High water table

When planting in heavy clay soil, we are always advised to make a large hole, digging in plenty of grit and humus to aid drainage.

I can't see how this can work when you have a high water table. Water finds the route of least resistance I am told, so why doesn't this structurely opened up ground just fill with water from the top and sides, leaving the plants sitting in their own personal pond? If I did a hole in my garden and it rains, the hole fills with water to about an inch from the top, and stays there until some time after the weather improves.

In this situation, what is the best course of action?

 

Thats a fair question Chrysocolla. I think the answer is that if you really have a permanent water table that high it won't help. Adding humus and grit does help the drainage.

But there is another more subtle point that is the real reason. Strictly speaking, plants don't actually need drainage. If that were the case then hydroponics, where the plant's roots sit permanently in water, wouldn't work. What plants need is oxygen around the roots. They are a bit like people. Its not the water that kills them, its the lack of oxygen. If they don't get oxygen at the roots, plants drown. Once the roots have died they start to rot. But that happens after death, it is not the cause of death. The reason that hydroponics works is that the water is oxygenated in the same way as the water in a fish tank.

Clay particles are so fine (about one thousanth of the diameter of a grain of sand) that not only do they not let water pass, but when waterlogged they don't hold any oxygen either. Grit and humus, not only create drainage channels to allow the water to drain away, but they also create cavities that can hold tiny bubbles of air. And it's this air that keeps the plant alive rather than just the drainage.

 

Chrysocolla, look on the bright side you could build a fantastic pond.:D:thumb: 02

 

A fair point Peter, when we take cuttings of brugmansias we put them in a couple of inches of water to root, normally you need to change the water regularly to stop lt going off(stagnant) what we do to prevent this is to add an air stone and a small aquarium pump this keeps the water oxygenated and aids the development of roots you find the water doesn't need changeing.

 

That's interesting Walnut. Its sort of a hydroponic system for cuttings. What an air stone - is it a piece of pumice that holds air bubbles?

What I meant to add to the above is the irony of the situation. When a plant becomes waterlogged and dies, it actually dies of dehydration. :eek: When the roots are submerged in water they get no air. When the roots get no air they die. But when the plant loses its roots it has no way of drawing up water into the plant to replace the water lost in transpiration from its leaves. Hence it dies from dehydration.

"Water, water, everywhere, nor any drop to drink." :(

 

it's a diffuser Peter just breaks the air stream into small bubbles,it really makes a big difference cuttings root much quicker.

 

If you do as you say you correctly point out that you are simply creating a 'sump' in which your plant will drown
In conditions such as you have, if you are unable to take a drainage pipe away from the bottom of the planting hole to lower ground, then you must plant your plant on top of the ground and mound up the soil around it to provide the appropriate drainage. m It works a treat. Be sure to break up the soil beneath the plant first etc before doing so

 

" When a plant becomes waterlogged and dies, it actually dies of dehydration. "

Which is why over watered plants wilt. Very good explanation!

When working in heavy clay digging a hole and filling with good soil is not much help. YOu need to open and improve the all ground (which is a terrific job), or resort to raised beds and mounds, as Whisky suggested, planting in the original ground only tolerant plants (there ARE tolerant plants )

 

Thanks for the advice, especially to Peter. I now feel I have a better understanding of my soil and how to deal with it. Before I was just confused by advice because it didn't make sense to me.

I am very lucky to have a lovely, clay lined, wildlife pond, which is my favourite part of the garden. It is a very relaxing area and I love to watch all the wildlife that likes to live in it or visit it. Mind you, sounds like I need to do alot more digging to extend the lives of my plants, so won't be spending as much time by it!

 

Having thought about things during a sleepless night, I have a couple more questions.

Would I be better to use pea gravel or grit?

Also,in some areas, I have well established shrubs. Even these die in bad periods of wet. Would it be of benifit to them, to add gravel/grit and humus a bit away from them, or would the risk of damaging the roots out way the help it might give? If so, would it help a bit if I just put extra humus down and let the worms take it into the soil?

Unfortunately, my garden lies well below the level of the road and a piece of common land, so all the water drains down to my flat garden. Unfortunately I can't see a way of putting in a drainage system without unacceptable upheaval or upsetting the neighbours.

 

Gosh as I see things you must either raise the whole ground with a load of decent soil or build a decked area and turn the rest into a bog or water garden :(

 

Anything else you try is a waste of time and effort