Watering With Capillary Action

This might be more an A-Level sciences question but how does Capillary Action function?

So as far as I understand water functions in such a way that water molecules 'draw' neighbouring molecules towards them. This means that as long as plants are stood on a base that is kept wet even if the plants are comparatively large and tall water will be drawn up to the top of the pots.

But how does this actually function? if you had a large pot containing a seedling and it was stood in water would the pot itself need to be moist before drawing up water? Is this an efficient way of keeping seedlings moist?

I have some pots with capillary matting (special matting designed to be kept damp) but how easy is it to make a capillary system ourselves? I was wondering if the same principle would apply if I used a plastic container, with a little water pooled at the bottom, and set a standard plant pot inside it to stand in the water (provided a glorious illustration below) if this would also work? I've always heard conflicting things about standing plants in water however; my grandmother used to always insist it was the best way of watering plants however i've always been told it leads to roots rotting; is there a difference between doing this with seeds that haven't developed roots and developed plants?

Lot's of factors in play here, most importantly being the individual plant species water availability preferences (some like "wet feet", others don't and your soil makeup - any good potting soil, compost, etc. will have lots of carbonaceous(dead plant) material that will absorb, retain, and release moisture over time.  No single plant, soil type, or capillary system will be foolproof enough to "set it and forget it" long-term, so even the best system will need regular care and attention.

When you bottom-water a plant by putting it in a tray of water, it will saturate it from the bottom and work up to the top, even if the potting mix is dry. Some media, such as peat, will tend to repel water when totally dry, but I've found if it continues to be in contact with the water, it will eventually start soaking it up (it just takes a bit longer to get started).
The issue with watering only from the bottom is you eventually get built up salt, minerals, etc in the container; while watering from the top helps to leach them out before they get to levels detrimental to the plant. Personally, I like to bottom water when I let pots get too dry, which causes the peat-based soil to make a solid block, so water from the top just bounces off. But I usually just leave them in the water tray for a day or so to get it fully saturated and then remove. Otherwise I water from the top.
The biggest issue I've found from just leaving the pot in water is the potting media becomes waterlogged and turns anaerobic, which results in root rot. This is especially true for containers made of plastic or other materials that don't allow oxygen exchange in the media.
I've also found it depends on the plant. My carnivorous collection is perfectly happy in a bog garden, where there isn't any drainage and the media is always saturated. My juvenile bald cypress trees do great when I keep their containers in a tray of water during the growing season. Also, I tend to grow my trees I'm training for bonsai in plastic colanders to encourage root ramification, and they tend to do fine in trays of water (I assume because the colander allows enough air exchange to keep it from turning anaerobic).
So it really depends on many things, like media, container, plant type/growing preference, water source etc.

Thanks for the replies!

Sounds like its a bit of a mixed idea then on the one hand for some of my maritime species this'll probably be excellent but not too sure my herbs (mainly from the Mediterranean originally) will be happy with this!

M D Scott wrote:

Sounds like its a bit of a mixed idea then on the one hand for some of my maritime species this'll probably be excellent but not too sure my herbs (mainly from the Mediterranean originally) will be happy with this!

Yep, it just depends on the plant, it's natural growing environment, your environment, the container, and the potting medium. Maritime plants would probably be okay as long as the soil medium is comparable to what they naturally grow in. Something that typically grows in sandy, coastal soil would be more likely to rot in a peat-based mix.
The plants I've found to do the best with their pots sitting in water trays tend to be things that naturally grow in bogs/marshes; though my summers are so hot & dry, that I can get away with keeping some non-marsh plants in the water trays during June-Aug.
Some that do the best include: Taro/elephant ear, canna, hosta, bald cypress, willow, hibiscus, rattlebox, redwood, hydrangea, banana, Japanese maple, and some others. I've found some do fine in swampy soil with little oxygen while others start to rot as soon as the water starts to turn stagnant.
Trial & error is usually the best way to find out:)