I hope this is the right place to ask.
I am going to prepare some raised beds out in the garden (probably a few layers of old bricks around for walls) and I want to mix something in the soil to make it more alpine-like.
Problem is, I don't know what.
I know the English words, but I have no idea what exactly I can find around here.
Best is granite?
What size?
Can someone have a look at this site and suggest something?
Probably for mixing in the soil a size is good, and for "topping" another one?
I am gonna have a huge collection of Sempervivums (judging by the millions of seedlings I have now) and hopefully some Saxifraga and Sedum and Androsace and a few more.

And, what would be the approx. ratio? half garden soil and half such gravel/grit? Or it's too much grit?

Also... underneath the 20-30 cm of depth, should I put some kind of cloth, fabric to suppress any weeds?

OK. Here's one of the sites I found.
http://www.afacerist.ro/catalo...

As a note, they say this stuff is used for ASPHALT?

When I plant alpines and rock garden plans---
I use what is called "Traction sand".
It is available only in winter here.
It has a mix of particle sizes probably from 1mm up to 5mm I am guessing.

Thanks Caroline...sounds about "right"

Good question Calin. I've always wondered about specific ratios and things as well.
Perhaps @valleylynn will stop by and give us some advice?
She's always very helpful.

Or maybe just post this in the semp forum, so all over there can give their opinion?
I have my opinions, but I am much too new to these types of plants to actually call it an "informed opinion."

Good luck,
J.C.

Just got home.
Calin that is granite on the link you gave us. Great to use for your semp beds.
This will give you an idea of the size I use. I also mix it into the soil. If you have heavy clay soil you have to be very careful about adding sand, unless you are also adding lots of compost and mixing it in well.


J.C. thank you for the call.

That the grit is used for asphalt is just fine for a garden purpose, too.

The granite grit is good, but you are not confined to it. If you find grit made from marble, limestone or something else, those should be fine, too. I use granite grit because that is what is available here. It is locally produced about a hundred miles away.

The stuff that is called traction sand here is on only very fine granules, not good for our use, and not what Caroline's traction sand is. Just know what your are getting.

I don't think you can get too much rock in a soil mix for alpines. That is what they grow in naturally. They will happily grow in ALL rock, but will grow much slower, due to a lack of nutrients to grow with. Sempervivums are very adaptable, as long as they get good drainage. A 50/50 mix, grit/soil, is probably a good mix to aim for alpines in genera. But again, semps can take most anything. I prefer a mix of grit sizes in the growing medium usually 4-8mm in pots, and 4mm to 2cm in troughs. When I make my cactus bed this season, I am going to do as a local cactus guru does: he uses all angular rock, 2-8cm, with just enough soil to fill the open spaces created by the rock.

For surface mulching in pots, I use a #2 grit. For a garden I would use much larger, at least 2cm. Be aware that using crushed rock (grit) or any angular rock, makes it very difficult to dig in, as opposed to rounded rocks. Perhaps that site also has rounded rocks, too. Most rock gardeners here prefer grit for pots and troughs, and rounded rocks for in the ground and raised bed applications.



You won't have to worry about weeds sprouting from seed at a 15cm or more depth. It won't happen. But you might if there are already established weeds growing there that you did not dig out or kill. They could have the energy to come up through from below. I would advise against using a fabric, if possible. It certainly wouldn't hurt any of the sempervivums, but many alpines will easily want to grow roots deeper than 20cm.

@Leftwood, Rick

>>>>all angular rock, 2-8cm, with just enough soil to fill the open spaces created by the rock.

Almost a perfect description of the "soil" on the house pad where I have been working to create a rose garden ...

I agree that weeds won't grow in it. I don't have to weed the areas I haven't cultivated.

I have a no-till garden simply because I was afraid the dense rock would break any tiller someone might try to use on it. I've improved the soil from the top down. The roses are doing fine. There is excellent drainage, yet the clay holds the moisture.

Smiles,
Lyn

Great explanation and photo Rick. I use the #2 & 3, and they have been working really well for me. The reason I like the granite is I was told the plants do get some mineral nutrients from it. What is your thoughts on that?

