Making 12 cubic yards of xeric alpine soil....any help?

Welcome, Rino!
My thinking is that your 'mixed soil' is not a suitable substitute for peat moss. Peat is light and essentially sterile: it has no nutrients. A soil mix for alpines that is 1/3 (or even 1/5) nutrient-rich topsoil and compost will be too rich and cause the plants to grow out of character, long and leggy instead of the tight mats or buns that you're going for. It might also hold too much moisture at or near the surface of the soil where it could cause rotting of the drainage-loving plants. It could also encourage incursions of worms or other creatures that like an organic soil.
I'm far from an expert, but I have many plants doing well in a mix of 1 part topsoil to 9 parts coarse sand, and some people grow in beds of pure sand. I'd say go light on the topsoil.

Growing in a xeric bed in Texas is a world away from New England, but I'd agree with Jeremy and keep the soil to an absolute minimum. Sand and gravel will be fine as long as you feed the bed early each spring, and water deeply during the initial phase so the plants have a chance to get established. Once the bed is established, it may be possible to simply leave it alone with one supplementary feeding in the spring, but no water unless you are in an extended drought. But for the first year, water and water deeply, forcing the roots to seek out water by growing down. If you just wet the soil, the roots will spread out horizontally and you'll end up with a bunch of fried plants relatively quickly. But I'll wait for the desert experts to chime in for the 'final' word. Good luck with the garden and come back here often with reports and photographs.

Jeremy wrote:

Welcome, Rino!
My thinking is that your 'mixed soil' is not a suitable substitute for peat moss. Peat is light and essentially sterile: it has no nutrients. A soil mix for alpines that is 1/3 (or even 1/5) nutrient-rich topsoil and compost will be too rich and cause the plants to grow out of character, long and leggy instead of the tight mats or buns that you're going for. It might also hold too much moisture at or near the surface of the soil where it could cause rotting of the drainage-loving plants. It could also encourage incursions of worms or other creatures that like an organic soil.
I'm far from an expert, but I have many plants doing well in a mix of 1 part topsoil to 9 parts coarse sand, and some people grow in beds of pure sand. I'd say go light on the topsoil.

So do you think that if I buy:

1-1/4 cubic yards of topsoil and
11-3/4 cubic yards of coarse sand

for a total of 12 cubic feet,

then will I be fine with growing all the plants I have listed above, here in Dallas TX? I understand that here we have a Spring and Fall season that is full of thunderstorms and therefore a great well drained soil is best suited, but what about the period of the year that goes from June through October, when the average maximum temperature ranges between 90F and 100F? Wouldn't these plants have a hard time to grow in such a dry situation?

Either way, I really would listen to what you guys are telling me. I feel like this forum is the only good and reliable resource of practical information about alpines. This is the first time I am growing an alpine garden, and I guess I have been a little too naive on the soil requirements.
Good thing I am planning it so thoroughly!

Here is a quote from coldhardycactus dot com:
"SOIL PREPARATION:  In the dry climate of Colorado we actually have to water some cacti occasionally for them to thrive.  Our soils are typically heavy clays that do not drain well.  In most cases we would create raised beds by mounding the soil.  To the heavy clay we add 10% composted yard waste and 30-40% coarse sand (1/16th inch to 1/4 inch in diameter).  For Opuntias, this soil mixture provides adequate drainage with our average 15 inches of precipitation a year.  For species that require better drainage, we add more coarse sand (up to 60%).

Most of these cacti species prefer slightly alkaline soils.  If your soil is acidic, you will have to add crushed limestone or other forms of lime to correct the pH to somewhere between 7.0 and 8.0.  If you receive more than 20 inches of rain per year, you will want to increase the drainage material in your soil mix.  In extremely wet climates you may have to grow the plants in pots where they can be sheltered from the rain."

I guess you're probably right. Here in the Dallas metroplex rainfall reaches an average of 38 inches of rain per year. I guess I need to make sure I have a lot of sand!

This however brings me to ask what is the best sand I should use?
And this brings me to ask another further question: is this soil going to be good for succulents only, or will I be able to grow other herbaceous plants as well, such as Achillea, Alyssum, Anacyclus, Armeria, Dianthus, Hirpicum, Hymenoxys, Iberis, Nierembergia, Penstemon, Pulsatilla, Veronica, and so on?

