Growing medium for a crevice garden

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Novak
Title: Member
Joined: 2009-10-07

Maggi, thanks for the links! I've been spending a lot of time this week on the SRGC forum, learning a lot and getting a lot of inspiration. I'm thrilled to know that all those issues of the journal are available.

Janet
Philadelphia, Pennsylvania, zone 7a
Webmaster for the Delaware Valley Chapter (dvcnargs.org)

Novak
Title: Member
Joined: 2009-10-07

McGregor wrote:

Using tufa for crevice gardens is completely different to using much less porous rocks. Tufa will allow an exchange of moisture from itself to the compost surrounding it. The exposed surfaces of tufa will have higher evaporation than a non-porous rock so the moisture dynamics of a tufa rock garden are very different to a crevice garden built from something much less porous.... Using loam in the cracks is one way round the problem but it does not encourage deep root growth down the crevice in the same way that a better drained compost and less porous rock will.

Malcolm, this is a good point. Do you have a recommendation on the sort of mix to use with tufa?

At the moment, I'm leaning towards a mixture of 50% sand, 25% quarter-inch gravel, 25% loamy soil (dug from 4-12 inches below a former lawn, to avoid too much organic material). But I'm still open to advice.

Janet
Philadelphia, Pennsylvania, zone 7a
Webmaster for the Delaware Valley Chapter (dvcnargs.org)

Anne Spiegel
Title: Member
Joined: 2010-01-26

Most of my crevice gardens are built without any tufa - only one has tufa.  The mix used is lean and fast draining but there seems to be moisture on the rock surface below even when the top is very dry.  Since I grow a lot of drylanders this seems to work quite well.  The crevice sizes range from less than 1/2 inch to as much as 11/2 inches with stone chocks. 

McGregorUS
McGregorUS's picture
Title: Guest
Joined: 2009-12-18

Janet, I use sand/gravel mix with no loam. It's what Peter Korn does and if it's good enough for him it's good enough for me. Then I scout round and look for the drier and damper places, more sunny and more shady to decide which plants go where.

I have some pieces of tufa but not a tufa crevice garden - tufa is so scarce over here that I can't imagine anyone doing that.

I have seen peat blocks used to create crevice gardens. Again with sand/gravel as the fill.

Malcolm McGregor
Global Moderator/NARGS Editor
East Yorkshire, UK

Tim Ingram
Title: Member
Joined: 2011-04-27

Some great ideas - I like the revamped crevice beds in Maggi and Ian's garden, and the arrangement of troughs together. Those deep troughs based on vertical paving slabs must be ideal to provide a deep root run. I had never thought of using peat blocks in the way Malcolm suggests (I don't know how easy they are to get hold of?). In our dryish climate in the south they could be effective in holding a bank of moisture (Adrian Cooper succeeded in growing choice primulas, shortias etc. in a London garden using these, which surprised me). Very stimulating discussion!

Dr. Timothy John Ingram
Faversham, Kent, UK
I garden in a relatively hot and dry region (for the UK!), with an annual rainfall of around 25", winter lows of -10°C and summer highs of 30°C.
 

IMYoung
Title: Member
Joined: 2010-01-31

Janet wrote:

Maggi, thanks for the links! I've been spending a lot of time this week on the SRGC forum, learning a lot and getting a lot of inspiration. I'm thrilled to know that all those issues of the journal are available.

Happy to help, Janet

You'll see that for quite a few years the editor of the SRGC's  "The Rock Garden" was none other than current NARGS Editor, Malcolm McGregor  ;) 8)

Ian  and/or Margaret Young ( -here it is usually Margaret)

Aberdeen , North East Scotland, UK
Zone 8a

www.srgc.net

RickR
Title: Moderator
Joined: 2009-09-21

McGregor wrote:

Using tufa for crevice gardens is completely different to using much less porous rocks. Tufa will allow an exchange of moisture from itself to the compost surrounding it. The exposed surfaces of tufa will have higher evaporation than a non-porous rock so the moisture dynamics of a tufa rock garden are very different to a crevice garden built from something much less porous.

To go all the way along this route - image a crevice garden built with peat blocks. The peat will hold and give up moisture. Using loam in the cracks is one way round the problem but it does not encourage deep root growth down the crevice in the same way that a better drained compost and less porous rock will.

How fortuitous is the timing of this statement.  An acquaintance in another group recently posted some very interesting work he is involved in.  He is conducting tests that show how a root grows in a droplet of water on a dry surface, if and how it ventures outside the droplet edge, etc.  A very controlled environment. 

The gist of it is this:
He says the findings are only preliminary, as they have only done about 100 replicate tests, "But, so far, the data suggests that when the plant is happy (it has all the nutrients it needs) it will be less adventurous, it will be less prone to leave the droplet. On the other hand, if the plant is starved for nutrients, it seems more willing to push through the edge of the droplet."

Rick Rodich    zone 4a.    Annual precipitation ~24 inches
near Minneapolis, Minnesota, USA

Anne Spiegel
Title: Member
Joined: 2010-01-26

Rick, that's really interesting.  That seems to bear out my observations in the crevice gardens here.  My "clay marbles" are always well below the plant roots' immediate reach and the mix is very lean.  When plants have had to be removed the roots were quite deep and also clinging to the side of the rock, so that they almost had to be scraped away.  When I built the crevice gardens I had Zdenek's book with me at all times. similar to having Linc Foster's book with me when I built the rock gardens.  Always so much to learn!

RickR
Title: Moderator
Joined: 2009-09-21

Spiegel wrote:

When plants have had to be removed the roots were quite deep and also clinging to the side of the rock, so that they almost had to be scraped away. 

Yet another practical observation upheld by his project's preliminary findings:
When the roots ventured beyond the droplet edge on the dry surface, they pulled a film of water around themselves as they grew.  This would be analogous to the side of the rock.
"When we saw this, we thought that this has to do with the surface tension of water, which the root uses to carry water along on a dry surface. So we thought, why don’t we prevent the root to do so, by changing the surface tension of water. We changed the droplet into a gel (this is the kind of thing that can happen in soil in the presence of some organic matter or particulates).  What happens is the following...

"The root escapes and finds itself on a barebone dry surface and it switches completely growth behaviour. It starts forming a completely insane amount of root hairs. This is quite interesting because it shows an interesting experimental system that can display two radically different root developments in the same plant. I believe the plant is forming this large number of root hairs to collect water from the very humid atmosphere (a common strategy used, for example, by insects in the Namibia’s desert)."

Rick Rodich    zone 4a.    Annual precipitation ~24 inches
near Minneapolis, Minnesota, USA

IMYoung
Title: Member
Joined: 2010-01-31

Thank you these reports, Rick - full of interesting points. 8)

Ian  and/or Margaret Young ( -here it is usually Margaret)

Aberdeen , North East Scotland, UK
Zone 8a

www.srgc.net

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