>>> I agree that weeds won't grow in it. I don't have to weed the areas I haven't cultivated.

Weeds won't sprout from seed below 15cm (and actually more like 3 -10cm). But weed seed near the surface will sprout.


>>>>all angular rock, 2-8cm, with just enough soil to fill the open spaces created by the rock.
Almost a perfect description of the "soil" on the house pad where I have been working to create a rose garden ... Whistling

That's exactly what he discovered: it's not important for his cold hardy cactus to have lean soil, just very good drainage (and warmish soil).


>>>The reason I like the granite is I was told the plants do get some mineral nutrients from it. What is your thoughts on that?

Definitely. In days gone by, gardeners knew this, too. It was normal for miners to periodically bring home rock dust to spread in their vegetable gardens.

Minerals from rock aren't as readily available as the soluble nutrients that we normally think of (NPK). For rock, more surface area means more mineral availability, and the smaller the particle, the more surface area. When I buy 50 pound bags of granite grit, there is always dusty small particles that settle at the bottom. For the grit I use as a surface dressing in pots or troughs, I sometimes sift out these smaller particles, too. But I always save all this to mix in the soil in pots or in the open garden. I am not sure what all the usable minerals are that are available granites or other rocks. Lori ( @growitall ) would know.

@Leftwood, Rick ....

This may sound like a strange question, but where do you buy the gravel/grit ? I live in a remote town in the mountains of northern California and I want to back fill the area where I goofed when I first made that bed by using compost in the planting area.

I am moving all of the plants out and want to bring the top of the bed back up to grade so that I no longer have a major low spot ... more like one half of the bed. I have some pure clay soil which the previous owner had imported for the lawn out in front of my home. I took out about three feet of lawn and stored the dirt in the back. I want to amend it with grit/rock/granite or whatever non-organic material that will work and use it for my back fill.

I am going to have to take a trip down the mountain to get the materials. All of it will have to be hauled up to the house pad level ... major labor on my part.

I, too, apologize, if I am posting to the wrong forum. Once I get those beds at grade and planted, I do plan to create a rock garden both down on the street level in front of my home and on the slope in that takes up most of the back yard. The slope will not need to be amended, but I do think I am going to have to add smaller rocks and planting material in with the boulders dumped down on the street level. Other projects.

Smiles,
Lyn

I usually get grit from the local coop, farm store, feed store, grain elevator, or tractor store. (Whatever you call them in your part of the country.) As areas build up with population, the availability is still there, but not as easily found. The coop nearest to me has merged with Ace Hardware. They still sell the good stuffs, but you don't find it listed as a coop in the phone book anymore....

I don't know why you want to use only non-organic materials for roses or other perennials (not alpines). That's what they like. That's what soil flora likes. That's the best way to hold nutrients. That's the easiest way to improve soil structure. The benefits go on and on. Yes, it does settle, so your initial build will include a higher grade than what you want in the end. And if you don't periodically add organic materials to you soil that naturally break down, you will end up with tired soil that roses and perennials won't like. You'll need to add fertilizers on a regular basis, and that will degrade the natural balance of soil flora, too. For plants that don't normally grow in in rock substrates, composty materials are practically cure all amendments.

Rick ...

>>>I usually get grit from the local coop, farm store, feed store, grain elevator, or tractor store

Thank you. The Ace Hardware store up here does not carry this kind material, nor does the one down in the valley, but I can find a farm store, feed store or tractor store down in the valley.

>>>>I don't know why you want to use only non-organic materials for roses or other perennials (not alpines). That's what they like. That's what soil flora likes. That's the best way to hold nutrients. That's the easiest way to improve soil structure. The benefits go on and on.

