Best soil for a raised bed?

Michael Mace
Sat, 19 Jul 2014 20:20:02 PDT
I want to thank everyone who responded to my question about growing bulbs in
a raised bed. In addition to the replies on the list, I received two private
messages, one including photos!


I am still digesting all the interesting ideas. A couple of reactions and
followup questions.


>> Have you considered a sand bed?

Most of the messages suggested something along these lines. It's a really
interesting idea, and not something I would have thought of on my own. You
all were so persuasive that I'm leaning toward trying it, but I'm wondering
if anyone has done a sand bed for bulbs in a warm mediterranean climate like
California. I looked up sand beds online, and most of the examples are from
places like the UK that get summer rain. I can completely understand why a
sand bed would help preserve summer-dry plants in that climate, but in my
climate would the bulbs get too dessicated in the summer, and would the bed
dry out too fast in winter?


>> do not mix the sand with the clay top soil but let the sandy stuff stay
on type, the bulbs will sit in the sand and their roots tap the clay

Yes, that's exactly what I've been imagining. But then Bob said this:


>> Clay soils hold more water, but less is available to the plant because
the water binds to the clay particles like glue. My raised beds are piles of
sand and gravel, nothing else. The plants growing there require less
irrigation (in fact, none) than the plants growing in the heavy clay here.

Wow, Bob. This is why I've subscribed to this list for so long. You guys
teach me things I never would have guessed on my own.  


At this point, I feel like I almost have to try a sand bed, just to see
what'll happen. Will the roots grow throughout the sand, dive down into the
clay, or descend to the top of the clay and then spread horizontally?


>> if you have lots of earth worms they will mix it up over time and make
"concrete" so a really good geotextile liner is needed at the bottom.

Yikes, I had not thought of that one.


>> road sand tends to help it to dry out and drain better

Thanks, Ernie. I've never even heard of road sand, but I'll ask around. It
may not be something they stock in coastal California. I have looked at
various types of sand available near me, and it's frustrating. The "number
2" sand stocked by various rock yards around here varies enormously in
particle size and mineral types. 


>> ASTM C-33 spec sand aggregates have been most successful for us

Very helpful, Mark. I'll see if using that phrase gets me some consistent


>>As a project some years ago I started casting raised bed panels from
concrete or hypertufa with wire mesh inside.  

What a cool idea. I've made some hypertufa troughs in the past, but I never
thought of using it to make a bed. (By the way, other folks in the list, if
you've never made a hypertufa trough, it's a fun and easy project.)


Thanks again, gang!



San Jose, CA (zone 9, min temp 20F)

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