Are you growing your cacti in a soilless mix?

[7george]

The hydroponic approach is appropriate to humid or very humid climates. If your local climate is on the dry or very dry end of the scale, such a mix will dry out too quickly in the pot -- that's when you'll need a soil substitute for better water retention as the soilless mix dries out like it would in a soil-based mix.

This is a real problem for my pot-grown plants so I add at least some vermiculite, sometimes zeolite or sand into my mixes. Don't know if you consider decomposed organics and peat as a soil but sometimes I add those as well. I don't add soil dug out from my garden or other natural sites as these can contain pests or deceases harmful to my plants.


Kind of inorganic mix.

[Steve Johnson]

Don't know if you consider decomposed organics and peat as a soil but sometimes I add those as well.

The word "soil" tends to get used rather loosely, so a couple of definitions come in handy:

• Loam in its pure form is a mineral soil, and this pyramid describes the different types:
  

  

  Soil_pyramid.jpg (43.93 KiB) Viewed 85567 times

  Sandy loam soil is an ideal component for soil-based cactus mixes. But unfortunately pure sandy loam doesn't exist in the real world, which brings us to...

• Loam plus organic materials = humus. This type of soil is what we get either online or at our local nurseries/garden centers. At least here in the US, there was a time when commercial potting soils were generally good. However, the quality of those soils have been going downhill over the last 5 years (maybe longer), and quite frankly I wouldn't trust even the commercial products currently being sold as "cactus soil". (Expert growers who make their own custom soils know how to do it right, but they're in the minority among hobbyists.)

To answer 7george's question, any sort of organic material without a loam component is not soil.

I don't add soil dug out from my garden or other natural sites as these can contain pests or deceases harmful to my plants.

Good call -- I wouldn't either. 3 things about your mix do concern me a bit, though:

• Sand -- if it's coarse builder's sand, no problem. If it's fine "playground" sand, the sand will settle down in the pot and get compacted over time. Given the choice between zeolite and sand, IMO zeolite is better.

• Decomposed organics -- compost? Not sure about that, but if it works for you, great. You many want to consider chipped redwood bark instead.

• Peat -- are you talking about sphagnum or the peat being dug from peat bogs? If it's sphagnum, good. If it's the dead plant material coming from bogs, not good for cacti.

For our members who would like to include sphagnum for a soilless mix, here's something that might be helpful:

viewtopic.php?p=398714#p398714

[7george]

Decomposed organics -- compost? Not sure about that, but if it works for you, great. You many want to consider chipped redwood bark instead.

Some of the commercial I buy contain that stuff. It works for forest and other tolerant cacti but may contain lot of nitrogen looking at the plants growth. Chipped redwood bark - where to get this? Haven't seen this in our stores. I have used large chunks of spruce bark (from dead trees) and this worked good in mixes for epiphytes.

[Steve Johnson]

Chipped redwood bark - where to get this?

The curator at the Huntington Botanical Gardens desert greenhouse uses this:

https://sequoiascape.com/products/bark-mulches/

I believe it's the Double Grind Bark. His mix is pumice plus the bark for better moisture retention. He grows all of his cacti and succulents in it -- given the fact that redwood bark has a low pH, I think he must be using a buffering agent to bring it up. Maybe something like this?

https://www.amazon.com/General-Hydropon ... r=1-6&th=1

I don't think you'll be able to get redwood bark in Canada, but I'm pretty sure that pine or fir bark would work just as well. Now that I think about it, shredded would probably be better than chipped, so you might want to look for shredded bark. This brings up an interesting question -- do cacti get nitrogen from tree bark? If they do, I can understand why it may be a problem for desert cacti that should be getting all of their N from a fertilizer. MikeInOz, if you see this post, you're the best one to answer.

[jerrytheplater]

Chipped redwood bark - where to get this?

This brings up an interesting question -- do cacti get nitrogen from tree bark? If they do, I can understand why it may be a problem for desert cacti that should be getting all of their N from a fertilizer. MikeInOz, if you see this post, you're the best one to answer.

I'll put in an answer while you wait for Mike. Your question is, do cacti in cultivation obtain any nitrogen from organic material in the potting mix they are growing in? Specifically, can they get it from tree bark?

I searched for a chemical analysis of bark, even though I already knew it contained lignin, which does not contain any nitrogen. I wanted to see if there is anything else in bark which might contain nitrogen. The one article I read analyzed barks from conifers like cedar, fir, and pine and deciduous trees like oak, alder, and beech. Here is the link to it. : https://bioresources.cnr.ncsu.edu/wp-co ... _12505.pdf

None of the compounds listed as found contain any nitrogen, all are carbon, oxygen, and hydrogen containing compounds like lignin, cellulose, and some sugars. So, no nitrogen can come directly from bark by leaching as the pot is watered.

The bark leachate could feed soil bacteria, if any are in the pot. This is a question I've had-do potted plant mixes develop a bacterial community as they are used over time? I have been fertilizing some of my plants with bacteria containing fertilizer in hopes of having a more bio-active potting mix.

If the bark were to decompose by bacterial or fungal action, the bacteria/fungi will need nitrogen themselves to eat/decompose the wood. (I had this happen to me while in High School. I put fresh wood chips in my vegetable garden in hopes of increasing the organic content of the soil. What ended up happening was a disaster for my growing season. The bacteria in the soil used the available nitrogen in the soil from my fertilizer to grow and eat the wood. The plants I wanted to grow didn't because they did not have enough nitrogen. I learned I should have added extra fertilizer wherever I used wood chips. I also learned that wood chips should be composted before using in a garden.)

Eventually, the bacteria will die and then release the nitrogen they contain to the soil for use by plant roots. The nitrogen gets there indirectly.

