . Cinnamon is a natural anti-fungal agent and will help prevent "damp off", the great killer of germinating seeds.
Push seeds into the medium to a depth of about 1 to 1½ times the length of the seed. I.e., if a seed is ¼ in. (8 cm) at its longest measure, then sow it ¼ in. to 3/8 in. (8 - 12 cm) deep.
Covering with plastic will help keep the medium moist. One easy way to do this is to cut the bottom half off a plastic beverage bottle and easing the cut edge into the medium so as to cover but not disturb the sown seed. Discard any bottle cap - - an opening is needed to provide some transport of air. Another method is to cut a small hole in a plastic baggie and tent the container with the bag, taping the bag's edges to the side of the container. The hole in the baggie is also for air transport.
For optimum germination results, place the container with the sown seed in an area where the temperature is 75°-80°F (24°-27° C). Lower temperatures will lengthen the time needed to germinate. Make sure the growing medium is kept moist, but not soggy. Strelitzia seeds do not need light to germinate, so these seeds can be germinated in the space where your hot water heater is located.
Germination can begin within 30 days but the norm is more like 60 - 90 days. Once begun, Strelitzia germination can be erratic, carrying on for 6 months up to an entire year. You can begin to inspect your container after a week or so, then continue to check weekly making sure the growing medium contains enough moisture - but is not soggy. Light misting is recommended when you feel the medium is getting dry.
As soon as any bulges, roots or shoots are observed, remove the germinated seed and pot it up in a compost of half peat and half building sand (not play sand or beach sand). Perlite can be used in place of sand. Again, add a slight dash of ground cinnamon to the medium and stir it in well. Place the seedling container where there is plenty of light and air.
Strelitzia sometimes produce a root without a leaf shoot. Also, young shoots and roots are susceptible to fungal attack. The addition of ground cinnamon to the second medium should help deter fungal action, but getting your potted up Strelitzia into light and fresh air as soon as possible is also important.
Young plants are best grown in semi-shade as the leaves tend to burn in direct sunlight. Regular re-potting into successively larger containers will allow the young plant to develop rapidly. If root development is restricted, it can retard growth of the plant.