Thursday, March 14, 2019

How Long do Fancy Soil Materials Hold Water?

I never planned to share this.
But I did a home test of some soil additives and it might be useful to you.

Especially rock gardeners, orchid growers, bonsai enthusiasts and green roof builders have been more and more embracing permeable aggregates. They are a wide array, like Expanded Shale (Utelite in Utah), Expanded slate (Permatill in North Carolina),  the porous but fired ceramic (Seramis in Germany, UK, EU), Turface (the red of baseball diamonds), as well as older, well known natural materials like gravel made from shale stone, limestone, and gravel from scoria (lava rock) and pumice. You can also count diatomaceous earth in its non-pulverized form. 

Very, very, very fancy kitty litter:
This expanded shale made in Denver is used as the main component of soil for greenroofs. 
Expanded shale has been mixed into sand-based rock garden mixes at Denver Botanic, and makes up a third of my current favorite xeric/rock garden seed pot mix. It has been sold in bulk by nurseries and comes in different screened sizes.

All of these "gravels," natural or manmade, hold water and nutrients, to varying degrees. What I want to share was a fun home science project from a few years ago in which I wanted to know how much and for how long water was held by a variety of these available materials.  So I filled pots with them, having been dried to air temperature in the house for months.  They were each soaked with water, allowed to drain a set time, and then weighed daily for their water weight for 25 days.  My "science" was not airtight on this, but I tried to mimic good practices on my kitchen table. I know- I forgot a control pot that was not wetted, which would have ensured that my thift-store kitchen scale wasn't inaccurate.

Let's cut to the chase.

Turface held the most water, by weight, and for the longest time. It's comparable to expanded shale.

The first graph is simply the weight of each material every day after being soaked.
The second abridged graph is the weight of the water alone, and as you can see, some of the materials still had water trapped inside the aggregates at the end of my "study", 25 days later.

My deeply scientific label "hydropebble things" are ceramic pebbles used in hydroponics and orchid growing, the size of marbles. They would be useless for alpine and xeric plants but do a great job for orchids and hydroponics watered frequently. My "pink shale" is a 1/2" screened gravel crushed from pink shale rocks that I think are quarried in Wyoming and sold in landscape yards here in Western Colorado. The "Bond Pumice" is actually scoria (pumice and scoria are geologically different, I would learn) mined in Colorado, but common around earth as a normally black or red "lava rock" used in cactus mixes, et cetera. Utelite is the brand of expanded shale manufactured in Salt Lake City and used in their green-roofs there and probably in architectural concrete. The Turface came from a bag that was meant to go to a playing field. It's more expensive per weight but is mercifully available in a bag most anywhere people play baseball.

These red scoria chunks are screened a bit too large for use in small containers; 
1/2 inch (1.5cm) size is better.

This isn't a new idea, but it's more popular, that's for sure. The old school version was crushed flower pots, which were terra cotta: able to absorb water but were in little gravelly chunks to the consistency of kitty litter, allowing air and water to pass and drain around them.

Know that the test used these materials alone in pots, with air spaces between their particles. If these materials were used in a mix, especially one with peat or other fine materials, those fines would fill the gaps and certainly transport water around a container and change the way it is released and evaporates, which adds a big layer of complexity to how such permeable materials work when they are merely one component of a mix.

Also know that this doesn't say anything about the nutrient holding abilities of these materials, which probably varies dramatically between them, and would be lab tested as CEC, or Cation Exchange Capacity. What is so attractive about these materials is that they can hold nutrients without being organic matter, which is useful when we are growing plants from rocky places and aridisols, et cetera. Such plants are often sensitive to fungus and bacteria which thrive in a rich organic nutrient environment. Permeable aggregates also don't break down and can be sterilized for re-use.

I am too lazy to write any further depth, as I just wrote a chapter on it for our book, but this graph has been sitting around my computer for a while begging to be shared with folks who have been playing with these materials and would stand to learn from it.  I hope it is useful to you, friends.

Happy Spring and "Media Mania," (the season when you obsess over potting mixes)

Manfreda maculosa seedlings in the "trinity" of equal parts peat-based seed mix (Promix), perlite, and expanded shale.

Wednesday, February 27, 2019


 Echinocereus triglochidiantus f. inermis

I just read that Escobaria vivapara grows most western states and three provinces in Canada. CANADA.  Those cold, windy ones in the middle.  Not a houseplant.

Escobaria sneedii
Wasn't going to leave this gem at our old rental.  That's came with us. I chopped it to pieces which are all a bunch of babies now.

Sexxxy. Aw, come to daddy. 
Need me to help ya down with a front-end-loader next time I come visit? Yeah, you can come live in my front yard.

Mammillaria meiacantha

A White Sands Echinocereus becomes the host to Castilleja integra in a garden I did for a friend.

Echinocereus x roetterii

Hard Candy: Apex photos

June is perhaps as good as May for the APEX crevice garden.

Junellia succulentifolia; evergreen dwarf shrub, smells like a bag of gym socks.

Acantholimon venustum is the most common, greenish species to tolerate wetter climates. Ours looks like it wants to die now that the park fixed their years-old leaky drinking fountain nearby.  Agave kaibabensis and Maihenia poepiggii share the frame.

