How do plants work?

Just to recap – I am on a journey to understanding my sandy soil that has taken me into the murky depths of soil and plant science to find clarity.  I am trying to understand the reason behind things, so it makes sense as to why we do things.  Just saying plants absorb nutrients from the soil is all good and well when you have perfect soil, but when it needs help to ensure a perfect crop, understanding the mechanics behind it helps to make my actions as a gardener more effective.  I’ve spent some time poking about on the great big internet and with each revelation of understanding I was like a toddler asking, ‘but why?’ Which took me deeper in my understanding of what is going on in this new land I am now the guardian of.

So today we are starting where I ended up in my research.  My ‘but why’s’ took me on a journey from the soil to the plant, so explaining the way back should make it easier to understand.

Everyone knows plants get their energy from the sun and convert it to plant food in the leaves with photosynthesis.  This starts being introduced to small kids at school – that and the life cycle of a monarch butterfly.  I remember wearing out my best friend’s orange colouring in pencil on that project…  opps sorry buddy.    As my education progressed the layers of plant knowledge increased, and I can draw the internal structure of a leaf, its cell structure as well as the inside a chloroplast where the photosynthesis occurs within the cell with my eyes shut.  It just stuck.

It is fascinating, and to understand the internal structure of the plant does more than just understand how it works, it also helps to understand the impact of how we treat the plants.  For example, a common remedy for plant pests is to whip up a concoction which often includes liquid soap.  So, the natural liquid soap to grab is dishwash liquid… its soapy, it’ll do.  But the thing is, it isn’t soap – it is a detergent with loads of ingredients with the aim of stripping grease, fats, waxes and oils off your plates. It isn’t soap.  Soap is made from fatty acids from animal fats or vegetable oils.  I can draw the Triglyceride structure with my eyes shut too!  (Triglycerides are the molecules we like to call fat and proper soap is made from them.)  Insecticidal soaps, in water, kill some common soft bodied insects on contact and do little harm to the plant.  However, if you know anything about leaf structure you will realise that most plants have a waxy layer to help prevent moisture loss from the leaves and to use a detergent soap instead of a proper fatty soap will strip this protective layer from the leaves making the plant more vulnerable to diseases.  There are so many side tracking topics that are handy to know when delving into the complex lifestyles of our horticultural companions, but I need to come back to the facts of how plants operate in sandy soil.

Ok where were we.  Plants create their own energy from the sun, carbon dioxide and water with photosynthesis, in the form of carbohydrate sugars, with oxygen as a by-product.  The sugars are transported about the plant to the leaves, stems and roots in a pipe like network called the phloem.  It is a one way system sending the sugars down the plant to where they are needed.

Beside the phloem is another pipe network called the xylem and it comes up from the roots and is the one we are more interested in, as part of our journey to understanding the soil.  The xylem is the main pathway water takes through the plant, drawing up soil nutrients to take with it, to deliver them to where they are needed in the plant.

This water flow process is called Transpiration.  Plants take up a considerable amount of water from the soil, but they don’t actually need all the water they absorb and most of it is lost through the pores in their leaves, called stomata, as water vapour.  The main job for stomata is allow the carbon dioxide in for Photosynthesis as well as being a handy outlet for the water.  This controlled loss of water in the leaves acts as a kind of pump to draw the water up from the roots with capillary action.  As the moisture is lost more is drawn up into the leaf to replace it, pulling it upwards against the force of gravity and distributing soil nutrients with it as it goes and using what it needs for photosynthesis and then pretty much ejecting the rest.  It is a pretty impressive system.

There is much more to it than I’ve outlined, but essentially what we are interested in is the water function – apart from having some specific uses within the plant, like in making energy and other things like keeping cells nice and plump so the plants stay upright and don’t wilt and other things. The way it is used like a giant conveyor belt to deliver the nutrients from the roots to the tops.  A lack of water in the soil can interrupt this flow and cause harm to the plant.

So that is why it is important to have a soil that can retain water well, and why if I’m to have a successful garden I need to modify my sandy soil, because it isn’t all that good at holding on to water.  And this is where I arrived when I asked, ‘what happens once the nutrients get in the plant?’

But we are always left with the fact – the roots absorb the nutrients and water.  But my next questions were – that is all well and good, but how?  It turned out this was really cool and could make a great space-based action hero cartoon if I was any good at drawing and stop motion filming.

Come again soon – I will try to explain my understanding the how’s behind this magic ‘absorption.’

Sarah the Gardener  : o)