Pot-bound plants and how to deal with them

A couple of people asked me at a workshop this week, how to ‘open up’ the roots of a pot-bound plant and it became clear, on talking to them, that they were frightened that they might harm their plants if they were too aggressive with them. One said that they’d been told to ‘tease’ the roots out which sounded gentle. I agree, it does. But that’s not what it takes.

The truth is, a pot-bound or root-bound plant is unlikely to thrive. Once the roots get into that behaviour of circling themselves in an impenetrable whirl, water and nutrients can’t get in and the plant can’t grow, even though water, nutrients and growing room are right there – you have to alter the behaviour of the roots so it’s like open heart surgery. The patient will die if you don’t, so you might as well get in there and get it done.

There are two ways to tackle the issue: teasing – which works for smaller plants like this one and less tightly wrapped roots in general, or cutting, which is necessary for bigger plants or where the central roots (the thick knobbly ones) are also circled around each other.

I ‘tease’ with a sturdy three-pronged plastic fork and it’s a brutal process of sticking the fork in, about halfway up the root pack, and twisting it too and fro as I pull down – a bit like getting a really tough tangle out of long hair. As you can see, it’s opened up the rootball on this little honeyberry very nicely. (Please ignore the couch grass, it needs to be dug out but I haven't got round to it yet!) Then, when I plant them I spread the roots out in the planting hole.

Cutting is necessary where the plants are in 1.5 litre or above sized pots. A rootbound plant at that size is unlikely to make good growth even with teasing, so I lay the plant down on its side and with an old carving knife I cut into the bottom third of the root ball, slicing it in half vertically. Then I turn the plant through ninety degrees and cut again so that the plant ends up with four stubby ‘legs’ made of compacted roots. I reach into the heart of the plant by splaying the legs and tease out the larger central roots with my plastic fork before planting, ensuring that the four legs are spread out so the central root system is touching the compost beneath it.

If I am planting in summer, I put any plant that has root-binding into a bucket of water for several hours, agitating the plant every so often so that the roots float free. But for winter plants this can be deadly as it means that the inactive roots are coated in water which can then freeze, constricting and expanding so that the roots, already fairly feeble, are damaged even further by the action of icing and defrosting and may then rot below ground. So for winter plants a really good shake to give the roots a sense of freedom is about all that I recommend. I also mulch over the top of rootbound plants with great care, to protect the plants from frost damage striking down through the opened up soil.

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Posted by The Allotment Blogger on Tuesday, January 3, 2012

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