Monday, April 27, 2015

Roots Matter

The healthiest small trees are the ones that have “volunteered”, growing in soil of their own choice and having the freedom to develop their roots according to their own species growth rate and style.

Here is a local native tree of typical dry rainforest/vine scrub type (Cupaniopsis parvifolia). It was planted by a passing bird on a pile of rather loose mulch, from which I was could dig it out to show the complete root system down to the tiny hair roots. Note the seed, on which the seedling is still feeding, at what was the surface level of the mulch. Now notice that that the roots are already almost four times as long as the stem. 
A very close second best, when it comes to healthy trees with healthy roots, are those which are grown from seeds planted in situ. It's a good idea to put in a group of seeds in case some don't grow, care for them until they shoot, then remove all but the healthiest specimen. Ideally, the rejected plants are cut off rather than pulled out, so that there is no disturbance at all to the root of the chosen seedling.
A tree which starts its life in a seed tray or pot always risks having a less perfect root. This may do for shrubs, but is unsatisfactory for trees, which need deep, strong roots.
The compromised root of pot-grown plants may never be obvious, but is the reason for many poorly performing trees. Spending their babyhood in pots can cause them to insist on being multi-trunked when we want a single trunk, to be in poor health with "inexplicable" bits of die-back, to be more likely to blow over in a storm, or to have a shorter lifespan despite apparent good health. Many Australian plants have an undeserved reputation for being short-lived for this reason.
When we try to create healthy tree seedlings in pots, we need to consider how they prefer to grow. The prettiest potted tree in a nursery is not necessarily one that will make a good garden  plant. This particularly applies to native trees and shrubs indigenous to Australia’s inland. In most cases, the secret of these plants' drought hardiness lies in their "instinct" to get their roots deep down into the subsoil as fast as possible.
Good nursery practice for this kind of plant focusses on creating roots which are pointing directly downwards, with their growing tips ready to plunge deep as soon as they are put into the soil.
Having bought a tube-grown plant with impeccable roots, some buyers proceed to ruin it, by deciding to "look after" their new little plant "really well". With the best of intentions, they pot it on into bigger pot, and leave it for six months before planting it out.

Please don't!

Let me explain.
A really good local native tree or shrub, for this district (and any other district where rainfall is erratic) is one that has been grown in a tube that is as close to bottomless as it can be, without the potting mix actually falling out.

Contrast the bottom of this 2 inch (5cm) tube with the pot beside it.


Now notice the vertical lines, showing that inside the tube there are ribs designed to ensure that any root-tip that hits the side of the pot and shows a tendency to turn sideways, will be redirected downwards.
In a good native nursery seedlings in such tubes are then placed on a freely draining wire bench, and watered from above.

The result is that roots gallop to the bottom of the pot, where they are air-pruned, as shown here.

Notice that even this little native plant has already sent its roots to the bottom. Let’s have a closer look at it.

Who would guess, if they saw this infant tree in a “big" pot that its roots would already have suffered from being confined? They would have turned a corner as they hit the bottom of the pot, and the little plant would already be on the way to being pot-bound.

Now compare the tube with the pot from the side. At first glance, the big pot seems to be offering really generous root-room, doesn’t it? But what kind of root-room is it?

One thing we definitely don’t want our local plant species to do is to waste their time producing lots of root in the top five or six inches of soil.
When we do this to our native plants, we are being misled by the gardening traditions we brought from Britain and Europe. They were developed in places where rarely a week goes by without any rain, and having roots near the surface was an actual advantage. In most parts of Australia we need to help our newly planted garden plants to survive the real Aussie fact of frequent drying-out of the top layer of soil.

From the moment the seed germinates, we need to work with the trees' natural deep diving tendencies, rather than against it.

When we grow them in pots, rather than bottomless tubes, we force them to go against their own nature, wasting their time developing good root systems for growing in nursery conditions. They may be "nursery-pretty", but, despite their good genes for drought hardiness, they will be handicapped as soon as they are planted out. The unnatural tangle of close-to-the-surface roots with their tips pointing every which way means they will be more vulnerable to dying from soil moisture loss than a much smaller tube-grown plant would be.

What we want for planting out is something like this healthy little tree, Notice that its root tips have been trained to the bottom, ready to dive into the safer soil deep down as soon as it is planted. (Click on the photo for a closer look at them). Ideally the planting hole would be twice the depth of the tube, and not very wide. It would be filled with water once or twice, and the water allowed to soak away. Then a reservoir of water, consisting of a cup or two of well-soaked water crystals mixed with the soil in the bottom of the hole, would be positioned to sit below the newly planted tree.
With that kind of start in life, the plant will quickly develop the roots it wants, which grow rapidly to be much longer than the above-ground part of the plant. Once this is achieved, the top of the plant will start to grow as well.

Is it Pot-bound?
Some customers express concern that a plant like the above is “pot-bound” because they see that the soil is full of roots. It is not.
The crucial part of the expression “pot-bound” is “bound”. It doesn't just mean a pot full of healthy roots. The root tips in the above plant are not suffering from confinement at all. The little tube could actually afford to be very much more full of roots, without any hint of "binding", because the root tips have a sense of purpose.
"Pot-binding" means that the roots are going aimless round and round like a bandage, as is so often the case with roots in enclosed pots. They are quite often found to be heading back up to the top of the pot, in an attempt to escape from the mess. When planted, they may continue to grow round in the same pot-shaped space rather than spreading out to new ground. The advice that's sometimes given, to cut off the bottom centimetre of the pot-shaped plug of roots, or rip it up the sides to encourage the roots to start growing outwards, means that the poor little newly planted tree or shrub starts its new life in the ground with a need to heal its damaged roots first.

Consider the tube-versus-pot photo above, however. Transfer a tree from the tube to the pot and pot-binding would start to happen as soon as the roots hit the bottom. Increased volume of potting medium creates the illusion that the roots are better off , and with the kind of care that people give to plants in pots, the above-ground part of the plant would put on size, becoming "nursery-pretty". Once in the soil, that mish-mash of roots would take time to sort itself out, if it ever did. Most experienced gardeners know the disappointment of having put a healthy-looking pot-grown plant into their gardens, only to have it fail completely from root-binding.
A tube-grown plant would have much deeper roots than it's pot-grown friend in a matter of weeks.
Even with tubes, it is possible to create a pot-bound plant. The way to achieve this undesirable result would be to interfere with the free draining and the air-pruning features that the tube is designed for. Keeping it on a solid surface, where it might spend part of the time with the lower portion of the pot damp, can do it. Bottom watering does it even better. Sitting them in a tray of water is a good thing to do with them as they wait to be planted, but really shouldn't be inflicted on them for more than 24 hours.
So the best thing to do with a small plant bought in a tube is to get it into the ground as soon as possible.

Our native trees don’t like to be brought to the stage of maximum prettiness in their pots before they are planted out. Nor do they want a lot of leafy growth. What they need are gardeners who understand that optimum root development is the first priority.

Quick growth, strength, long life, and beauty will follow.

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