Showing posts with label Diatomaceous earth. Show all posts
Showing posts with label Diatomaceous earth. Show all posts

Tuesday, September 29, 2009

Recipe for cactus soil mix

On various occasions I've been asked what growing media I'm using for my cactus plants. I don't have a set soil mix recipe as such – the mix is a continuous work in progress influenced by earlier results combined with input from friends, articles, etc (and sometimes laziness drives me to use whatever ingredients I have readily at hand ;-) Anyway, a few weeks ago I mixed a large batch of growing media and decided to document the details. If you have any comments or suggestions for improvement, please let me know.

Cactus soil mix
Cactus soil mix

As mentioned, I'm not religious regarding soil ingredients as long as the mix meets a few simple criteria. Good drainage and aeration is essential in any growing media used for raising cacti, still the growing media must have adequate moisture retention properties in order not to dry out too fast after you water it. Depending on the type of cacti you are growing you might vary the amount of organic matter (or omit it completely). I don't worry too much about nutrients in the soil – if you are using a pure mineral soil you'll have to supply most nutrients via fertilizers anyway. Finally it is also important to tailor the mix to the environment you grow the plants in, i.e. you have to factor in if your pots are clay or plastic, the climate you live in, your water regimen, etc.

I've heard it said that there are probably as many soil mixes as there are cacti growers. This post is the current take on my recipe for a cactus soil mix ;-)

The ingredients
Below you'll find the list of ingredients that I'm currently using for my cactus soil mix.

Unprocessed, raw moler
Unprocessed moler
Unprocessed moler

Moler is a naturally occurring mixture of diatomaceous earth (a soft, chalk-like sedimentary rock) and bentonite clay, approximately 60% diatoms and 40% clay. Moler is quarried not too far from where I live, so once in a while I swing by one of the defunct quarries that are open to the public and fill up the car ;-) Instead of moler you could use chunks of granite or whatever rock is available to you – the advantage of moler is that it is very lightweight, but it is probably not very easy to obtain outside of Denmark. These larger pieces of rock are added to keep the soil open and allow air to get to the roots, furthermore the rock will reduce the volume of water a given amount of soil can hold.

Sharp sand
Sharp sand
Sharp sand

Sharp or coarse sand (grit) should be readily available everywhere (otherwise ask your mason ;-). The sand reduces the soil's ability to retain water.

Limestone gravel
Limestone gravel
Limestone gravel

Many cacti, including Ariocarpus and peyote (Lophophora), are native to limestone areas, often growing within cracks in the limestone boulders themselves. For such species I'm adding a bit of limestone gravel to the soil mix – please note we are talking limestone and NOT lime which will scorch your plants. The limestone gravel also reduces the volume of water a given amount of soil can hold

Cat litter, baked moler
Cat litter, baked moler
Cat litter, baked moler

It almost goes without saying that the water absorbing and retaining qualities of this product are excellent ;-) Still, this type of cat litter don't feel soaked even when fully wet. To the best of my knowledge this product is widely available, but watch out for the scented variety – unless you want your plants to smell of cheap perfume ;-) If you can't find this type of cat litter you can try substituting it with crushed brick.

I once used small LECA pellets but stopped as they have a tendency to float on top of the soil and also they don't retain much water.

Cat litter, bentonite clay
Cat litter, betonite clay
Cat litter, bentonite clay

Another water absorbent. I read somewhere that peyote and Ariocarpus enjoy pellets of clay in their soil, so I decided to try adding some of these bentonite clay granules.

The clay granules do not dissolve when watered, i.e. the bottom of the pot will not clog up because of the clay pellets.

The mix
I recently repotted a handful of newly acquired Ariocarpus plants in the following mix:

  • 4 parts unprocessed moler
  • 3 parts sharp sand
  • 2 parts limestone gravel
  • 2 parts baked moler (cat litter)
  • 2 parts betonite clay (cat litter)
This is the same mix illustrated in the first photo of the post.

Coir
Coir
Coir

If you want your soil to hold more water you can add coir (a product made from coconut fibers). I used to add peat moss (sphagnum) but nowadays I prefer coir for several reasons. First of all completely dry coir is easy to wet while completely dry sphagnum moss seems to almost repel water. Also, peat moss is mined out of bogs, and takes years to renew. Avoiding peat and going for coir will make a bog somewhere very happy ;-)

What others say about soil mixes
Soil mixes were also recently discussed on the cacti_etc mailing list resulting in some interesting replies, like:
Now pretend that I also gave you 500 additional words explaining why this mix, or any other general mix, may or may not kill all of your plants. The appropriateness of any mix depends on so many things, like what plants you're growing, what kind of pots you use, the size of your pots, your local climate, whether or not you have a greenhouse or are a windowsill grower, your watering habits, etc.

