Overwintering Gunnera

Gunnera manicata or Giant Rhubarb is one of largest herbaceous perennials grown in coastal BC, reaching average sizes of 8′ high by 12′ wide at maturity. It is a Brazilian native and as such is only zone 8 hardy. However, it can be  successfully grown in zones 6 to 7 with proper winter care. I have used this method of insulation for the past 12 years without incident. That said, younger plants usually don’t have enough foliage to provide proper coverage using this method and will need extra insulation of covered bedding straw or dry leaves until they get large enough.

Tools and Timing – I use an old (and slightly dull) folding pruning saw (making sure the blade is securely locked in place) as the stems are quite succulent and easy to cut through with a slight swing – a machete would be equally efficient. I don’t personally use gloves when cutting Gunnera but many gardeners may them more comfortable to work with as the stems are quite spiny. You want to wait until the frosts begin to appear and minor damage occurs on the foliage (usually mid to late October here in coastal BC). Insulating too early or during warmer temperatures will only cause the crown to sweat and the insulating leaves to rot early due to composting. This can lead to premature exposure to freezing weather and permanent damage or outright plant loss.

Step 1 – Cut all the leaves off at the top of the stem and set them aside in a pile.

Step 2 – Cut the remainder of the stems down to 6-8″ long stubs and stack them  for later use. You can also cut the flower / seed stalks and lay them around the crown for extra insulation.

Step 3 – Cover the entire fleshy crown with a layer of leaves , pushing them down onto the protruding stem stubs to hold them in place.

Step 4 – Use the remainder of the leaves and lay them evenly over the entire crown in multiple layers – these should protrude about 18″ from the crown on all sides.

Step 5 – Take the cut stalks and stack these on top of the leaves to hold them in place. They can also be leaned onto the sides to keep strong autumn winds from blowing the leaves away before they have settled into place.