In Praise of RCB's

Your Editor takes up his pen to tell you of an exciting development in the cultivation of palms.
Martin Gibbons, c/o The Palm Centre
mail@palmsociety.org

Pictures: RCB's in three views: Waggies palnted in RCB's in and out of the ground.

No, not IBM's, CFC's or even GMO's! RCB's are Root Control Bags and they are, quite simply, remarkable. Made of a special fabric not unlike that green Scotchbrite washing up pad, manufactured by Du Pont of America, they are available in different sizes and could revolutionize this business of growing palms that we are all in, either on an amateur or professional level, and are especially useful when palms are to be planted out but may need to be moved a few years down the line.

The bags consist of a tube of the special fabric, perhaps 10" or 20" in diameter and a similar depth, which forms the 'pot', with a thick but flexible plastic base. The palm is planted in this bag as though it were an ordinary pot, backfilled with soil, and then the whole thing is planted into the ground. With larger specimens it may be found easier to put the bag into a predug hole, and then plant the palm in it. This is when the magic begins. When the roots grow out and attempt to penetrate the side walls they find they cannot. They come up against the special fabric but while the roots themselves cannot penetrate, the fine root hairs (which of course do all the work) can, and they pass through and spread out into the surrounding soil.

The roots, finding they cannot penetrate, are unable to grow further, and this actually encourages the development of new roots from the base of the palm, which in turn get to the fabric wall, and so on.

The root hairs grow through unimpeded and continue to do the work of seeking out moisture and nutrients as normal, but with the exception of these fine root hairs, the entire root system is contained within the bag. Thus when it is time to move the plant, NO roots have to be cut through, and the entire plant and bag can be eased from the ground just by inserting a spade beneath it and lifting. It's remarkable! Especially so, when you consider that when a palm is normally dug up for transplanting after a few years, ALL the major roots are severed and as much as 80% are left in the ground. The only way to partially avoid that is to dig out such a huge rootball that it's almost impossible to lift. With the RCB, NO roots are severed: the rootball is contained within the bag, which even on a palm of several years old, may only be 18" in diameter!

The advantages are many and various: you have all the benefits of the plant being in a pot (small root ball, convenience, no roots to be cut, transplantable as often as you like, no setback whatever) together with all the advantages of inground growing (unlimited access to nutrients and water, no drying out because of drought, and consequently much faster growth than in a pot).

Here at the Palm Centre we've been using RCB's on a limited scale to grow Trachycarpus wagnerianus One hundred palms were planted in the ground, in these bags, about 6 years ago. The Waggies are now about a metre tall, really nice and compact and in perfect condition. I have to say we haven't looked after them particularly well in terms of watering and feeding them, but even so, being Waggies, they've grown brilliantly and are now wonderful plants, ready to go into their permanent position in the garden. Instead of us now having to hack through the roots to uplift them, and leave most of the severed roots in the ground in the process, a simple levering up with a spade is all that's required and as the accompanying photographs show, they leave the ground with perfect root balls, and will incur no setback whatsoever. The bag can now be peeled off, and the plant can either be potted up into a conventional pot, or they can be planted straight into the ground. Of course, should the new owner plan to move home in a few years, the palm can just as easily be transferred into a new root control bag, correspondingly bigger, and planted in the ground again, for later removal as and when required.

One final thought: when these 100 Waggies were being planted out, we ran out of bags and a few of them were planted conventionally. Six years on, it is impossible to tell the difference between those planted straight into the ground and those planted in bags - until they come to be moved!