Sharp sand drainage properties

Hello there.

I wonder if someone could clear something up for me.

I'm sure I've heard of sharp sand being used to improve the drainage qualities of soil, so today when potting a new plant I added some to the compost. But when I started watering it the water just pooled on top for a while - much longer than with my other plants which don't have added sharp sand.

So I conducted an experiment - I took two identical pots, added soil from my garden to each, but to one pot I added a good trowel full of sharp sand and poured in a pint of water to both at the same time. The pot without sand had water pouring out of the bottom almost immediately, whereas the sharp sand pot took three or four seconds longer. Pools of water formed on top of both pots and disappeared at about the same time.

Not an exact science, admittedly, but it suggests to me that sharp sand is not to be used for improving the drainage qualities of soil. Is that right?

Thanks in advance.

James

James, sand does NOT improve drainage, in fact, as you have found out, it hampers drainage. If you want to improve drainage, use horticultural GRIT. Even better, add nothing.

Thanks for clearing that up 

You are welcome.

Are you sure it was sharp sand?

If it was sharp sand or horticulural sand, it doesn`t matter. Neither will improve drainage.

Fascinated by this. Are you then saying that  the advice and the practices of all those famous and successful growers of rare and difficult alpines have been wasting their time adding sharp sand (often Cornish silver sand which is as sharp as it comes) to their compost mixes? They have been doing this for the last 100 years or so.

This has always confused me, as we're told sandy soils drain too quickly, clay soils too slowly etc. 

We dug in one of those enormous ton bags of sand, no idea what kind, when we enlarged our big border & the plants all seeem very happy. I've read many times since that sand doesn't help drainage, it's grit that does. 

Also lots of seed or cuttings mixes I've read suggested half soil, half sand & the clematis montana cuttings I did a month or two ago for a friend in this mix have been successful. Could just be that montana is un-killable, even for me!

My guess is that sand holds water for a bit, but not much & not for very long. 

I have been reading around and asking about sharp sand and drainage.

That said, all sands improve drainage as they create channels or pores for the water to travel through. There are some fascinating, (and a lot of very dry  ) books on the subject - mainly aimed at sports turf management.

That is a quote from a Soil Management student.

So Daituom have you read these books?

Try this:

http://books.google.co.uk/books?id=szBM9Xi9vdMC&pg=PA33&lpg=PA33&dq=sand+soil+porosity&source=bl&ots=nVERXwSkDd&hl=en&sa=X&ved=0CDQQ6AEwAA#v=onepage&q=sand%20soil%20porosity&f=false

This is a simpler explanation (right hand column):

http://books.google.co.uk/books?id=anVTI5eBr28C&pg=PA125&lpg=PA125&dq=sand+improve+porosity&source=bl&ots=IRIUnsoNg2&hl=en&sa=X&ved=0CDoQ6AEwAQ#v=onepage&q=sand%20improve%20porosity&f=false

There's a difference between sharp sand (which is crushed rock;  In fact, it is fine grade grit) and natural sand, such as beach sand, which has rounded grains.  Beach sand (which is what builders use) should generallly be avoided for horticultural purposes.

If you have clay soil, adding sharp sand (as well as coarser types of grit, too) will improve it.  It is not simply a matter of improving drainage, but of improving the actual structure of the soil, (for example, so that it is better aereated, or to allow roots to penetrate more easly.)  The surfaces of the grains also change certain kinds of ion exchange which enables plant roots to take in some nutrients more easily.  The science of soil is extremely complex and very interesting.

In purely practical terms, and proven by my own experience, if you want to grow carrots and other root vegetables on clay soil, simply add sharp sand.  It works.

Exactly.

Our soil is silt over a sand substrate and even after all the rain we have had, the soil is now beginning to become very dry after only a week or so of no rain.

As said grain size and shape determine the ability (if that is the right word) of sand to allow water to pass through.

I needed to buy more for cuttings anyway & was faced with the choice of sharp sand, grit sand or silver sand.

I would have thought the grit sand would have had the largest particles, but the sharp sand actually looked like it had some grit pieces in too & said on the outside perfect for cuttings, so I bought that to try that this time. 

Does anyone know where Cornish silver sand and/or grit can be obtained these days? In the good old days it used to be available from a couple of local garden suppliers here in Oxfordshire, but seems to have now disappeared from the market.

As others have said, sharp sand is actually crushed rock, and has particles of various size in.  I've recently been reading about soil & soil improvers, as I'd like to start growing some veg next year, and autumn & winter is the perfect time for reading & planning what to do next year.  Lots of books say adding sand to clay soil helps, as it makes the soil more open, and helps to prevent a 'crust' forming when the soil starts to dry out, thus aiding drainage (otherwise the water just runs off the crust, and does not penetrate to the roots).  Adding any organic matter, and digging, helps to aid drainage, as it makes the soil more porous and opens up the structure. 

Sand DOES improve drainage, this is why you are advised to brush sand into your lawn every autumn, after removing dead grass by raking, and putting some holes in (or de-thatching and aerating to give them their Sunday names).

If you look at a bag of sharp sand and a bag of horticultural grit, there's not a great deal of difference - apart from the price, that is!

?Merseygrit?

Everywhere is soaking wet at the moment. What I've got here wouldn't be altered by any sort of grit or sand. A few dry weeks is what's needed.

From  what I have read, adding grit of any kind alone to clay soil can cause problems. The key is to add sufficient organic matter at the same time.  Alfalfa meal is a good alternative,  I add it in pellet version because it isn't available to me in loose form but as it decays it creates these mini pockets of fertile compost throughout the bed.