Gunnera manicata (Brazilian Rhubarb) is probably the biggest herbaceous plant on the planet, massive spiny rhubarb leaves up to 2.4 metres across are thrown up every year before dying back to the hairy crown in winter. The flower candles contain many slender green fingers studded with tiny flowers, forming berries containing the seeds. Gunnera are not properly hardy and small ones are especially vulnerable; if you live in a cold area there is always a risk of losing them. Protect the crown with a deep straw mulch in cold winters. It does need plenty of space, at least 4 square metres per plant, and must be planted with the crown above maximum water level. It needs loads of water to support those huge leaves but will die if the crown is submerged.
PLEASE READ EXTENDED DESCRIPTION AND CONDITIONS BELOW.
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IMPORTANT NOTE: RHS Wisley have published their long awaited paper, authored by Julian Shaw, which vindicates what I have been saying for years. It’s many pages of pretty heavy and detailed botanical description, but the gist is that ALL Gunnera sold in the UK and most of Europe for the last hundred years are not G manicata, or G tinctoria, but hybrids of the two now referred to as Gunnera x cryptica. Some look more like one and some like the other, but that is in the nature of hybrids. I have been informally advised by APHA that there will be an unspecified period of grace in which remaining stock can be sold; these same plants that we have always sold, and after they are gone, that large Gunnera will no longer be permitted to be sold. My position remains that since there are hundreds of thousands of these plants all over the UK and Europe, many in historic gardens that have been there for decades, with no evidence of a triffid-like world domination policy, the risk of any significant detrimental environmental impact in domestic gardens is extremely low. If I thought otherwise, I would not sell them. We will be selling our small remaining stock as G x cryptica until they are gone and there will be no refunds relating to nomenclature.