SpriteFish wrote: ↑Sat Oct 05, 2024 7:44 am
Loam (Compacts and absorbent, I would only add a little.)
If you add soil, I would suggest perhaps not much more than 10-15% and watch the results.
I believe with loam, they stopped using it due to compaction causing suffocation and other issues. I'm unsure if adding grit will stop compaction enough for loam to be suitable, I do know that Mike suggested only adding a little loam, so that's probably why.
In fact, I wonder if the reason many of your plants didn't do well in loam, is due to the same reasons it isn't used in container gardening! It seems obvious when writing it out, but it would phrase the issue you were having as the fault of container gardening with a high amount of loam, and not loam itself.
Correct. When I purchased the first major round of cacti that started my current collection in June 2011, the people at the California Cactus Center who also sold me their "custom" soil-heavy cactus mix recommended adding pumice --
but only for some species. Unfortunately it was bad advice which set me up with a couple of problems I didn't realize at the time:
- I have always watered my cacti from the top. Every time I watered them in 2011, I had to wait for the water to soak in, then do it again (and again) until I saw it coming out of the drain hole. Think it took 1 or 2 minutes (maybe longer in the bigger pots). That means poor drainage, and it was a red flag I failed to see.
- Even though compaction wasn't an issue at that point (or maybe it was right from the get-go), all the loam in the mix was slowly suffocating the roots.
When I unpotted my cacti for the move from the CCC mix to soilless pumice and granite gravel in spring 2012, I was shocked by how bad the roots were. In fact, a few of the plants lost their roots completely. With the soilless mix, water drains all the way through in a matter of seconds (instantly with my smallest pots) -- excellent drainage and wide-open aeration that make cactus roots thrive.
As I've said a number of times in the past, my Tephros were the only cacti that wouldn't grow in the pumice and granite gravel because their very thin scraggly roots wouldn't grow in a mix that's too open for them. They love growing in the 50% pumice-50% CCC soil mix, so I'll disagree with Mike's advice on adding just a little bit of loam. When I water the Tephros, water drains all the way through in about 20-30 seconds, and compaction has never been an issue for me. However, I believe the 50/50 mix may be suitable
only for Opuntioids (Opuntia, Puna, Tephrocactus, etc.). For any other cactus species we're growing, I'd say that Mike's advice for adding 15% loam to the mix is spot-on.
SpriteFish wrote: ↑Sat Oct 05, 2024 7:44 amWhen I saw Fern fibre, I thought it looked like a great substitute for coir. If we're lucky it won't have as many downsides as coir, and might make a great addition, though I'm not sure how I'd test to see if it does has the same downsides.
You'll have to do what the rest of us have done -- trial and error. If you add fern fibre to the mix, see how your plants behave over the course of a year or two. If they respond by growing well, you're set. If they don't, you'll have to try again with another mix. Quite frankly, I'd be surprised if fern fibre has any downsides unless you have too much of it in the mix. Which brings us to this...
SpriteFish wrote: ↑Sat Oct 05, 2024 7:44 amAs I theorized in a different topic (I don't remember where), coarse sand may make a great substitute texture wise. I believe with coarse sand I also have to use a small percentage due to suffocation concerns (like 20% or less?), although that may be wrong...
I believe it's recommended for plants that like moist environments though, so if I do use it I'll use very little and see if it dries out appropriately.
Yes, coarse sand is a good soil substitute -- 1 mm-2 mm grain sizes won't get compacted as loam will. Only problem is that coarse sand won't retain water, so I'll recommend a mix of 50% pumice (it holds more water than you might imagine), 35% coarse sand, and 15% tree fern fibre for some additional water retention. When your cacti and succulents are in their growing seasons, water released to the roots will dry out the mix.
How often you should water isn't something you have to leave up to chance, so rather than just guess, here's a scientific approach you can take...
Pot up a few of your cacti and succulents representing the various pot sizes you have in your collection. Make sure the mix is completely dry when you start the test. Using a digital scale, weigh them in their pots and write down the dry weight. Saturate the mix until water is coming out of the drain hole. When the pots stop dripping, write down the wet weight and the date when you started the test. Weigh them on a daily basis until they go back to their dry weight and write down the date. That ends the test, at which point you can figure out a good watering schedule. For example -- if the pots go from wet to dry in 7-10 days, water every 2 weeks. Cacti and succulents take an incredibly long time to die of dehydration, but killing them with kindness by watering too often is a common mistake inexperienced growers make. To avoid making it, here's a good watering rule I learned from a senior member back in 2012 -- when in doubt, don't.
I'll leave you with one final thought for the moment...
MikeInOz wrote: ↑Mon Aug 05, 2024 2:42 am...plants are adaptable things and can keep going even with sub-optimal conditions.
To which I say -- why make do with sub-optimal when we know how to grow our cacti and succulents under more optimal conditions? In my carefully-considered opinion, potting mixes coming with nutrients pre-loaded by the manufacturer lead to sub-optimal results. That's why I'd rather take the time to give you the ingredients for a comprehensive and properly balanced feed you'll give to your plants with the mix I have in mind for you.