The answer is twofold ... 1) This was my first in-ground garden and I didn't know I couldn't create a rose garden. 2) I know roses. I didn't learn about them the way the traditional gardener learns about roses, but from the breeders of roses. In order to "play" with them, I had to learn the history of roses, the species roses ... many of which are found in alpine areas ..., the lineage of roses, the botany of roses and what they need to thrive. I know that roses are regional and what plant characteristics are required to survive and thrive in my garden. I've shovel pruned all of the roses that did not have those characteristics. I had been gifted with 150 roses, in bands, when I purchased this home as a housewarming gift. (Many of those roses were totally wrong for this garden.) I have worked on a rose database for more than ten years and learned about roses that I would have never found in a regular rose nursery.

I had had hands-on experience with probably more than a 1000 different cultivars by volunteering to work in rose nurseries and public gardens. I have first hand experience in learning how roses are produced in the fields, processed and ultimately marketed.

I am a novice gardener who happens to know more about roses than the average gardener.

>>>> Yes, it does settle, so your initial build will include a higher grade than what you want in the end. And if you don't periodically add organic materials to you soil that naturally break down, you will end up with tired soil that roses and perennials won't like.

Very true. I mulch twice a year, and often more during the heat of the summer, if the mulch breaks down too quickly. But over the years, with continuous mulching, watering properly and, yes, the addition of chemical nutrients, I have improved the native "soil" sufficiently so that it is far more viable. When I first started this garden, it would have been easier to use a jackhammer to dig my rose holes than to use a hand mattock. I perk tested each hole before planting. I didn't know I was supposed to prepare a whole bed. I can now dig in any of the rose beds with a trowel.

I did know that I didn't want raised beds because I didn't want the straight lines ... this house had far too many straight lines to please my eye ... and I didn't want to haul all of the material up from the street bed.

Since my first roses sunk, I quickly learned that when I back filled a planting hole, not to use organic material except in the top 10 inches because that is where the plant's feeder roots are located and to mound up the planting hole area, so that when it sunk, it sunk to the level I wanted for the rose. I also try to copy the native soil structure that was naturally there with a transition area between the potting soil where that held the roots of the rose I was planting.

One things I knew about roses is that I had to grow a larger root mass before planting because this allowed the plant to survive the stress in adapting to less than ideal conditions. All organic materials go on top since I am mimicking nature. Nature does not bury organic materials around the root base of plants. Nor do I.

>>>You'll need to add fertilizers on a regular basis, and that will degrade the natural balance of soil flora, too.

Yup. Not only fertilizers but also other nutrients/elements required to improve the performance of the plants. My soil is magnesium deficient and I have added magnesium sulfate to the planting areas. I also give the roses a kick start in spring with calcium nitrate.

Watering deeply and widely the day before feeding with any NPK fertilizer, or anything like calcium nitrate, allows the nitrate to stay within the root zone of the plant longer and to be available for the plants to take up more than would be possible without that practice.

Here's a photo of a rose that was planted in soil that was not amended with organic material before planting. In my opinion, it looks like it is doing quite well.



>>> For plants that don't normally grow in in rock substrates, composty materials are practically cure all amendments.

I am not sure what you mean by the above statement.

Smiles,
Lyn

I was under the impression that organic matter was somehow a nemesis, since you stated you only wanted non-organic amendments to your clay (non-organic) soil. You gave no indication that were talking about the soil layer below the rose root zone. If this was supposed to be self explanatory, or you clarified somewhere else that I missed, than I am really stupid, really sorry and really embarrassed. It all makes sense, now. Thank you for the clarification.

I've got to go to work now, and it's time to shut up anyway.
Rick

Rick, this was all very interesting reading and information. Don't stop.

There's so much you can learn ...
Some people suggested there's a difference between rounded/sharp grit. Suggesting the sharp one suits better alpines.
I am afraid to put too much rock cause this diminished moisture retention. I am thinking about the long periods of hot and dry that our summers seem to bring.
I am thinking also there's a difference between growing in a small crevice in a rock, with very little soil, on top of the mountain (but with enough precipitation and humidity) AND growing in a normal garden where most of the water will come from ME (again, in the summer).
Even this spring is VERY dry.
Adding to the fact that winter was dry...
it rained a couple days ago, but it was not enough.

