Dicksonia antarctica

[johnw]

We have no luck whatsoever with ferns in general.  Their cultivation remains a complete mystery to me.  We have a potted tree fern which does not seem to be growing with the abandon we expected, so far this year it has only put out 6-8 fronds which are somewhat shorter than last year's fronds.  Presently it has stalled. I keep the circa one foot trunk watered everytime I pass it by and the soil watered when on the slightly dry side.  It was repotted last summer.  Should I be feeding it at all? Any thoughts welcomed.

I ask as it's at the stage where it is taking up too much space so some gain in height would be appreciated.

john

[rob krejzl]

D. Antarctica is fairly slow growing even when doing well. Generally the trunks re-establish quickly; it's a common sight down here to see cut, stacked trunks starting into growth whilst waiting for sale in a nursery. It may just be that your's has dried out a little at some stage. They are difficult to kill completely though.

They do have a quite large root system once established. I once decided to move an entire 2 metre fern, rather than take a chainsaw to the trunk as is the normal advice. The root ball consisted of a solid mass of rhizoids up to about 60 cms out from which all the soil had been excluded - not really surprising given the sort of lateral force that can be exerted on the crown.

My advice would be  much the same as you already seem to be doing. Consider a move to as large a pot as you think you can cope with. Water into the crown and down the trunk (especially important in spring, when you should see the new rhizoids growing downwards). Keep the pot moist but not water logged. If you do feed try feeding into the crown with something general purpose (I've used handfuls of fertiliser granules without obvious ill-effects). Since they grow beneath the canopy a little shade and humidity are also a good idea. Other than that, a lot of patience.

[Anthony Darby]

Garden centres in Scotland say Dicksonia antarctica grows at a rate of 1" per year. D.squarrosa is more like 10" per year. We have some very big species, up to 30 metres, here in New Zealand.

[Neil J]

I strongly support Rob's advice.
These ferns have a greater need for moisture than for fertilizer. Drying out is more likely the problem. The whole "trunk" is a fibrous root mass and holds a lot of water. Place a hose in the top of the "trunk" & let it trickle until the whole thing is well saturated. Repeat any time things get at all dry. They will grow considerably more quickly if they are kept moist.
Whilst a larger pot would help, the fern will do much better if it is transferred into the ground.
The other consideration could be your water. These traditionally grow in wet acid soils. They also hate being exposed to strong winds.
Prune the old dried fronds off flush each year as the new ones emerge to take over.
These are very beautiful large ferns in the right conditions.
Good luck!

[johnw]

Thanks so much Rob and Neil.   First off this is either a spore-grown or tissue-cultured fern I got from Briggs Nursery in 2008 as a 4" deep pot, so 7-9 years old.  I have been faithfully watering the crown and trunk but wonder if I have been relying a bit too much on that to soak the soil  as well.  I have been warned not to soak the crown in the dead of winter just the soil.  It was repotted annually, last year was the last time, a 2 pot size jump as we couldn't keep it watered.

Next repotting  I will tease away some of the soil and place in 1 pot size up. Wonder what you recommend as a mix?

As our tap water goes very alkaline in summer I switched to rain water this year though had no ill effects in the past.

In this climate we must store the fern undercover, thus it retains last year's fronds which we leave on.

I am a tad wary of putting organic fertilizer (fear of a goopy mess in the crown over the long winter here) or inorganic (fear of summer burn with release).  Do the roots or is it the trunk that absorbs fertilizer?  I have some fine-grained IBDU (Isobutylidenediurea slow release) designed for golf greens and wonder if a tablespooon or half that  on the soil surface would be okay; I think this is now known as Floranid and the recommended rate is 5lb. / 1000sq. ft. and is known as the safest slow realease there is. I also have some dried pelletized leaf and grass clippings.

With thanks

john

[rob krejzl]

First off this is either a spore-grown or tissue-cultured fern

So I don't have to make my ritual complaint about our forestry industry.

As Neil says the trunk is a mass of rhizoids, most of which will already be defunct. The crown sends down fresh rhizoids every year, so watering and feeding from the top at least until you're sure it's in good healthy contact with the soil makes sense. Whether and what you feed, and how you do it I can't really help with except to say that I doubt it's a gross feeder.

As for the potting mix, since it's a rainforest understory plant I'd suggest something with a high organic content. I've seen them growing atop karst limestone, where the topsoil must be entirely organic.

Removing dead fronds to reveal the trunk is a cosmetic procedure. Mature ferns not in "captivity" retain a conical skirt of old fronds.

Now the sun has come out and rain has stopped. Time for me to do likewise. Good luck with it.

[David Lyttle]

Tree ferns are generally unfussy plants. They like a lot of moisture though they can tolerate periodic drought. Different species have slightly different requirements in term of optimum moisture, temp etc - I cant give any specific advice for D. antarctica. Here is a picture of showing two species of Dicksonia growing in southern New Zealand. The one with the prominent skirts is Dicksonia fibrosa,  a favourite of mine. The taller one in the background without a skirt is Dicksonia squarrosa which is a commoner, almost weedy species. They are growing in mixed broadleaf/ podocarp rainforest on old consolidated sand dunes ie a free-draining site but not a highly fertile one. The challenge is to produce those conditions in a pot in Nova Scotia!

[johnw]

Thanks all yet again.  We've had some very heavy rain since my first post and at least three larger than normal fronds have appeared.  I sprinkled about 1/16 tsp of IBDU slow release in the crown and will await the results.  In a normal year this tree fern seems happy with all our fog and dampness but May and June were dry.  Hoping for a major upsize.

john