Sharp sand drainage properties
Grimvood
Posts: 2
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
Posts
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.