April 30, 2008
1 May 2008 - Issue:001
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How Plants Grow
In this first issue of The Food Gardener I thought it may be useful to spend some time on a topic that most of us simply take for granted. Too often, I hear people say things like "Yes, plants are alive, but..." Of course, there really is no "But".Plants are everywhere. Any bare ground soon has something sprouting from it and so it may seem as if they just grow from soil a bit like crystals. I used to get similar responses when I went SCUBA diving in kelp beds and my dive buddies would complain that there wasn't much "life" down there. When I pointed out how much kelp there was they would say something like: "Yes, we know they are alive, but they are not really life".
There was an interesting research project done some years ago looking at the banding patterns on chromosomes. It was known that each species had its own unique pattern - like a kind of fingerprint - but the researchers wanted to know if there were any similarities. They looked at whole chromosome arms, so not just small similarities. They also compared things that were very different - human and onion chromosomes for example. They found that about 30% of the chromosome arms in plants had identical counterparts on human chromosomes.
This showed that we are not so different as we appear, but more importantly, that plants live and grow in exactly the same way we do. Their metabolism for respiration is the same and they use the energy from respiration for the same basic processes. Its just that a tree won't jump up and bite your leg off when you start up the chainsaw.
However, having established that plants are bona fide living things in exactly the same sense as animals and people are, then how do they grow?
Basic plant nutrition
Plants get their nutrients from the soil and they are simple mineral elements, so instead of Carbohydrate, Protein and Fat, they require Nitrogen, Phosphorus and Potassium; and instead of vitamins, they need trace elements. However, just as with human nutrition, all nutrients are essential - its just the balance that changes. For instance, we are told that Fat is bad, but really a diet with no fat at all would be as bad as one that has too much - we need a certain amount, but in balance with all the other nutrients in our diet.Plants are the same. Nitrogen makes them green and leafy, but too much makes them soft and prone to disease - just the way a high fat diet affects people!
If you are interested to know more about plant nutrition, here is a really good website to visit.
Of course, plants get most of their nutrients from the soil by absorbing them through their roots and this is where is gets really interesting. You see the anatomy of roots and shoots are so different it has led some to suggest that modern plants have evolved from two ancient forms that started out as symbiotic partners. There is no good evidence for this (that I have seen), but it does emphasize the point that to understand how plants grow, you need to understand how both shoots and roots grow, as their environmental requirements are so very different.
Naturally roots grow in soil - generally growing away from light - and have adapted to survive in what is a rather difficult environment. They have the problem of growing into this relatively hard and heavy medium and then getting moisture and nutrients out of it. No wonder then, it turns out they need a lot of help from the microbial community that also lives in the soil.
To ensure that conditions are just right for roots - and hence plant growth, we must start by looking at the physical environment within the soil.
Improving soil structure
To get hold of, and make best use of the nutrients in the soil, plants need a good environment in which their roots can grow and survive. To provide a suitable environment, we need to improve the soil structure.Actually, there is rather a bit more to plant growth than this, but these are the main points. As I have been writing this it has become clear that I should have a page or two at food-from-the-garden.com to cover the subject in more detail. However, if you have any questions or would like to know more, please feel free to contact me by replying to this email.