Graham has written (see comments - Lichen, moss and liverwort) and asked about whether it is really necessary to cover the roots of Gunnera manicata with bracken when the foliage dies back in autumn. He also asked for my thoughts as to whether the species tinctoria is a better choice, because it is hardier, having become a pest species in Ireland.
|Gunnera manicata at Fletcher Moss Gardens|
Gunnera manicata is sometimes referred to as the giant Brazilian rhubarb, because it comes from Brazil and has big leaves like rhubarb. However, it isn't edible and can grow to over six feet, ideally next to water. Interestingly, it has developed a relationship with a nitrogen-fixing bacteria in much the same way as members of the pea family, and this makes it easier for it to survive in nutrient poor soils. The closely related G. tinctoria comes from Chile and differs in that the stalks are edible, being used as a vegetable or eaten raw when the stems are peeled.
My experience of growing G.manicata was at Fletcher Moss Gardens, where we religiously covered the roots, in the traditional way, with the old leaves, pegging them down to prevent disturbance. When we had a series of mild winters the thought was that maybe we could get away without carrying this out, but thankfully we persevered because we were then hit with some humdingers which would almost definitely have wiped the plant out. In view of the fact that Graham lives in the hills above Cockermouth - a hardier environment than the South Manchester Riviera - I would say the plants should certainly be protected in this way or, as he suggested, with a thick layer of bracken.
The R.H.S. classify G.tinctoria as being even less hardy than manicata, so I would suggest that it also will need protection. The climate in Achill Island and County Mayo in Ireland, where it is invasive, is probably considerably milder than the badlands of Cockermouth, explaining its rampaging nature there.
Thank you for commenting, Graham - all questions are welcome.