Best sand for a rock garden

[Jan Jeddeloh]

I know the best sand is the mythical "coarse sand".  In my area of the world (the Pacific Northwest)  such a critter does not exist.  Believe me I've looked.  You get your choice of beach sand which is obviously a no go, mason sand which is quite fine, concrete sand or "fill" sand.  I'll elaborate on the last two after I've described my rock garden site.

We just had the sod stripped off our front yard.  The yard is slightly sloping and the indigenous soil is a heavy but rich clay.  When it's wet it's slicker than snot and you can easily ball it up.  My plan is to dump 6" (12cm or so) sand on top of it, add rocks, a top dressing of small gravel and call it a rock garden.  I'll add a little bit of starter compost and some slow release fertilizer when I plant so get plants started.  When I built my crevice garden a couple of years ago I used sand and gravel with a tiny bit of compost and slow release fertilizer. The plants love it.  I should mention we get about a meter of rain a year mostly falling between October and May.  Summers have little to no rain.  It's early June and the soil is already dry.  I'm not worried this mix will be too lean because the plant roots will hit pay dirt after six inches when they hit the clay soil.  The biggest problem with rock garden plants around here is drowning them. 

So back to the sand conundrum.  My two possibilities are concrete sand and fill sand.  Around here both are mined from old river beds.  Concrete sand is washed and has a few bits maybe 3mm wide.  The sand grains are fairly rounded so it compacts.  Fill sand is slightly coarser in the the few bits are bigger, up to a cm or so,  and vary more in size. It however isn't washed and has a brownish cast to it so it probably has more fines than fill sand.  Again a river based product So basically I have a couple of lousy choices to make the best of.  I suppose another option would be to get what's called quarter 10 gravel (1/4 inch crushed gravel  with the fines screened out) and till it into the sand.  This would be something of a hassle but not impossible.  This is essentially what I have in my crevice garden. 

So what does anyone think I should do when faced with my less than idea options? 

Thank you,
Jan Jeddeloh

[fermi de Sousa]

Hi Jan,
if you think "coarse sand" is hard to obtain, try to find "pea gravel"!
The best we can do here is get a "coarse sand" which sounds a bit like your "fill sand" and when I want to use it in potting mixes I sift it to remove the fines. Not something you could employ for an entire garden bed.
I suspect that your best option is using the fill sand and adding quarter 10 gravel to balance it out,
good luck,
fermi

[Tristan_He]

Hi Jan, that sounds like a pretty good plan to me, and quite similar to what I have done on my rockery. I use sharp sand from builders merchants, which is availabe in tonne bags and therefore pretty cheap (see photo below, standard pencil provides an impression of scale for grain size). I think this is roughly equivalent to your concreting sand? I can't say I've done any trials though.



Generally I find this type of sand works fine. Plants root well into it and with a little topsoil added it can retain some nutrients. Maybe you could try growing a few plants in both types of sand to see what works?

With all that clay maybe you should try growing Fritillaria pluriflora which is supposed to like this type of soil! 

Best wishes, Tristan

[CRSHEP0]

Jan, I sympathize with you.  I live in the East Bay, thirty miles west of San Francisco, and I  have been to many quarries looking for the same thing.  I drive up north to buy my sand from Hilson's in Central Point, Oregon. They will only sell you a quarter yard minimum.  But, it has air spaces, and different particle size.  One year I was desperate, and my husband and I went up to a dried up river bed, and brought home 5g buckets, which I had to sift out the fines, to get what I needed.  I would send a picture, but, I don't know how  to post I Phone pictures. Check out Hilson's, I seem to remember that they have more than one type of sand in their bins. I was there in April of 2021. I have been using their sand for over fifteen years.  Rick Lupp's (an incredible Alpine plantsman in Graham, Washington) had a recipe for alpine plants that was 9 parts sand, 5 parts peat moss, and 4 parts pumice. It did not work for me for my hot, dry climate, but might work for you.  Cecile

[Jan Jeddeloh]

Posting about my gravel problem has helped me clarify my mind about what I want to do.  I think my best bet is to go with a 50/50 mix of concrete sand or fill sand, which looks close to Tristan's construction sand, and quarter 10.  Quarter 10 is 1/4 inch crushed gravel with the fines screened out.  If I can get my sand and gravel place to mix in a wee bit of compost I will otherwise I'll just add a bit of potting mix in the area I plant.  The roots only have to go down 6" to hit nutritional pay dirt, namely the clay soil so I'm not too worried about nutrition.  When I plant in lean soil I mix in a bit of slow release fertilizer anyway.  It is so annoying that the sand and gravel industry does not cater to us rock gardeners.

Interesting that Fermi can't find pea gravel.  That's easy to find around here. Cecile unfortunately Hilson's is too far for me to go for gravel no matter how nice it is. I live in Portland so the transport cost would be astronomical.  Since you come up to that area regularly do you know about Kathy Allen and her garden and sales?  Fabulous garden, fabulous plants for sale.  I know Rick Lupp and yes his garden is fabulous.  Too bad he closed his nursery.

Jan

[Rick R.]

Is 6 inches deep enough?

This Erigeron compositus seedling isn't even one season old: