Stu BurnsPutting down roots

I bought some plants by mail order the other day and they arrived, carefully wrapped, and each sitting in their own individual grow bag, and seem to have survived the journey okay. I have no idea where I will plant them, these babies are Bunya “pines” or Araucaria bidwillii, that will grow gigantic cones sometimes over 10 KG in size, and reach a height of possibly up to 45 metres. I say possibly because there are a lot of things that can go wrong when transplanting trees that can make the tree fail, a nice way of saying die, before they get very large.

Five little bunyas sitting in a row

Five little bunyas sitting in a row

The tree planting instructions enclosed with the plants made me almost jump up and down with frustration, because they were completely wrong. The pamphlet advised that tree roots are very fragile, and shouldn’t be disturbed when transplanting, or the poor little tree would go into shock.

WRONG WRONG WRONG WRONG WRONG!!!!

Tree roots are not fragile, and the best way to ensure a tree does not grow to its full potential is to plant it without disturbing the roots. Why? Because you WANT the roots to get stressed, that way they will put on new growth. Grown in nursery conditions, plant roots have a lush environment, plenty of water, a perfectly designed growing medium that hold enough nutrients and water but drains freely enough to allow oxygen to the roots. And they are bolstered with added fertiliser to give them a good start. But think about what the soil in a garden is like. If you were a plant root would you want to leave your cushy environment and go out into the harsh, cold world?

Garden soils are rarely designed the way potting mix is, and usually need additional nutrients added. Plant roots grown in a pot will also tend to hit the side of the pot and begin circling. If this is not corrected at planting, the tree will probably die, or fall over as the roots never break out of the pot size or shape, greatly restricting the weight the tree can support. Trees that move in the ground months after planting can indicate a poorly developed root system.

This tree was pulled out of a garden with one hand, about three years after it was incorrectly planted without fixing the obvious root girdling that still persists.

This tree was pulled out of a garden with one hand, about three years after it was incorrectly planted without fixing the obvious root girdling that still persists.

If root girdling is present, some roots may head off in new directions, but the circling roots will continue to do laps of the tree, eventually they can literally strangle the tree, or create a point of weakness causing the tree to fall over. Tree roots must be encouraged to grow away from the trunk, into the surrounding soil in search of water and nutrients. The best way to know this will happen is to remove all of the potting mix from the roots at planting time.

These Magnolia ‘Little Gem’ have been grown to perfection, the roots reaching just to the sides of the pot, but no further so they have not begun to circle.

These Magnolia ‘Little Gem’ have been grown to perfection, the roots reaching just to the sides of the pot, but no further so they have not begun to circle.

Remove as much potting mix from the trees to be planted as possible, and inspect the roots carefully. Any circling or crossed roots should be CUT with sharp, clean secateurs as squarely as possible to leave as small a wound as possible to reduce the chance of infection. This is the best possible solution to poorly developed root systems. If the tree does not recover, it is better to find out while they are still a manageable size rather than leaving the problem to get worse, and more difficult to handle when the tree gets bigger.

In some cases, more drastic action may be necessary, like cutting up a too-tight root ball with a spade or even a tomahawk. The shrub pictured below can handle this treatment. It will not get to tree-size anyway, so it’s not such an issue, but I felt the need to encourage lateral root developments by this ‘pruning’ method, and break up the pot shape which had it trapped.

Sometimes more serious methods are required to correct pot bound roots, can you dig it?

Sometimes more serious methods are required to correct pot bound roots, can you dig it?

So many gardening books and advice warns people from “disturbing” the roots of trees at planting, or of “tickling” them a bit. I strongly recommend a more heavy handed approach. Remove as much potting mix from the soil as possible, physically cut circling roots or roots growing the ‘wrong way’. Roots should ideally grow in a radial pattern as evenly spaced around the trunk as possible.  The potting mix can be sprinkled around the tree as mulch after you have planted it where it is to grow, any left over fertiliser will still give the tree a boost, but only after the roots have left their ‘comfort zone’ to find it.

There is no such thing as a perfect tree, but if you are not afraid of damaging “fragile” roots, the plants are more likely to get a good start, and grow better for years to come. Now I have to figure out where I will put the baby Bunyas so they have a chance to reach their full potential, long after I am gone!

 

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Stu Burns

About Stu Burns

Stu Burns has been gardening professionally for over 20 years, growing indigenous plants and edibles with equal passion. A former lecturer for the University of Melbourne at Burnley college, he taught a broad range of science and practical horticulture subjects. He is a horticultural consultant for domestic and commercial landscapes (trading as Garden Doctor Consulting), a presenter on Melbourne's Radio 3CR, and blogs at Garden Doctor, where he gives practical gardening advice and discusses broader contemporary issues affecting horticulture, agriculture and ecology.

4 thoughts on “Putting down roots

  1. Pam on said:

    Hi Stu
    I agree with you entirely. As an adjunct to your advice re planting in the ground I relate the following experience. I have a 1.5mt tall cumquat in a pot and when it was looking quite ordinary last year, with great trepidation, I removed all the potting mix, pruned the root ball by about half and replanted it in the same pot with new mix. It responded with renewed vigour almost immediately and has never looked back.

  2. Stu Burns on said:

    Sounds like almost bonsai techniques at work there. But as I said, trees are pretty tough. The worst thing you can do is coddle them.

  3. jeff howes on said:

    Great advice and all gardeners especially new gardens should know.

    When purchasing plants from a nursery I knock the pot off any plants that I suspect are root bound, if so I do not purchase (yes I return the pot to the plant).
    Jeff

    • Stu Burns on said:

      Definitely worth inspecting roots at the nursery before buying. A good nursery will not mind, either.

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