Tuesday, 28 October 2008

End of the growing season arrives

At Claines Canna we have been visited by our first frosts, much earlier than normal, and the foliage has now been chopped down and lies covering and protecting the underground rhizome from any hard frosts.

The worst frosts that freeze the ground and destroy canna rhizomes in the ground do not normally arrive until January, traditionally the hardest weather month of the year, however, with the extreme weather changes that we are now experiencing we are taking no chances!

Normally the foliage would have gone straight away to composting in the 1 ton sacks you can see in the background, but this year they will provide frost protection while we lift the rhizomes.
Now begins the hard slog of lifting all the Cannas in the collection, splitting the stock plant rhizomes, planting about a third of each plant in the soil inside one of our polytunnels, there to over-winter for the next 6 months. The remainder of each clump will end-up either in the land-fill if not considered virus-free, or packed for despatch if it is considered to be a clean specimen.

The stock-plants have to now spend 6 months underground in the poly tunnels. That is half of their life. We are determined to spend more time this winter getting to understand how to over-winter optimally, rather than walking away for a rest from growing them over the summer. We will report next spring on our observations.


  1. Malcom, with the cannas you overwinter in the ground, inside a polytunnel, would it not pay dividends to apply a dark coloured mulch over them?

    I know that research conducted here in Australia at Burnley Horticultural College showed that normal garden mulches like pea straw or similar products actually kept the soil colder over the winter than beds without any mulch at all. Apparently the pale coloured mulches prevent daylight warming the soil. Without a mulch, the soil warmed perceptibly during daylight hours and gave off the warmth it had stored when the night was cold, thus ameliorating the depth to which a frost penetrated. Mulched beds did not warm up during the daytime and so did not radiate stored heat and the frosts penetrated much deeper into the soil.

    It seems logical that a dark coloured mulch would absorb more heat that a greyish aged straw one. Granted, out frosts are nowhere near as bad as your freezes, but it still might be worth trialing various mulches as opposed to no mulching at all.

    What about using bubble wrap as a mulch? Just unroll it and cover the beds during your riskiest times. You could have it at the end of each bed on something like a giant hose tidy with handle attached for reeling it in. Cheap, and you can buy commercial rolls of bubble wrap in wide widths. Heat would penetrate and the bubbles would insulate during the nights.

    Have you thought about spraying your mulches with a dark dye to fascilitate absorbing warmth during the day?

  2. Helo Malcolm,

    Le gèle est arrivé en Belgique.
    Cette nuit: 0°C
    T° au sol: -2°C


  3. Hi Dale,

    That's a great starting point. I'll look into mulching as a starter. We also have horticultural fleece available, but that is white and I like your ideas about absorbing heat. Even during the coldest days the polytunnel does heat up during the day.

    On the opposite side, when the ground heats up the Cannas start sprouting new stems. A vicious frost would just destroy a sprout.

    I tried black sealed bins full of water last winter, and they did retain heat during the day and gave it out overnight. However, they took up so much room that I wheeled them outside and emptied them after a few months of struggling to walk around them.

  4. Bonjour Raphaël,

    Ainsi, c'est la fin de votre saison aussi bien? C'est maintenant l'heure de penser à l'année prochaine et est-ce qu'une partie échange aussi bien?