Are you growing your cacti in a soilless mix?

[Steve Johnson]

I actually do that with North American species, although not ones with tap roots. Sips every 4 weeks, but not if your overnight lows are in or below the 30s. If you keep your cacti indoors during fall and winter, you won't have a problem. No water at all for South American species.

How much do you consider a sip, Steve?

I'm still pretty gun-shy from last spring when I almost killed my Organ Pipe.

A sip means getting the mix a bit moist without accidentally drenching it. This is something you'll have to develop a feel for. With smaller pots, you can practice in the growing season like this:

• Spray bottles you buy at the nursery or online have 2 settings -- mist and stream. Set the bottle to stream.

• Squirt water evenly around the base of the plant. Make a note of how many times you "pull the trigger".

• If drops of water don't come out the drain hole, you have the right amount for the pot.

• If drops of water do come out the drain hole, you overdid it. Try again with fewer "pulls of the trigger" and determine the right amount for the pot.

Overdoing it is not a problem in the growing season because your cacti need deep watering anyway. The point is to do some trial-and-error practice while they're growing. If you keep a list of cacti that would enjoy sips in the fall and winter, and write down the number of "trigger pulls" for each cactus, you won't accidentally drench them. With bigger pots (1-gallon pots, for example), you'll have to use a watering can and be careful about it.

[ChaoticN]

I finally have everything in you recommended Steve and I also wanted to mention that since I incorporated the DG, my medium does go bone dry in about 5-7days but I’m wondering if it will be the same outside under the sun.

Now my question is, what’s the formula with the fertilizer mix? I do have a Blue labs EC meter and a really nice digital scale if needed.

[Steve Johnson]

I finally have everything in you recommended Steve and I also wanted to mention that since I incorporated the DG, my medium does go bone dry in about 5-7days but I’m wondering if it will be the same outside under the sun.

If your pots are nonporous (plastic or glazed ceramic/high-fired clay), wet-to-dry time will be the same under the sun. In case you didn't already see it, this is why I highly recommend nonporous pots:

viewtopic.php?t=45833

I also recommend gravel top dressing -- it adds a nice decorative touch, and it also keeps the upper layer of the mix from drying out too quickly.

Now my question is, what’s the formula with the fertilizer mix? I do have a Blue labs EC meter and a really nice digital scale if needed.

You'll definitely need the scale for this:

Stock solutions

For an ammonium sulfate-potassium sulfate stock solution, dilute 5.78 grams ammonium sulfate and 8.4 grams potassium sulfate per gallon of distilled or RO water (not tap or well water). If your container is translucent (like a milk jug or something similar), algae will have a feast in the stock solution if you keep it in the light all the time, so keep it in a dark place when you're not dispensing the stock solution.

For a sodium molybdate stock solution, dilute 0.18 gram per pint of distilled or RO water. Given the small collections you and I have, that pint might last us into the next lifetime!

Watering solution

The following dilutions are per gallon of water:

• 1/2 tsp. General Hydroponics FloraMicro

• 1/2 tsp. GH FloraBloom

• 6 fluid ounces ammonium sulfate-potassium sulfate stock solution

• 1/4 tsp. sodium molybdate stock solution

• 1/4 tsp. nitrogen-free TPS CalMag

Fill your watering container about 3/4 of the way up, then add the FloraMicro, stock solutions, and CalMag. Fill it up to the fill line, and add the FloraBloom (plus acidifier if you're acidifying tap water) last -- this step is required per General Hydroponics. Cap the container, shake well, and water away. I still need to post an updated "how-to" guide on acidification, so I should have it soon.

For the sake of being thorough, here are the watering solution's nutrient dosages in parts per million:

• Ammonium N = 17 ppm, nitrate N = 31 ppm, total N = 48 ppm

• P = 14 ppm

• K = 74 ppm

• Ca = 33 ppm

• Mg = 10 ppm

• S = 38 ppm

• Mo = 0.053 ppm

These dosages are pretty much perfect, and so is the NPK balance. The Ca and Mg you get from acidified tap water will be bonus.

One final note -- the watering solution has a very limited "shelf life". The algae problem I mentioned is more of a problem if you keep it for more than a day or two, so best if you use it up right away.

