Under optimum conditions (all-year growth without defoliation) Cyathea cooperi can increase trunk height by up to two feet a year. They are as fast developing as any tree fern you're likely to encounter - in contrast to Dicksonia antarctica - although Cyathea medullaris can also be very quick growing. In the UK, where I grow many tree fern species, that kind of growth rate is only possible under glass. But even outdoors in marginal California you should be able to achieve about half that rate of trunk development - more if you feed very regularly during your summer watering regime. They like LOADS of water in the hot months, and - by tree fern standards - are fairly gross feeders. High nitrogen is what they require - so stay clear of tomato feed, which is rich in precisely the wrong nutrients. Any general purpose fertiliser, well diluted, will be suitable during the peak growing season. But then lay off completely during the winter close-down. You're fortunate to be able to keep sub-tropical Cyatheas alive through the kind of winter minimums you describe (none of my sub-tropical species would tolerate 'sub-zero' temperatures of that severity). Our wet and mild winters in the UK are statistically warmer than your Californian absolute minimums, yet most gardeners here would still be unable to have Cyathea cooperi outside if there was a risk of frost. But then our two climates (both notionally USDA Zone 9 or 10) have very different implications for what we can, and can't, grow. Cyathea cooperi are still very uncommon indeed on the British fern scene.

No basis whatsoever. Tree ferns don't come in male and female genders, just GENERA for the overall families (like Dicksonia, Cyathea and your Cibotium); and SPECIES which describe the individual types within a family (eg, Dicksonia antarctica, Cyathea cooperi, Cibotium glaucum, Cibotium chamissoi, etc). Some fern genera contain literally hundreds of different species within the family, others maybe one or two. Some genera have died out completely and all the species are regarded as extinct. Others are clinging on for dear life or are close to becoming endangered. The Cibotium family genus is kind of doing okay for now, although the general medium-term trend for all tropical rain forest and cloud forest habitats is grave indeed. Hawaii has four accepted tree fern species: Cibotium glaucum, C.chamissoi, C.menziesii and C.nealiae. There is one other hybrid Cibotium variant that occurs naturally, but it's arguable whether this should count as a true 'fifth species' as it may not be able to reproduce and is instead simply the result of a one-generational cross between two of the other accredited species. Theoretically it can occur with every sporing by the contributing parent plants, it's just that the resulting hybrid offspring might not be truly reproductively viable itself, which is the standard criterion for assigning species status to new mutant strains. Like donkeys/asses and mules, I suppose. Even so, botanists are always revising the naming system and new species are regularly created from out of the ranks of previously unclassified plants. Maybe your inter-bred 'fifth' Hawaiian Cibotium will one day recieve the official stamp of 'new species'. Unfortunately, all those Hawaiian names for Cibotium tree ferns - Hapu, Hapu'u, Man Fern, etc - are misleading, misapplied, and really only have a validity as folklore and perhaps when researching ethnobotany and the uses to which plants were put by ancient cultures. There's nothing about Cibotium in the general literature or on the internet that isn't pretty flaky, I'm afraid! Be very suspicious of anything you read about tree ferns in Hawaii, especially in the tourist press or gardening media. As for making sense of the diversity of flora and fauna around us, and transfering that knowledge across to conservation, gardening and serious horticulture, it's more reliable to use a rational and internationally understood naming system. It's impossible to look up stuff about plants, or talk about them accurately even within your own locality (let alone across the internet), unless the botanic names are applied. Forget that it originally comes from dead Latin and 19th century planthunters' names that we've all forgotten, and just see it as a reliable plant label that means the same thing anywhere on the planet, to expert or lay-person alike. So, no male or female Cibotium tree ferns. Just different species, plus continuously mutating sub-species, local variants and hybrids. And lots of arguments by committees at international botanic conferences... Steve - Brighton, Sussex Coast, UK

Hello, allow me to add a couple of points for those tree ferns that I so envy growing in your part of the world. Cyathea cooperi and brownii are a group of Cyatheas that require exposure to sun when they grow older. These belong to the Sphaeropteris group that is generally made up of fast and large growing tree ferns. When young, they need filtered shade. AND they need good drainage and constant moisture. 39C in the day? does the night temp drop to 20C or lower? If so, the Cyathea cooperi or brownii might be able to take a spot with sun. (Best is morning sun and afternoon shade) The other tree fern Cyathea australis on the other hand is a strictly forest shade creature.

Very excited, just bought a Dicksonia antarctica too! I asked at the nursery if they had any in stock. The main owner wasn't in and so I described what they looked like to the assistant and she responded with a little excitement too as she guided me towards their 'private' poly tunnel where they keep plants that aren't at their 'showy best'. I was trying not to show too much glee at seeing the very wide stump in the large pot in front of me and so commented negatively on the few tatty fronds that remained on the plant. The assistant rang the owner and he asked for 30 pounds. I genuinely only had 20 pounds in my wallet as I wasn't intending to buy anything until I had fixed the garden first. They accepted and I brought my new baby home! I hadn't given it too much of an examination in the nursery aside from checking for new growth (of which there were new fronds just about to make a break for daylight), but as soon as I got it home I realised why the plant looked so wide... It was two!!! The larger trunk is around a foot tall and the smaller trunk is around 8 inches. BARGAIN ALERT!! The largest remaining frond is easily 30-36" long. A good watering of the crown washed away some of the brown fur and fully revealed very prominent new growth. Upon my discovery I did wonder if to separate the two plants but I have now just about decided to keep them together to form a more bushy tree. When I am ready to plant them in the garden I may take a look at the roots to see just how entwined they are and let that be the decider. Any comments on this? As you may be able to see from the photos, the area where they are going to be planted does look quite flooded after heavy rain. This soil has not been forked for many years and it is hoped that doing so (and raising the earth to a slight mound will help drainage sufficiently. Is there anything else I can do to assist drainage or do you think the ferns will be okay? Here is a link that might be useful: Pics of my tree fern(s)!