Are you growing your cacti in a soilless mix?

[ChaoticN]

The raised bed mix from my area only has decomposed leaf an wood chip according to the ingredients labeling on the bag. It could be a locality thing.

I’ll post a pic here in a bit for you, I work in a garden center but it could take me a little bit were I have to resize the photo to be allowed on here.

[ChaoticN]

This is the all purpose mix, I’m not sure about what there selling now cause the ingredients may have changed.

[Steve Johnson]

The raised bed mix from my area only has decomposed leaf an wood chip according to the ingredients labeling on the bag. It could be a locality thing.

I’ll post a pic here in a bit for you, I work in a garden center but it could take me a little bit were I have to resize the photo to be allowed on here.

Just saw your photo, and something jumped out at me...

In the quest for a soilless mix with organic material, shredded or finely chipped pine/fir bark holds out a lot of promise as the one and only organic component to use. John Trager of the Huntington Botanical Garden's desert greenhouse used a a well-composted pine and fir bark medium. But as he said, "It worked well enough but became quite hydrophobic when dry." Your Back to the Roots product includes yucca extract as a wetting agent. While I wouldn't recommend Back to the Roots, I think shredded or finely chipped bark plus yucca extract may be worth trying. Check this out:

https://www.amazon.com/Extract-Organic- ... 5533&psc=1

The idea here is to keep it simple -- one ingredient on the mineral side and one ingredient on the organic side. If yucca extract is effective as a wetting agent, give pine or fir bark a shot and you'll have the right organic to go with your mineral.

[ChaoticN]

I haven’t had that problem so far but I am adding in quite a bit of 1/8” akadama and 1/4” pumice. The mix feels like it”s about 35% worm castings 40% fully decomposed leaf matter and about 10% wood fines and like 15% orchid bark.

[AirWreck]

TBH, I'm hesitant to use anything conifer related for an organic component because exposure to pine needles falling from a pine tree overhanging my apartment balcony is what initially infected my collection with rust fungus. I lost half my plants from that event, including all of my Ariocarpus. Its been 20 years on now and I'm still grappling with rust fungus though it is on the wane. Cedars are a known host for rust fungus. That's why, for example, you can't have cedars near your apple trees. Last thing I want to do is inoculate my soil mix with rust fungus spores. I don't want this to happen to someone else. Assess your conifer derived product well before using it is what I recommend as some people find no problems with using it. I wouldn't trust anything in my area. So, I need something else if anything organic is to be used. On that note, please read the next paragraphs below.

If a "well composted" something is recommended, then why not worm castings or mushroom compost? Currently, I'm trying out worm castings. I'm assuming they offer active and balanced microbiota. My concern with worm castings or mushroom compost is longevity. How long will it be a contributing ingredient in the soil mix after potting up? Does it break down and wash away in a couple months or does it continue to contribute for a couple years? I know of a Thai cactus grower who personally composts leaves from a certain tree in his country and that is the sole organic component of his soil mix. Do a search for "Mr. Baso" on youtube. His plants are stunning! Some of the videos have English subtitles. I learned a lot about root trimming as a prevention for root rot from his videos.

Or as the thread title suggests "soilless mix" thereby indicating "none of the above" organic materials? I'm totally down for soilless, or perhaps better said organicless, if I can learn how to make it work on the long term using materials available to me. My current materials on hand are expanded slate, pumice, lava rock, turface and coarse sharp sand for the structural component of my soil mix. Fertlizer, trace minerals, and acidified water are the nutrient components for the nutritional regimen of my plants. I'm currently working all this out as I am currently redeveloping how I'm caring for my cactus plants. So, I really can't say much more as its still rather up in the air.

[ChaoticN]

If you can go pure mineral that’s what I would do, the organic bit is really only for certain species, mainly jungle types.

[Steve Johnson]

This is my 60% pumice-40% granite gravel mix:

Pumice-DG_rinsed04242016_forum.jpg (201.76 KiB) Viewed 422 times

Grain sizes range from 1 mm to 5 mm. The mix provides wide-open aeration to the roots, and cactus roots thrive in it. Not the best for growers living in arid climates, although they may be able to do well with nothing but pumice -- any members out there having success with that?

I'm now of the opinion that completely inorganic soilless mixes are the best way to go for this reason:

• Coarse organic materials (like tree bark and sphagnum peat) eventually break down and turn into slush, inviting pathogens to come in and have fun at your and your plants' expense.

Only way to avoid the problem is by repotting with fresh mix every 3 years or so. Call me lazy, but I'm in favor of repotting cacti only when they outgrow their pots and need a bigger pot. Speaking from personal experience, that's a nice problem to have! As I've mentioned in earlier posts, the only downside with pure mineral mixes is that cacti need to be fertilized every time they're watered in the growing season. But worth the effort when you enjoy seeing healthy well-grown cacti year after year. With that said, some cactus species do need to have soil in the mix. 2 genera which apply are Echinopsis and Trichocereus, so be sure that you know which cacti are or aren't suited to growing in a pure soilless mineral mix.

[SpriteFish]

What's the ideal grain size for pumice and gravel in this mix (Also does this change in a mix with soil)? I see that yours is between 1mm-5mm but are there any drawbacks to using slightly larger sizes (e.g. 5mm - 10mm grains)?

[Steve Johnson]

I see that yours is between 1mm-5mm but are there any drawbacks to using slightly larger sizes (e.g. 5mm - 10mm grains)?

