Harry Harrington demonstrates the black bag method for rescuing sick or newly collected bonsai trees. Wrap the trunk in a moisture-retaining black bag, mist continuously, and cut a small hole at the top for light to encourage upward growth. New shoots don't guarantee roots have developed, so remove the bag only when the tree is truly stable, or it may collapse in hot summer heat.
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Hi, today I thought I'd take you through the black bag technique. It's a fantastic technique for reviving sick trees and also recovering newly collected trees, and it's something that I and many other people have been using for many years now. Essentially, the black bag is used to surround your newly collected tree. It goes over the top of the new trunk and it creates a very, very humid environment, particularly as you keep spraying water and misting the trunk. And as the temperatures warm through, you create this very, very humid environment. Now I have all my collected trees in a polytunnel as well, which adds to that. Put the black bag technique can be used anywhere in your garden. Now I tend to collect hawthorn and blackthorn, and the, the bagging up and that extreme humidity that this, this technique creates is essential for getting your hawthorn and your blackthorn to recover well. They absolutely love the humidity. Don't worry about the temperatures that You may get in your polytunnel or inside the bag. They can hit 30 or even 40 degrees centigrade. It's that humidity that is absolutely essential. Another very useful part of this concept of using the black bag is. Tearing a hole in the top of your bag and allowing some light to come in through the very, very top. This is a little like forcing rhubarb, if anyone's grown root vegetables or fruit in their garden. By having light at the very top of the trunk but the rest of the trunk in darkness, you encourage the tree to grow from the top of the trunk and not just bought the trunk itself and grown new suckers. And it's something that can happen with a number of species such as pyracantha, again hawthorn, blackthorn, and birch. So that appearance of light at the top almost imitates the trunk being under the ground and suckering from the very top of the trunk. I've been asked a number of times at At what point you remove the bag itself. Now, with many deciduous trees, after they've collected, they will bud out and create quite long shoots simply off the energy, stored energy in the trunk. Having new growth does not mean that the tree itself is rooted, and what can happen is you can get to midsummer when temperatures get very high, in the 30s or 40 degrees, and dry. And the tree will just collapse, and that's because it's not actually produced any new roots. To help promote root growth, Rhizotonic is well worth using and genuinely encourages rooting in all plants. Spray the leaves and the soil once or twice a week to encourage stronger rooting in your weak or newly collected trees. Keep misting the inside of the bag to keep the trunk damp at all times, but try to keep the actual soil on the dry side— damp but not soaking wet. These trees are now in their second spring after collection and so aren't bagged up. Some trees, particularly Hawthorn, may not come into leaf until well into the summer. I've had some trees not leaf out until as late as July and August. Don't give up on a newly collected tree unless you are certain it is dead. It's never too late to start bagging your tree up, even after the first leaves have opened in spring. Newly collected or weak trees will still benefit from the humidity that a bag provides.