So, that is the answer I give. Hopefully Mike might have input as well.

[keith]

naw too much work but if you cant find a good soil its probably better than most commercial potting mixes.

[MikeInOz]

This brings up an interesting question -- do cacti get nitrogen from tree bark?

Bark is very low in N. It won't make much difference in that respect.

[MikeInOz]

The bark leachate could feed soil bacteria, if any are in the pot. This is a question I've had-do potted plant mixes develop a bacterial community as they are used over time? I have been fertilizing some of my plants with bacteria containing fertilizer in hopes of having a more bio-active potting mix.

Bacteria grow and increase in numbers in direct proportion to the N available so it's doesn't matter what is in the mix, if there is low N there will be low bacteria numbers. The bark or other organic material is the food for them but without N they can't use it.

[Steve Johnson]

This brings up an interesting question -- do cacti get nitrogen from tree bark?

Bark is very low in N. It won't make much difference in that respect.

Excellent -- thanks, Mike!

[Steve Johnson]

Okay, here's a follow-up question that could be useful for growers who'd like to change from a soil-based mix to a soilless mix...

Bacteria grow and increase in numbers in direct proportion to the N available so it's doesn't matter what is in the mix, if there is low N there will be low bacteria numbers. The bark or other organic material is the food for them but without N they can't no use it.

Speaking in terms of parts-per-million, I don't think cacti would be overfed as long as N is below 90 ppm when they're fertilized, and IMO the 40-60 ppm range is probably better in the long run assuming that growers aren't fertilizing too often. If they aren't, they stick with the 40-60 ppm range per feeding, and they're using organic materials to replace soil as the component for moisture retention, is the fert feeding cacti or bacteria? If a lot of the N goes to the cacti and little bit goes to the bacteria, no problem. But if the bacteria get more than a little N, I can see a good argument in favor of upping the N closer to 90 ppm (maybe even higher?). What are your thoughts on this?

[MikeInOz]

, is the fert feeding cacti or bacteria? If a lot of the N goes to the cacti and little bit goes to the bacteria, no problem. But if the bacteria get more than a little N, I can see a good argument in favor of upping the N closer to 90 ppm (maybe even higher?). What are your thoughts on this?

Bacteria always win in the fight for N. ( ie: if there is not enough N in an organic mix the plant will starve first.) So there needs to be enough for bacteria plus plant. There is a scientific way to figure this out (nitrogen drawdown) but that is not necessary if there is only a small percentage of organic in the mix and some N is supplied continuously in some way. Because cacti are such slow growing plants they don't need much to get them by but they still need ''enough''. 40-60ppm every second or third watering is plenty!

[Steve Johnson]

Bacteria always win in the fight for N. ( ie: if there is not enough N in an organic mix the plant will starve first.) So there needs to be enough for bacteria plus plant. There is a scientific way to figure this out (nitrogen drawdown) but that is not necessary if there is only a small percentage of organic in the mix and some N is supplied continuously in some way. Because cacti are such slow growing plants they don't need much to get them by but they still need ''enough''. 40-60ppm every second or third watering is plenty!

Ah, this is good information! "Small" is a relative term, so it would be useful to quantify the proportions of organic and inorganic materials that work in soilless mixes. We have an excellent "go-to" person on this matter. John Trager has been the curator at the Huntington's desert collection for over 20 years -- wizard of a grower, and I've been in email contact with him before. I'll email him and ask about the proportions of the pumice and redwood bark mix he uses. If he changed the mix, he can give me the details. While I'm at it, I'll ask him about his fertilizer, how much goes into his watering solution, and how often he fertilizes. The Huntington is in Pasadena, and since it's more of a Mediterranean desert type climate (compared to the coastal climate in my part of L.A.), the experience John can relay will come in handy for growers living in rather arid conditions. I'll pass it along when I get the relevant info.

[Steve Johnson]

By the way, does anyone think this thread rates as a sticky? If so, I'll sticky it.

[Steve Johnson]

This just in...

I went through my emails with Mr. Trager at the Huntington, and I found out that he uses an 80% pumice/20% compost mix. Furthermore, here's what he said:

• "We use a product called 'Forest Humus' produced in the Sierra foothills from composted fir bark and maybe redwood. Their precise formula is proprietary but we have had good results with it compared with a few other products we have tried."

Unfortunately I don't think our members will be able to buy the product he gets, but Amazon may worth investigating:

https://www.amazon.com/s?k=composted+fi ... 1_0_recent

For those of you who can't go full hydroponic because you live in an arid climate, a simple 80% pumice/20% composted fir bark mix should work. And it's a soilless mix because there's no dirt involved. Mike -- are those percentages good, or do you recommend going a little lighter on the composted bark?

[jerrytheplater]

The bark leachate could feed soil bacteria, if any are in the pot. This is a question I've had-do potted plant mixes develop a bacterial community as they are used over time? I have been fertilizing some of my plants with bacteria containing fertilizer in hopes of having a more bio-active potting mix.

Bacteria grow and increase in numbers in direct proportion to the N available so it's doesn't matter what is in the mix, if there is low N there will be low bacteria numbers. The bark or other organic material is the food for them but without N they can't use it.

So, are you saying we have soil bacteria in our pots? (Obviously, you have no idea what every pot contains-Not asking that) Is there active decomposition going on in plant pots? Is it anything we should keep in mind regarding fertilizer application?

Will organic fertilizer mixes containing say, Hoof and Horn Meal, or Feather Meal, or Cottonseed Meal... (products that don't have much or any soluble Nitrogen, all insoluble) would they be of any benefit for a plant that will be in a pot for 2-4 years.