5 mm-10 mm is quite a bit larger -- too open for a soilless mix. I grow 4 of my cacti in a 50% pumice/50% soil mix, so I'd recommend pumice with 3 mm-5 mm grains. It also depends on the size of the plant. If you have cacti in really big pots, you might be able to go with 5 mm-10 mm pumice in a pumice and soil mix. IMO 1 mm-5 mm is ideal for pure mineral soilless mixes regardless of pot size.

[Steve Johnson]

I'll have to correct myself on something I said:

• Coarse organic materials (like tree bark and sphagnum peat) eventually break down and turn into slush, inviting pathogens to come in and have fun at your and your plants' expense.

Here's the correction:

Organic material does NOT cause disease of any kind. Pathogenic organisms do. Pathogens do not ''come with'' organic material. They are everywhere including the computer screen you are looking at right now, all over your clothes and even in the dust in the air. All they need is food and the correct environment...So what is the problem with organic? Well it breaks down and as it does, water holding capacity goes up and air-filled porosity goes down. That can benefit some (but not all) pathogens. It is the same as using very fine mineral components to the mix. Therefore, using organic materials will be more acceptable for... plants which can tolerate slower drying in the mix (eventually), small pots, watering frequency which is low. Organic materials will be less acceptable for plants which do not like slowly increasing water holding capacity, large pots and watering frequency which is high.

AirWreck posted a couple of good points, and they're worth repeating:

Cedars are a known host for rust fungus. That's why, for example, you can't have cedars near your apple trees...Assess your conifer derived product well before using it is what I recommend as some people find no problems with using it. I wouldn't trust anything in my area...as the thread title suggests "soilless mix" thereby indicating "none of the above" organic materials?

The first point is really important, although composted pine and fir bark have been known to work well as the organic component for a number of growers. John Trager of the Huntington Botanical Garden's desert greenhouse used a mix of 80% pumice and 20% of that compost -- worked well until he found out that it became hydrophobic after repeated wet-dry cycles. Unfortunately he didn't investigate wetting agents, so I wanted to investigate this myself -- not for me, but for growers who might want to try something like what Mr. Trager did. Let's ask our cactus horticulturalist-in-residence:

New Zealand is where Orchiata bark comes from. They have a seedling grade (called ''Precision'') which is 3-6 mm. You can use that...

Only problem with any sort of tree bark is that it becomes hydrophobic after repeated wet-dry cycles. A wetting agent takes care of the problem, and I've read that yucca extract is a good one. We can find it here in the US, but I don't know about Australia and New Zealand. If yucca extract for plants isn't available there, would you recommend other wetting agents that'll work for growing cacti and succulents?

Yes. I use a commercial wetting agent. It's lasts the entire growing season. I would not recommend any of the organic types. Many have been found to not last long and to actually make things worse in some cases. I use it every year on many plants but still have not used it on cacti but I did notice some plants which were not potted for a while had difficulty absorbing water so next season I will try it out. It's important not to use too much and only do it once.
I use this. https://www.bunnings.com.au/amgrow-1l-w ... t_p3010119
I am sure there are similar products in the US

I'll leave this line of inquiry up to those of you who'd like to investigate further.

AirWreck's 2nd point gave me an idea on how we can more accurately describe different types of soilless mix:

• Organic soilless -- mineral gravel and coarse organic material. I'm pretty sure that we're talking about composts (maybe a loose definition?) which eventually break down into soil, and this is where the 1st quote from Mike comes into play. Compared to soil-based mixes, I think it'll take longer for the breakdown to get bad enough that water-holding capacity is unacceptably long. How long will depend on what growers experience, and the tricky part is knowing when they have to repot cacti with fresh mix. I can't see any way around having to go through some trial-and-error on this one.

• Inorganic soilless -- pure mineral gravel. Not only are its benefits significant, this is a low-maintenance mix because the gravels last forever. (Slight exaggeration, but pumice and calcined clay granules take a really long time to break down.)

Whether soilless mixes can or can't be used will depend on the species, so I'll break this down into 2 basic habitat types:

• Cacti native to North American and South American deserts -- soilless mixes. The only exception I can find involves cacti with very thin fibrous roots, and the Tephros I grow are examples -- they need a 50% pumice/50% soil mix.

• Cacti native to grasslands -- these species need a substantial amount of organic material, and their roots won't grow well in soilless mixes.

The 2 genera I mentioned in a previous post are Echinopsis and Trichocereus, both are native to grassland habitats, so what should we do about finding a suitable soil? I used to think that a lot of commercial potting soils are garbage because they're way too rich in organic materials for cacti. Mike corrected me (and by extension our other members) on the matter, hence my reason for posting his 1st quote -- maybe commercial potting soils aren't so bad after all. In fact, our US members might have just the right stuff:

https://www.amazon.com/Rosy-Soil-Cactus ... hdGY&psc=1

My default recommendation for soil-based mixes is 50% mineral gravel and 50% soil. Even though I don't have any experience with Echinopsis or Trichocereus, it's possible that you can tilt the mix more in favor of soil with a 40/60 mineral gravel and soil mix if you grow them. Based on what I saw with the ingredients listed, Rosy Soil holds a lot of promise. If any of our members decide to try it, I'd like to hear about their experiences good or bad after they've been using it for awhile.

[AirWreck]

I'm totally down for standardizing terminology- helps to reduce confusion. However, its too early in the morning for me to offer any suggestions.

Imo, soil is whatever you are putting into the pot whether mineral or organic, or a mix of the two- that's your "potting soil". And we should be clear that, by saying "organic", we are using that term in the chemical sense that the material is carbon based. We are not using it in the sense of organic agricultural processes.

We have a saying around here about the agricultural quality of one's soil. That is: "Don't let your soil turn into dirt." That is because soil will grow plants; dirt won't.