Pushing and pulling in the soil

Last updated 15:47 12/10/2012
pear blosssom
FLOWER POWER: Pear blossom grows on horizontal shoots.

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Yikes - scientists say the Earth's magnetic field is overdue for a flip, which, if it happened, would completely alter gravity as we know it.

They say the magnetic field is weakening and could disappear within 500 years before it then flips upside down.

In case you weren't aware, among the many advantages of having a magnetic field is that it shields Earth, and therefore us, from the Sun's deadly radiation.

And, in what seems to me something way more clever than anything we mere humans can do, animals use the magnetic field to navigate for migration. Turtles use it, along with birds, bees and some fish. And, perhaps, monarch butterflies while they are in flight on their extraordinary 6500-kilometre round-trip migration from Canada to Mexico each year.

Although they start their annual migration when the sun reaches about 57 degrees above the southern horizon, they are one of the few creatures on the planet that can orient themselves in both latitude and longitude during their migration.

It doesn't take a scientist to realise that they do this with way less brain ability than humans, who only managed to master this trick in the past few hundred years.

The magnetic field, gravity and solar radiation are, of course, invisible. I don't want to get too deep here, but although you may feel gravity and the heat of the sun, I find it intriguing that we can only know they're there, and therefore believe in their extraordinary powers, because we feel them. You can't actually see or touch solar radiation or gravity - you can only see the results of their power. It's all that stuff you study in school physics classes.

And so I have to believe that any changes in the magnetic field would have extraordinary effects on life as we know it, although I do find it hard to imagine a world without gravity or, being a summer lover, a world too hot to handle.

There is an upside, of course, for those of us fighting the sagging effects of gravitational pull on our butts - but basically, as scientists are predicting, it would be a big, bad new world we'd be facing.

One of the most dramatic effects would be on plant life. Has it ever occurred to you why plant shoots grow up and roots grow down? If you think animals are clever because they navigate using Earth's magnetic field, consider just how clever plants are to use gravity, without a brain, to know which way is up.

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It's called geotropism. This is the directional growth of plants in response to gravity, where roots have positive geotropism, growing down or towards the gravitational pull, and shoots have negative geotropism, growing away from gravity. Now, how clever is that?

Even though you might not know the name for it, keen gardeners will have seen the effects of geotropism when a plant is left to grow where it has fallen on its side. It quickly responds, with the shoots curving upwards while the roots will do their best to grow downwards.

While roots and shoots are regulated by geotropism, shoots are also affected by phototropism, or light-initiated growth. This is where naturally occurring plant hormones known as auxins direct growth towards light, an essential ingredient in plant growth.

Shoots in the light will straighten up, and those in shade will grow towards the light, aided by auxins which promote cell division and shoot extension towards that light.

To complicate matters, auxins also inhibit tip growth - which, for example, ensures just a single leader dominates in a conifer tree. But, as many of you will know, if you nip out the central leader (and therefore the auxins present), multiple leaders will compete for dominance until one outgrows the others to gain dominance as the new single, central leader.

Which is an important consideration in a little project I am embarking on this spring. Following inspiration from a fellow gardener, I'm attempting to espalier a pear tree on the top of a trunk into a bouquet of entwined, self-grafted shoots.

While it may sound a little eccentric, I regard the project as being like a living work of art, a horticultural challenge and, in the absence of any gnomes in my garden, as a bit of fun.

After careful consideration, I've selected a winter cole pear for my pet project. That's because it has the desirable wound recovery ability to cope with the cuts and grafts, and will readily bend and tie without breaking.

To encourage strong, but pliable, upright shoots to twist and bend, I've cut out the central leader, and will wait until late summer, when they've extended, to graft them back on each other.

Being a pear, it also produces an abundance of spring blossom, and in autumn, a crop of lovely brown fruit. Although it may be a bit old-fashioned and an acquired taste among pears, winter cole also needs to be left to hang and ripen on the tree well into winter (hence the name) for the full, juicy flavour.

Pears, like other pipfruit, produce flowers and fruit on horizontally growing shoots, the laterals that grow out from the main trunk - and so, by arching the shoots over each other and grafting the tips down to confuse them about which way is up, I'm hoping each branch will be covered in not only flowers but also fruit to make a dramatic display in the midwinter garden.

- © Fairfax NZ News

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