I have these choices from my local quarry:

1) Crushed limestone (base material for packing)
2) Concrete coarse sand
3) Decomposite granite
4) Expanded shale
5) "Remix" (concrete sand and pea gravel)

I am wondering if these sand mixes would be good:

Sand Recipe 1:
1 part crushed limestone (is this better for alkaline soils than concrete sand???)
1 part expanded shale (I think expanded shale is a wonderful component, especially in sandy soils, because of it's property of both retaining water that can be available for plants during droughts and improving drainage)

Sand Recipe 2:
all "Remix" (but I have been told pea gravel should be avoided in rock gardens. Crushed gravel works better, so I am kind of reluctant about this choice).

This is the link to the quarry website page where it shows pictures of the types of sand:
http://www.whiz-q.com/Merchant2/merchant.mvc?Screen=CTGY&Category_Code=sandsoil

That is a lot of ground to cover.
I look at building a dry land bed more like layering a cake.
The upper say two to four inches should be very well drained. (1/4" and down gravel/sand material)below that you can add fines of loam or clay maybe 10%-20%  by volume to help hold a little moisture in a hot dry climate. Remember the roots will reach down to the subsoil eventually and use the subsurface moisture located there.  Excellent drainage and good air circulation at the crown is crucial, especially in hot humid climates. I agree that additives that are overly rich in nutrients will cause most dry-land plants to grow out of character but I do not use peat either. I find a mineral based mix is just fine. Most dry-land plants are not adapted to deal with the fungus and bacterial loads found in high humus soils. I do not fertilize my beds at all "Lean and Mean" works for me but other growers in wetter climates use light applications with good results.
I use a sharp sand/small gravel mix. Various sized gravels are mixed with the sharp sand in my differant beds. Any thing from 3/4 inch down to 1/8 inch are good. I use these mixes for the full depth of the bed adding some fines(20% normally) only in the lower layer. The size of gravel used or the exact portion of sand to gravel used can vary a lot. Normally I use three parts sand to one part gravel. It really all depends on the look you want Vs the ease of digging you want.
Thirty eight inches of rain a year is a lot in my book! I only get nine in a good year but I do irrigate  plants that require more than my climate supplies.  ;) You can irrigate if you feel the need but if your humidity is high in the summer I would not suggest a sprinkler system. Too much moisture on the leaves at night will promote rot in tight buns and cushions. I use drip irrigation and bury the tubes and emitters below the surface out of sight. I find a well placed 1/2 GPH emitter, turned on for two fifteen minute sessions a week, can supply the moisture required by multiple plants, within say two feet of it, especially if they are mature established specimens. I agree that new plants need a ready supply of moisture until they have a well established root system. I add most of my plants only in cool spring of fall weather, it requires much less individual attention. If you are moving plants in from the wild I strongly suggest doing it when they are still fully dormant in very early spring.

Quote:

is this soil going to be good for succulents only, or will I be able to grow other herbaceous plants as well, such as Achillea, Alyssum, Anacyclus, Armeria, Dianthus, Hirpicum, Hymenoxys, Iberis, Nierembergia, Penstemon, Pulsatilla, Veronica, and so on?

I don't see an issue with any of the plants you mentioned they should all do fine. If you feel the soil is too lean in any spot you can easily add a touch more loam/clay/peat/fertilizer etc.... to the planting hole.
There is no exact science just a lot of suggestions from growers in very differant climates.  Mine is High and Dry. Summers have cool low humidity nights, sunny high UV days and hot windy, afternoons.
Good luck and have fun!! ;)

Manfroni wrote:

1 part crushed limestone (is this better for alkaline soils than concrete sand???)

Yes, if you want to create alkaline conditions, you will need to add limestone.  Sand is normally primarily silica, which is essentially neutral pH.

Traditionally in the UK raised beds and even screes have often had significant amounts of loam and/or peat in them, but these have often been made by growers in the north with cooler and moister climate and more of an interest in plants from the Alps and Himalayas. Less people have grown more dryland alpines. I have only recently started growing more plants in a sand bed and it has been so much more successful that I would echo the advice of keeping the level of loam/peat to the minimum, if at all. Our rainfall is around 25", so quite low, but the biggest problem comes in the winter when we have no prolonged snow and the beds become too wet. In some places I give the plants winter cover; in others not. Top dressing with coarse grit helps a lot.

The bed I have, which is relatively small, has been one of the most stimulating features in the garden and makes me want to extend the idea. It would be fascinating to hear how you progress too.

Welcome to the Forum, Rino! 

