The Black Tree Fern ( Cyathea medullaris ) is a large tree fern that is native to New Zealand. It is recognisable by its thick deep black frond stipes, reddish coloured hairs along its stipes and the circular-hexagon shaped scars on its trunk from old fronds. It is a beautiful species that is quite hardy to cool temperatures, wind and sun, often seen growing in the open in its native range. Due to its large size it is not a common backyard specimen, although very ornamental.
Cyathea medullaris is fast growing once established and also known as New Zealand Black Tree Fern or Mamaku.
Growth
The slender trunk of the Black Tree Fern can grow to heights of 20 metres tall, with a diameter of 30 cm’s. Its bright green fronds can grow to a length of 4 metres long and the stipe (frond branch) although starting off green, matures to black .
Cyathea medullaris is often seen growing above other trees or out in the open in sunny positions, so is hardy to sunshine. This said, it will only tolerate these conditions if the soil around the base is kept moist; it is not drought tolerant. It is hardy down to approximately -3°C and will cope with some winds but grows best when protected from both.
FAMILY:
Cyatheaceae
CLIMATE:
Temperate to Tropical
TEMPERATURE RANGE:
-3 to 32°C / 25 to 90°F
SOIL TYPE:
Humus rich, moist soil
LOCATION:
Full Shade – Full Sun
HEIGHT:
Up to 20 metres (65 feet)
WIDTH:
Up to 8 metres (26 feet)
pH:
5.5-7.0
GROWTH TYPE:
Evergreen, Fast Growing.
WATER REQUIREMENTS:
Medium.
POLLINATION:
Spores form on the underside of the fronds, which have both male and female organisms present.
MATURITY:
2-5 years
GERMINATION RATES:
68-88%
GERMINATION TIME:
Germination process will usually begin around 2-6 weeks, however it may be many months before they start to look like little ferns.
SEEDS PER GRAM:
Too many to count – well into the hundreds of thousands.
MEDICINAL QUALITIES:
No
WEED POTENTIAL:
No
FACTS ABOUT CYATHEA MEDULLARIS (NZ Black Fern)
Although it is somewhat cold tolerant, the young fronds are not frost tolerant and may freeze and die away in frosty conditions, however will generally grow back once the weather improves in Spring.
The Native New Zealand Maori’s call this fern Katata, Pitau or Korau.
This species has another synonym that is a little more of a mouthful; Sphaeropteris medullaris.
Germination Instructions
HOW TO GROW CYATHEA MEDULLARIS (NZ Black Fern)
Step 1
We cant recommend highly enough how important it is to use a sterile medium for ferns!
Preferably use a new pot/tray or if you are using a container that has been used prior, scrub it with a 10% bleach solution to kill any pathogens.
You can sterilise your soil (medium) by heating it to 60°C/150°F. This can be achieved by putting your pre-moistened medium into a microwave or oven in a suitable container and checking with a meat thermometer that the above temperature has been reached all the way to the middle.
Step 2
Leave your medium to cool in the oven or microwave to avoid any contaminants entering your sterile medium or cover with some tin foil. This can take a couple of hours
Pour your medium into your new or cleaned pot/tray. We personally use clear containers – a Chinese takeaway container or a container base inside a zip lock bag is fine! If the medium is not moist enough, use a spray bottle of cooled boiled water to moisten.
Step 3
Once the soil is cooled, sprinkle the spores sparsely over your medium. Try not to sow them too thickly as they may overcrowd each other (but this is not easy)!
Place your lid over the top and seal (or place inside ziplock bag and seal) to retain the humidity and moisture needed to promote germination.
Place on a shaded but light area, not in direct sunlight.
Ideal germination temperature is 17-22°C/65-75°F, initial signs of germination take 2-6 weeks.
Step 4
At first you will notice a moss type green film growing over the surface of the medium, following this you will see your little ferns beginning to develop, this can take a few months! Continue maintaining the moist, humid environment inside the container or zip lock bag until the sporophytes (young ferns) are 2-3 cm’s tall. At this stage they can be re-potted, however can survive happily in the above environment for 12 months if they have the room!
When transplanting, keep in similar conditions with each fern in its own zip lock bag for two weeks before opening the bag intermittently and allowing the sporophytes to slowly acclimatise to the outside environment over a week or two.
Acclimatizing can be achieved while they are still in their original environment if there is still room (they are not squished)
Final position should be in dappled shade to part-full sun. Keep protected from cold wind and frost.
If no young ferns are evident after 12 weeks, try watering with a diluted liquid fertiser (1/4 the normal plant dose) often this may encourage sperm release and fertilisation.
