Sand causing poor drainage??

My soil here is hard, black, compacted, clay, clay, clay... The first time I tried to amend a small space of it for a passion vine, drainage wasn't too good (and when my cat chewed through the poor thing at the base, I figured that was a sign to start over!). The second go-round, I practically broke my back digging up a much bigger area, and refilled with a mix of the original soil (25%); commercial peat compost (25%); composted cow manure (25%); & "play" sand (25%). I thought adding sand was supposed to help alleviate the poor drainage of clay soils, but this version seems to waterlog even worse than the first time! I did a little test - I put a handful of peat compost & soil into a small pot, soaked it, and compared that rate of drainage to the same stuff with a handful of sand added... the sand seemed to settle to the bottom of the pot and hold the water in! What gives??

Two things at work against thee here:

1. Capillary Science, mate.
It is why gravel really doesn't help either in pots. Actually hurts the drainage! The soil particles are close and hold onto the water more than the sand, so that interface where it settled is too coarse for the water to pass through from the clay. Example: If you took a cloth that was close-knit on one end and threadbare on the next and soaked the knit side, the water would hold to the knit side and not be absorbed from it by the thin side. Or think of a big-holed sponge and a small-holed sponge together. (If you want drainage in a pot, mix perlite into all of it)

2: Particle shape:
Sand's particle shape matches clay particle shape like microscipoc bricks, so that what it turns into! A brick-lined holding tank. Drainage is best improved by adding generous organic materials (like your composts) and not overtilling/mixing it, so that you don't break the aggregate/ mini-clods of soil. I have overwintered several passifloras here in places that show good drainage. They are quite sensitive to it, especially in winter. Hope this helps and you find something that works for you.
K. James

Thanks James for the great info!

Alright, so sand = bad, compost = good... lesson learned! So why have I read in some places that sand can be added to clay soils to improve drainage? A different kind of sand maybe?

When a landscaper is putting in a mountain of soil and he gets to engineer it all, (or a homeowner has a raised bed) he can do it- but there has to be a ratio of much more sand than there is clay! Perhaps authors just ditto things they have heard without trying them. If you use sand as a base for a pot mix, it drains better than a completely organic (soilless) mix.
But his business of putting a patch of sand under lavender plants for drainage looks good on paper with fine watercolor illustrations, but it doesn't work! I was at a soils lecture once where the speaker brought samples and clear funnels ans water to demonstrate how sand/gravel actually hampers drainage. We were all suprised because of how ingrained we were in our misconceptions! We figured that since sandy soils drain better, then hey...

There is a product called "greensand" that generates a great deal of controversy. The science that I have sifted out of all of the talk is this- it works in only certain types of clay, and is horrible in others. If it is worth anything, my personal opinion is this: Why buy a bagged wonderproduct when you can use something that is free that does what greensand does (and much more), but comes from your own kitchen/yard waste or an animal's rear-end?
But just as important, composting is awfully fun!
Kenton

The smallest sand particle, will cover dozens or thousands of clay particles. It's that simple. It's like throwing a bus size boulder on top of a layer of marble size nuggets or flakes. The "little guys" did drain, although slow, but when the huge chunk of rock is pressed and sealed over, the bad drainage gets worse.

Visit my page here...

http://www.mdvaden.com/articles.shtml

Then pick #28 on soil - it should explain it in basic detail.

You might find #26 useful if you will be adding a drain line.

I'm flabbergasted by this realization - I've read in so many "reliable" sources, many from books/articles written specifically for the TX gulf coast, to add sand (something like 30%) to our clay soil as a drainage amendment... Reading your responses though (as well as seeing it for myself), I don't doubt that you're right in your assessment of adding sand to clay. It's just amazing, though - wouldn't these people notice the poor results?

Kelly

Maybe more expert gardeners know about it than professional landscapers.

It can be deceptive, especially on golf courses, about 20 years ago. Only a handful of golf course superintendents knew about sand.

Many applied it to fairways, where the area firmed, but not many people noticed that the water was then diverted elsewhere. The sand firmed areas, but didn't help infiltration.

Some golf pros had to use it to enable carts to drive on fairways. The ones who understood, added drain lines or catch basins to the side and in low spots, to catch the water. They knew the sand was for a driving pad, not for water drainage.

On greens, the sand is used to fill the holes from aeration, so that those holes don't collapse.

New greens are probably 90% sand, so there's really no clay content to mess up. That's when sand drains much better, is when the soil is a sand soil - almost all sand.

Mr. Vaden; Great articles, mate. You are talented to present good science in clear and understandable laymans' terms.
You are an antithesis to a stereotype I have. I usuall wince at the term "landscaper" as visions of weed fabric/barrier, compacted subsoil, misplanted plants and overwatered grass fly in my mind's eye...

Once, before I knew better, I had a little raised patch with a fern in it that I built up. I used sand and compost, contained by bricks. The fern grew and did well. I read that sand as an amendment drained better, and I wonder why the heck a fern was doing so well where the drainage was supposed to be greater. The fact was that it had decreased drainage, which happened to be what the fern needed!
K. James