I have also found that the traditional recommendations of soil mix is not lean enough.  It is easy to add more nutrient or water holding capacity to you soil after the fact, but going the opposite direction is comparatively difficult.  Some of the plants you mention, like penstemon, delosperma, echinocereus, don't tolerate richer soils well, while others that would prefer a little more nutrient rich soil will tolerate leaner soils.  Peter makes a very good point that what is respectable soil mix in the Northeast (for instance) may not be the best for your very different climate.

You may want to look at this in the NARGS Wiki:
http://nargs.org/nargswiki/tiki-index.php?page=Soil+for+Rock+Gardens+and...
It can help you get an idea of what we are talking about.

We hope to see more of you here on the forum.  It's a great place to exchange ideas, plants, photos, etc.!

You've certainly stirred people up with your request and I would echo what a lot of the others have said - use sand and gravel - and avoid adding peat. The principle is that with such a lean mix plants will form really extensive roots to cope - there will be far more underground than on top. Although as some people have said they may need supplementary watering until they get established. One thing you will need to do is make sure that the surface has a layer at the surface which is fairly stony that will help reduce evaporation and baking of the surface.

Having not actually seem and handled the materials at your local quarry (sounds like you do have good options there) I would have a really good look at the decomposed granite. Snag with limestone is that some things don't like it whereas very few things really have to have it - you might look at having the limestone as a band either crossing the bed or at one end.

As Tim Ingram said people in the UK have traditionally used loam and peat in the beds but there are quite a few people now building beds with just sand and gravel. I garden in the east of England with only around 20 inches of rain a year - recently we went two months with no rain at all (actually 3mm between March 1st and April 30th) and the plants in the sandbed - nothing like as big as yours - coped fine. Including things like western Astragalus, Eriogonum, mediterranean plants such as Aphyllanthes, and central Asian Iris.  

I know that you have much higher temperatures but you also have much higher humidity at times - our humidity is very low - so we are all giving you advice based on what we think we would do if we down there.

We are all really intrigued by how you get on - sounds such an exciting project - do take pictures of what you are doing because I would love to have a record of how you get on for the Rock Garden Quarterly and I'm certain other people would be equally intrigued.

Good luck

thank you guys! I have the entire summer to work on creating this garden before I will order my new cuties in September! we first have to finish to paint the front of the house and install those so-called EZ-flow French draining pipes so we avoid that the berm will convey the water toward the basement of the house. Actually I am going to start digging tonight since I killed the GMAT this morning and I have the entire weekend stress-free! Yay!

After evaluating the replies of you guys more expert than me, I think the definite soil choice will be crushed limestone and some concrete sand. absolutely as lean as possible to create the perfect alkaline environment for succulents and alpines. I will try to complete it as soon as possible so the berm soil will have time to get established before September.

I'll keep posting here with pictures of my work in progress. I think this post can be very useful for other people who live in the metroplex because I have the feeling I am going to be one of the few pioneers experimenting with an actual alpine garden in Texas! I can't wait to show it to my North Texas garden society too!

I can't advise you on rock garden in Texas but I looked through your wish list and recognised some plants ;D

Here is one of them growing in abundance in almost pure quartz sand, Armeria maritima. It also grows in cracks in the rocky outcroppings.

Those Armerias look wonderful in the wild! I have seen the white variety in San Francisco last January and I was amazed by the fact they bloomed in the cold of the winter. I picked one plant, but the problem is that these plants have a very long tap root and when I came home to Dallas I only had pots that were not long enough to contain the root in its entire length... so I curved the root to fit it in the pot, but the plant finally died last May when it started to become probably too warm outside. I think Armerias make such a long root to reach the water way low underground and a pot is not the best place to grow them in, especially where it is very hot in the Summer. In addition, I think the white variety is not nearly as hot-hardy as the pink variety.

Here is a picture I took when I saw them. Yes, I am gonna have Armerias in my garden!

Your picture could have been taken here in Norway ;)

I would say it is impossible to move Armeias from the wild. As you say they make a extremely long taproot and the root grows into crevices. The plant eventually die if the taproot is cut. I think they are not difficult from seed though.

The other reason why a taproot might be of advantage to an Armeria is that they often grow on cliffs, sometimes pretty solid but sometimes softer shales so the taproot will provide anchorage. A better way than trying to transplant one from the wild, or grow them from seed, might be to take cuttings - they root OK - that's why there are the named cultivars that nurseries sell.