[ChaoticN]

Thank you for all ur help Steve & you as well Tom you guys have have definitely saved my cactus plants from dying on me with the knowledge you two shared.

You were not kidding when u said I wouldn’t need a pound of Sodium molydbate , 0.18 is a very minuscule amount.

I was wondering though do you think the pumice/DG mix is good enough for jungle cacti? Or succulents like stapeliads. I have a few aporocactus and a few celestocactus plants potted up in it & those I have been watering a little bit more than the rest but only with tap water ph’d to 6.0 with citric acid up until now.

[jerrytheplater]

I was wondering though do you think the pumice/DG mix is good enough for jungle cacti? Or succulents like stapeliads. I have a few aporocactus and a few celestocactus plants potted up in it & those I have been watering a little bit more than the rest but only with tap water ph’d to 6.0 with citric acid up until now.

I have my Christmas Cactus potted as if it were an orchid in Orchid bark of two sizes. I did that in the early summer of this year. Its blooming now.

Here is where I described it. Start at Oct 13. https://cactiguide.com/forum/viewtopic. ... 7&start=15

I do have one pot of Cleistocactus potted in a mineral mix with added peat moss, but I'm not final on what I'm going to do there. They have grown more than double since purchasing them last December. I'm seeing some Frailea seedlings really growing slowly in a mix with very little organic. I may have to repot them to see if they want more organics.

[Steve Johnson]

Correct -- for jungle cacti like Christmas cacti, Thanksgiving cacti, etc., I think Jerry is on the right track. While a straight pumice-granite gravel mix is great for most desert cacti, I'll point out a few exceptions:

• Opuntioids (Tephrocactus for example)

• Echinopsis

• Eriosyce senilis

These cacti do need soil in the mix, in which case I'll recommend a 50% soil-50% mineral gravel mix. The only succulent I grow is a Haworthia attenuata, and it's also in a 50% soil-50% mineral gravel mix. My experience with succulents in general is close to zero, so I don't know if their roots would support a soilless mix without organic material.

[ChaoticN]

Oh Steve or anyone who can answer this - I was kinda curious and sorry for asking so many questions but for certain verities that like limestone in the mix, could I replace the DG with it or would I do better with a combo of all 3 / Pumice,DG & limestone.

[Nino_G]

I was kinda curious and sorry for asking so many questions but for certain verities that like limestone in the mix, could I replace the DG with it or would I do better with a combo of all 3 / Pumice,DG & limestone.

Plants that grow in limestone in nature have adapted to it so they can tolerate such growing medium in order to avoid competition, it doesn't mean that they necessarily need it in cultivation. Of course, you may add limestone to your preferred substrate mixture, or you may even grow them in pure limestone, but please note that calcium carbonate acts as a growth retardant. Plants cultivated in such medium will resemble plants in the wild in shape and color more accurately , but will grow much, much slower.

[Steve Johnson]

Oh Steve or anyone who can answer this - I was kinda curious and sorry for asking so many questions but for certain verities that like limestone in the mix, could I replace the DG with it or would I do better with a combo of all 3 / Pumice,DG & limestone.

Our go-to guy on this is MikeInOz. Cacti which are native to limestone soils can absorb calcium in a slow-release manner, but limestone will inhibit growth in cacti which aren't. A little bit of limestone in the mix is fine for most North American species, not fine for South American species. All desert species can absorb Ca from gypsum. If one is inclined to go that route, use gypsum granules -- once again a slow-release form of Ca that lasts for months as opposed to weeks with gypsum powder. Ca and Mg in the fertilizer regimen I use are immediately available to the plant. This is also true of the Ca and Mg reaction products from acidified tap water. IMO these should be the primary sources for your cacti, but if you'd like to add gypsum as a small slow-release Ca bonus, you can go with Mike's recommendation -- 1 or 2 grams of gypsum granules to about 1 liter of mix as a top dressing. In fact, he said that it'll last you for the entire growing season.

[ChaoticN]

My main concern was the mediums ph, I was thinking species native to that kind of soil required a ph around the same of the limestone.

I got dolomite lime from DTE but I wasn’t sure about using it we’re it’s more of a powder consistency. Those granules might just do the trick though if all they need is extra calcium.