Maihuenia poeppigiii fruit.
It had green fruit on it in October, and I was going to leave them when cactus guru Rod Haenni said a more polite version of "They're ripe already, dummie, collect them before some bastard steals them." Sure enough: full of beautiful black, beady, glossy seeds. The seeds have been shared with growers and seed exchanges.

Buns in buns: Heterotheca jonesii seedling in Asperula gussonii
Not a common plant, Kintgen must have given me this Scabiosa graminifolia var. compacta.  It seems rare in gardens, but reblooms and reseeds in the garden like a hexane explosion. I have had to scrape up seedlings in winter.  

We get hypnotized by the Undauted Muhly Grass' pink autumn symphony, but let's not forget that Muhlenbergia reverchonii is an excellent, perfect rich-green clumpgrass until then.  More clumpgrass in steppe gardens, I say. 
Call to action.  Expect a ranting post on that.

Let's Gorge our Eyes and get Hyper for Spring.

Corydalis shanginii ssp. ainii with Aquilegia saximontana behind.

If you were curious, as one may never see a Manzanita (Arctostaphylos) seedling in real life, this is what one looks like before it dies. 
To date, I've got one living plant grown from seed.

The stickleaf family has christmas-tree shaped velcro hairs. Look'em up.

Townsendia cf. incana . North of Grand Junction, Colorado.

Allium macropetalum is often the first thing to bloom in March after the very first flowers here: humble desert parsleys.

Tulipa linifolia. Good cheese for the rock garden.

Linum cariense or aretiodes. I get so focused on planting the really important stuff I forget to record the name.  Anyone able to help me out?
In leaf.

A Buckthorn for the crevice garden. Because it's a natural limestone crevice dweller in the wild in Southern Europe.  Rhamnus pumila. Just soak up that bright green skittle.
Sunscapes has sold it the last few years. They are dioecious: plants are either boys or girls. Potted plants seemed to get infected with a root fungus that would hang with them for a while and then murder them.  I'll keep killing 5 at a time to get one of them to stay for posterity. They creep over rocks with their amazing gnarled tiny tree trunks. Self-bonsai. I realized a great use for this plant (in some public gardens I was working in) is where you need a good green in a place that is terribly exposed in winter. No problem- this guy (or gal) is deciduous and opts out of having to deal with winter.

Lepidium nanum, R.I.P. 
Let this be a lesson.  If you've proudly not watered a garden for five years, but  this year is a dangerously dry year, water your damn garden (Just once, even!) to save your plants.

'Firespinner' at Montrose Botanic

A hyrbid Sax at Dom's in Colorado Springs.

Erigeron compactus might be my new favorite Fleabane.
No. It is.

Leptodactylon watsonii.

Largest one I've seen in this state.

Scutellaria orientalis. It grows on road-cuts all over Asia, and in the garden blooms for so long you forget how long it does.  A bajillion forms and subspecies, this might be var. pinnatifida or a garden hybrid thereof.  Easy from cuttings.

Junellia succulentifolia, Agave parryi, Onosma sp.

Penstemon eatonii/barbatus hybrid?

Cornus kousa in a friend's garden.  North Side of a house.

Castilleja scabrida is most apt to succeed in a trough- here at Betty Ford Alpine Gardens.

Gentiana dahurica. My godsend.

I've killed every alpine Gentian I've ever tried here in the semi-desert. I plant them, crying. Again. And again.  I had one bloom. Once. With one flower. And then it died.  I think 105 F (41C) is just too hot no matter how much you water.  Finally- a part sun/ dry shade Gentiana. I don't care if the flowers aren't those tuba-sized G. acaulis you all can grow. It's true blue; look at it compared to other bastard blues on the right. They grow flats of this living sapphire at the local Valley Grown Nursery and no one buys it. I saw it naturalizing in grass under aspen in a mountain town in Colorado recently- the summers get dry up there, even.  This is the one, beloved.  Get you some.

Erigeron vagus in the Maroon Bells of Colorado.

A good mountain bike crash and hitting my head gave me the revelation for my first plant breeding. Behold, the dragonlemon.

Have another bowl.

Seedling Dionysia aretioides. Just North of a rock, sandy loam (9% silt) with no organics added. It gets a kiss of sun in high summer and just survives it. Watered weekly in the heat.  I'll try again to pollinate my older plant with this next year. Excellent fragrance. Like diving into a sea of fruit punch.

Dionysia aretioides in Colorado.
Ye old plant next to Sedum spathulifolium. Neither want our sun.
The Saxifrage is dead now, bringing it back to a total of zero in my own garden.

Dionysia involucrata 's bloom evades the focus on a phone camera. 
There is a new year's resolution to take less crappy photos.

Ages dark pink.  shadow of a north rock. Coarse sand with a little compost, but a few inches below that is heavy clay, which certainly gets it through dry spells in summer.

Dionysia aretioides takes from cuttings taken November, with hormone, in perlite, given gentle bottom heat and daily misting with all the other cuttings. I was sloppy and got these two out of 6 cuttings. While this is the most common species in cultivation, it's not easy to replace in Colorado. DBG grew piles of it for a moment and I'm glad I bought one.