And the slightly more humoristic approach:
Just keep in mind that, for succulents and cacti, you want a pot and soil mix that dries out in about 5-7 days after you water it. You can't control the humidity and temperature but you can control the soil mix, the size of the pot, whether the pot is clay or plastic, and how often you water. (Well, some people can control how often they water--others can't. Those are the same people who can't stop giving their dogs treats.)

If you are looking for general information on cactus growing the cacti_etc mailing list is a good place to go.

Sunday, March 15, 2009

Repotting Lophophora williamsii in the coldhouse

Since 2004 I have experimented with growing Lophophora williamsii in an unheated greenhouse in Denmark. During this period the plants have been repotted only once a couple of years ago.

Coldhouse grown Lophophora williamsii (SB 854; Starr Co, Texas)
Coldhouse grown Lophophora williamsii (SB 854; Starr Co, Texas)

The plants are growing in 11 cm (4.33'') clay pots and it might not be apparent from a superficial inspection that they are in need of being repotted again. But on closer investigation it turns out that the taproots are visible through the drainage hole in the bottom of the pots.

Taproot visible through drainage hole
Taproot visible through drainage hole

I consequently decided to repot the plants. I'm usually not repotting plants in the coldhouse this early in the year as we still might get the occasional night with sub-freezing temperatures, but I figured that the plants are completely dormant – i.e. there are no actively growing roots to harm – and if repotted in bone-dry soil the plants will not notice they have been disturbed when the growing season starts in a few weeks. Anyway, that's my theory ;-)

Lophophora williamsii plants removed from the pots
Lophophora williamsii plants removed from the pots

Close-up of three Lophophora williamsii crowns
Close-up of three Lophophora williamsii crowns

Close-up of exposed Lophophora williamsii taproot-ball
Close-up of exposed Lophophora williamsii taproot-ball

After removing the plants from their pots I could smell that some of the roots had been damaged; a broken Lophophora root gives off an easily detectable smell reminiscent (to me anyway ;-) of that of fresh green peas. This stressed the fact that the soil really had to be bone-dry before potting the plants, so I let them sit for a day in order for the broken roots to dry out a bit, and shoved the soil into the oven to remove every last bit of moisture it might hold (this gave off an... let's call it interesting... smell and I weren't popular at all with the rest of the house).

The soil ended up being so dry that I was literally working in a cloud of dust while repotting – my throat was still irritated the day after so I'll probably buy a dust mask to avoid this situation in the future (not that I expect to get pneumoconiosis or anything but it's annoying to go “ahem”, “hrmph”, “cough” for a day when it can be avoided ;-).

Freshly repotted Lophophora williamsii plants
Freshly repotted Lophophora williamsii plants

The dry and dusty soil is also evident by the dusted fingerprints on the pots (12 x 12 x 20 cm, ideal for plants with large taproots) in the picture above.

Lastly I would like to make a note on the soil. I am adding unperfumed (and unused ;-) cat litter made from baked “moler” to my soil as this material is very lightweight and retains water easily without the soil getting soaked. I'm not quite sure how to translate “moler” into English but it is a diatomite deposit that Skamol, a “moler” processing plant, defines as:

Moler - a diatomaceous earth
Diatomaceous earth is a naturally occurring, soft, chalk-like sedimentary rock that is easily crumbled into a fine white to off-white powder. This powder has an abrasive feel, similar to pumice powder, and is very light, due to its high porosity. Moler is a special mixture of diatomaceous earth and bentonite clay, ca. 60% diatoms and 40% clay. The clay gives the raw moler a brownish colour, and due to a high iron oxide content the materials become pink, when baked.

The pinkish granules visible in the topsoil in the photo above is “moler” cat litter.

As I live within driving distance of where the “moler” is quarried I decided to get some raw and unbaked “moler” to mix into my soil. Last summer I collected a few bags in the, now defunct, quarry pictured below; the plants described in this post are the first to be planted in soil with chunks of raw “moler” mixed in (visible as large, grayish flakes in the above picture), so I'm eager to see how the plants agree with this new additive to their soil. Even though “moler” contains large fractions of clay (the Danish word “ler” means clay, i.e. a literal translation of “moler” would be mo-clay) it's a relatively stable material that doesn't dissolve in water, so it will not clog up the soil when watered.

Old moler quarry on the island of Mors
Old moler quarry on the island of Mors

I'm a bit curious as to what effect diatomaceous earth has on insects. According to Wikipedia “diatomite is also used as an insecticide, due to its physico-sorptive properties. The fine powder absorbs lipids from the waxy outer layer of insects' exoskeletons, causing them to dehydrate”, i.e. the diatomaceous earth in the “moler” might actively help me control pests.

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