FABRIC... I would place it for two reasons. There might be root-hardy weeds like thistle, or that grass with long underground stems/rhizomes. And If ever, I decide I need to plant something else there, I can remove the grit-amended soil knowing the limit is that fabric.

I'm very appreciative of all of the input on this thread. Thanks, everyone; I'm learning a lot.

RoseBlush1 said:

This may sound like a strange question, but where do you buy the gravel/grit ?

Lyn,

I don't know how much fill you need, or whether you want it bagged or piled, but if you need a truckload you might call a local building contractor, quarry, mulch yard or driveway handyman service.


The center of our yard is a natural watershed area. Several years ago, I built a permanent raised area across it to form a land bridge between our two houses. In my case, before I began I called the gentleman that gravels our driveways and asked for advice. He suggested using what's called "dirty fill" and explained that as dump trucks get loaded at the loading yard there's almost always some that spills over the top -this conglomeration of yard dirt, quarry dust and varying sizes of stone are periodically scraped into a pile and sold as dirty fill. It's usually sold at a very minimal cost, not much above the rate to deliver, and it sounds like it's just what you need. Yeah, it's difficult to deal with (larger pieces make shoveling it out a bear!), but it's already premixed, and settling after moving it to your desired area is minimal.
Our land bridge pathway has grown considerably narrower over the years as this mix has proven to be a perfect planting medium -now some of the best plants we have are growing there! (Roses, too .)

Otherwise, the big box stores sell bagged stone, but it doesn't go very far for the cost/aching back-work ratio.

Or, I wonder if Lava Rock would be easier to deal with in some situations? http://www.lowes.com/pd_381717...

Funny, until I did this search I didn't even know that it came in colors other than red! I really like the charcoal color.

@chelle

Yes, you are right about what I need.

>>>>before I began I called the gentleman that gravels our driveways and asked for advice. He suggested using what's called "dirty fill" and explained that as dump trucks get loaded at the loading yard there's almost always some that spills over the top -this conglomeration of yard dirt, quarry dust and varying sizes of stone are periodically scraped into a pile and sold as dirty fill.

Before I go down the mountain, I plan to contact our Road Department for what is called "waste cinder" to see if I can get it cheaper. For the smaller areas, I had planned to use lava rock mixed in with the soil I use for back fill. A geologist friend who I had up here to help me fix a drainage problem with the slope suggested that I use cinder/lava rock to mix with the clay because it is more porous and would capture some of the nutrients I add to the top of soil better as they moved through the soil when I watered.

I have already checked with the companies that sell various types of landscape materials up here and they all sell it by the ton. I am certain I don't need a ton of rocks ...

I want the back fill area to look and feel very much like the consistency of the rest of the soil in that bed. I plan to just leave it there all summer and next winter with a top layer of mulch. The Road Department may also have some material they use to chip seal many of the roads up here that they consider to be waste material, too. I am trying to correct one of my novice mistakes where I accidentally created that low spot.

I am going to follow @Leftwood, Rick's suggestion to mound it up and give it time to settle, before I do any planting in that bed.

>>>>best plants we have are growing there! Hilarious! (Roses, too Big Grin .)

Yes, the roses truly like this kind of "soil" in that it has wonderful drainage and the clay holds the moisture for them. I was quite surprised that they would do so well in soil that was more dense rock than soil. In a way, it's kind of like planting in a peculation pond. Of course, it is nutrient poor, but I have found that it is easier to correct the nutrient needs of plants than it is to correct drainage.

>>>>bagged stone, but it doesn't go very far for the cost/aching back-work ratio.

It doesn't matter where I get the stones ... everything has to be hauled up to the house pad level. After I fix this mistake, I am going to try to find plants that like the soil I have and quit trying to plant things where I have to haul heavy stuff up from the street level.

Thank you for the suggestions ....

Smiles,
Lyn

More great information.

How about the planting medium information on this page? http://www.geoscapenursery.com...

Does it sound reasonable to those of you who have set up your own rock gardens? I've yet to build one, but I need to do so soon.