[Steve Johnson]

My main concern was the mediums ph, I was thinking species native to that kind of soil required a ph around the same of the limestone.

Cacti and other xeric plants growing in limestone soils are adapted to it, so alkaline pH is a matter of tolerance, not requirement. You'll be fine with the pH-neutral pumice-granite gravel mix.

I got dolomite lime from DTE but I wasn’t sure about using it we’re it’s more of a powder consistency. Those granules might just do the trick though if all they need is extra calcium.

You and I are giving our cacti plenty of calcium through the ferts and acidified tap water, so adding dolomite to the mix is purely optional.

[7george]

Hello everyone, I’ve recently went to a full hydro mix of pure pumice and it takes around 8-10 days to go from fully wet to bone dry depending on how warm and dry the environment is.
Should I add in another mineral that doesn’t hold as much moisture to get the medium to dry out faster or is that time frame acceptable for wet to dry.

It depends on your climate, growing conditions and watering habits, also plants grown. I usually add something to the mix that will increase water retention (vermiculite or sand), especially for smaller pots.

[ChaoticN]

Hey Steve I got this granular fertilizer in the other day & I wanted to see what u thought about its nutrition value, it says it’s made for cactus an succulents and the NPK looks similar to what me and you use.

I still plan on using what you recommend but this was cheap and I wanted to have a backup for some if I ever got to lazy to mix more than a gallon or 2.

[Steve Johnson]

Hey Steve I got this granular fertilizer in the other day & I wanted to see what u thought about its nutrition value, it says it’s made for cactus an succulents and the NPK looks similar to what me and you use.

I still plan on using what you recommend but this was cheap and I wanted to have a backup for some if I ever got to lazy to mix more than a gallon or 2.

Let's break it down -- 11-10-11. 10% P2O5 x 0.436 = 4.36% P. 11% K2O x 0.83 = 9.13% K, so the elemental NPK is actually 11-4.36-9.13. 4.36/11 = 0.4 on the P side of the NPK ratio -- too high. 9.13/11 = 0.83 on the K side of the ratio -- too low. Not thrilled about the lack of calcium in the fert either. Whenever we see ferts "made for cacti and succulents", all it tells us is that the manufacturers don't know anything about the optimal nutrient requirements for said cacti and succulents. You can use the 11-10-11 every once in awhile, but that's it. I personally wouldn't use it at all.

[Nino_G]

I found this article and it is very interesting:

https://geologybase.com/pumice/

Among other things it says:

"Pumice composition
Here is the chemical and mineral composition of pumice:

1. Chemical composition
Pumice is a frothy volcanic glass that forms mainly from highly viscous felsic or silicic to intermediate magmas like rhyolitic, andesitic, dacitic, trachytic, pantellerite, or phonolitic magmas and rarely from mafic magmas like basalt. For instance, Tenerife in the Canary Islands, has phonolitic pumices.

Thus, pumice composition will mainly be silica (SiO2) 55-77 wt.% and considerable amounts of aluminum oxide (Al2O3). Also, they have potassium oxide (K2O), sodium oxide (Na2O), calcium oxide CaO, magnesium oxide MgO, sulfur trioxide (SO3), and iron oxide (Fe2O3) in varying amounts depending on which magma it is.

However, if of mafic origin, then it will have a lower amount of silica, 45–52 wt.%, with more of the mafic elements like calcium, iron, and magnesium and less of the felsic constituents like sodium and potassium.

On the other hand, rhyolitic magmas, which are felsic, will tend to have more silica, sodium, and potassium and less of the mafic elements like calcium, iron, and magnesium. Intermediate magmas will have a composition in between mafic and felsic.

Going to specific examples, the chemical composition of pumice from El-Arish, North Sinai, Egypt, according to Ismail et al. (2014), is silicon dioxide 70.97%, titanium oxide 0.14%, aluminum 14.24%, iron oxide 1.88%, calcium oxide 1.37%, magnesium oxide 0.35%, potassium 4.46%, sodium 4.02% and others 2.41%. This example was probably rhyolitic, going by the higher amount of silica."

It seems to me that pumice is not mere hydropinic medium, but has quite a bit of nutrients too.