Gunnera Manicata

I'm planning a bog garden and am digging out a sizeable area to two feet deep which I plan to line with polythene round the sides to retain moisture without restricting root growth.I want the main feature to be a Gunnera and wonder what would be the best infill to promote growth.I am intending to mix several sacks of leaf mould to the soil to add acidity and heavily composted.Plus after planting covering the area with bark chippings to slow evaporation.The site gets direct sunlight for half of the day.
Am I going in the right direction to encourage the growth of this 'giant rhubarb'?

 

It needs constant moisture so the leaf mould will certainly be helpful, as will any soil that retains moisture

 

Probably out on a limb here, as I've never had the space to grow a decent gunnera.

But shouldn't a bog garden contain a good heavy loam soil.

I'm thinking masses of leaf mould will just rot down after a year or two and tend to disappear, might even stink a bit while its doing it.

 

Sorry Pete, but I don't understand that thinking ???
Leaf mould, rot down and disappear??? stink???
I have been producing super leaf mould for donkeys years. None of those things have ever happened to the stuff I produce
Leaf mould should only be used in the second year of production. It is terrific stuff.
Here is my gunnera this year, having survived a most dreadful winter without protection

 

Beautiful poolside display.
That's a magnificent recovery. Obviously the snow would have made the usual die-back a lot worse, but do you have to clear out a lot of dead foliage in most years? Does a gunnera take a lot of management - over crowding/ feeding etc?

 

Raebhoop, you do realise how big G.manicata gets? 10ft by 12ft ( 3m x 3.5m ).

 

OK just my assumption from adding organic matter to raised beds, it disappears and the bed sinks.
Also that decomposing organic matter in bog conditions might start to whiff in warm weather.

I'm just thinking that leafmould might be OK as a top dressing but not as one of the main constituents of the bog soil.

I did not mean to cast a slur on your super leafmould.

If I'm wrong,.......... I'm wrong:D

 

Hopefully !
If the leafmould is contentious should I just rely on the existing soil with extra compost? It's just that I've read the Gunneras like acidity in the soil.The area has been a weed bed for many years and the soil is just common or garden muck...no clay...excuse my technical terms I'm no Titchmarsh.

Nice plant Whis4ey...but I take it I shouldn't follow your example and protect a younger plant from the frost?

 

Sorry, interupting the flow here. Raebhoop......is that a ringneck parrakeet on your avatar? Looks like a tame bird.

 

One of my hobbies...:D

 

The only comment I am going to make about leaf mould is, it is a woodland product and not a boggy area material. Bog gardens are clayey and peaty situations.

 

Up until last year I always protected the gunnera with its own leaves every year. Last year I wasn't told in advance just how cold it was going to be, and as I was otherwise busy, I did nothing. The thing has still survived, although I think it just might be a little weaker.....
The only time it suffers is when we have a spell without rain, and the ground gets a little drier....
Pete ... I always add leaf mould to my composts and top dressings. Any organic matter helps make for great soil after a few years. I dig some in to almost every planting hole. In the second year you could actually lift it and eat it, as a famous bearded scientific horticulturalist used to say
I find it is great for holding moisture
Mind you, I don't recommend trying to eat it ....

 

Just to go back a bit here, Gunnera doesn't actually need an acid soil at all. It needs a permanently moist humus rich soil. As Dai says, leaf mould is a woodland product, but you could use it along with well rotted garden compost to add humus.
If you are making your bog garden somewhere that's naturally already wet, you just need to add lots of humous. But if you are making a bog garden from a free draining non boggy bit, you would need either a clay layer at the bottom, or maybe a plastic pond liner over the whole area. You could puncture this in a few places so it drains slowly. I know we are not supposed to be using too much peat...but it is really good for holding moisture and you could mix it with some of the soil you dig out. (If you do use peat - it will then be ideal for acid loving plants too.)
Cover the crowns through the winter to give some frost protection too.

 

The area I have available for the bog garden is not naturally boggy.I already planned to use poly liner for sides and maybe parts of the base .But if I line the whole area with just a few 'weep' holes what will be the effect on root growth as the plant ages? Unless I go much deeper.

 

The roots aren't actually very deep. And, anyway, it can become quite a massive plant, so you will want to curb its growth as much as you can
My own plant reached over 18 feet high last year for example, and it spreads too
Are you quite sure you have enough ground?