Are you growing your cacti in a soilless mix?

[Steve Johnson]

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.

8-10 days isn't bad, although based on my own experience, 6-7 days is better. The soilless mineral mix I use is 60% pumice/40% granite gravel, and the granite acts as a sort of "moderator" that keeps the pumice from taking longer than we'd like going from wet to bone dry. The humidity in my area (coastal L.A.), may be a little higher than yours, so I think a 70% pumice/30% granite gravel mix should be fine for you.

The only downside to a pure mineral mix is that you'll need to fertilize pretty much every time you water in the growing season. However, it's not much of a downside since this comes with the upside of excellent long-term growth in desert cacti. Give me the details on the fertilizer you're using, and we'll see if you have the right one.

[Nino_G]

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.

Hello ChaoticN,

drying time depends on many factors:
- size of your pots (smaller pots dry faster)
-shape of your pots (shallow pots with large surface area will dry faster than narrow, deep ones)
- granulation of the pumice used (small grain pumice generally retains more water and, hence, dry slower)
- some plants absorb more water than others, their pots will dry faster
- whether you are using top dressing or not (what type of top dressing, what depth)
- climate conditions

It's difficult to give answer to your question without taking into account all of the above. Also, I'm interested how did you measure "fully wet" (saturated) to "bone dry"? Do you water your plants overhead, or by soaking in a water dish?

Best regards,
Nino

[Steve Johnson]

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.

Hello ChaoticN,

drying time depends on many factors:
- size of your pots (smaller pots dry faster)
-shape of your pots (shallow pots with large surface area will dry faster than narrow, deep ones)
- granulation of the pumice used (small grain pumice generally retains more water and, hence, dry slower)
- some plants absorb more water than others, their pots will dry faster
- whether you are using top dressing or not (what type of top dressing, what depth)
- climate conditions

It's difficult to give answer to your question without taking into account all of the above. Also, I'm interested how did you measure "fully wet" (saturated) to "bone dry"? Do you water your plants overhead, or by soaking in a water dish?

Can't speak for ChaoticN, but I determined the time it takes for my pumice-granite gravel mix to go from saturated to completely bone dry by weighing a bunch of different pot sizes (and cacti in the pots of course) with a digital scale. I did that in spring 2013 writing down their dry weights, saturating the mix and writing down their wet weights, then weighing the pots every day until they were back at their dry weights. The results were surprising -- bone dry after 6-7 days regardless of pot size. I went through the exercise again that summer, and the results were even more surprising -- bone dry after 6-7 days in the heat of summer. Although I never developed the talent for it, some growers are able to weigh their pots by hand and tell if the potting medium is bone dry, so maybe ChaoticN is one of those growers.

[Tom in Tucson]

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.

Hello ChaoticN,

drying time depends on many factors:
- size of your pots (smaller pots dry faster)
-shape of your pots (shallow pots with large surface area will dry faster than narrow, deep ones)
- granulation of the pumice used (small grain pumice generally retains more water and, hence, dry slower)
- some plants absorb more water than others, their pots will dry faster
- whether you are using top dressing or not (what type of top dressing, what depth)
- climate conditions

It's difficult to give answer to your question without taking into account all of the above. Also, I'm interested how did you measure "fully wet" (saturated) to "bone dry"? Do you water your plants overhead, or by soaking in a water dish?

Can't speak for ChaoticN, but I determined the time it takes for my pumice-granite gravel mix to go from saturated to completely bone dry by weighing a bunch of different pot sizes (and cacti in the pots of course) with a digital scale. I did that in spring 2013 writing down their dry weights, saturating the mix and writing down their wet weights, then weighing the pots every day until they were back at their dry weights. The results were surprising -- bone dry after 6-7 days regardless of pot size. I went through the exercise again that summer, and the results were even more surprising -- bone dry after 6-7 days in the heat of summer. Although I never developed the talent for it, some growers are able to weigh their pots by hand and tell if the potting medium is bone dry, so maybe ChaoticN is one of those growers.

🖒

[ChaoticN]

You’ll probably laugh at me. The fertilizer I currently am using is GH Maxi bloom supplemented with blue planet cal mag. I also have a blue labs ppm/EC meter that I use for measurements an I use RO water but I never feed higher than 500ppm, usually it’s around 260ppm-300. I’ll post a pic of the nutrition values on the fertilizer packages.

When it comes to medium or rocks per sae, there are a few rock yards in the state I live in but unfortunately none carry pumice, lava rock, kyodama, crushed granite, Ect.. they do fortunately have limestone but anything else has to be ordered and that’s typically fine as Im okay with a little cost here an there and I want to slowly build my collection.

Currently I have 3/8” & 1/4” sized/screened pumice plus the fines, 1/4” & 3/5” sized black lava rocks and a very large bag of brown colored aquarium pebbles that are about 1/4” in size but they are the shiny kind that have been tumbled.

As for how I got my wet to dry measurements, I dip the pot into a reservoir of water till I see it has worked it’s way to the top layer through osmosis. I then waited a few days to see but I had to repot a few to determine when it got dry.

[Nino_G]

Well, I'm not sure what influence relatively long drying period in your case. My mineral mixes tend to dry within a week (similar to what Steve wrote). Do you keep your plants outside or indoor/greenhouse?
I guess your mixture will be ok for most cacti, except for extreme xerophiles who would probably be in some risk.

[ChaoticN]

There currently indoors for the winter till next year, I do have a 4x4 grow tent with a true 500w led though and another small 2.5x2.5 grow tent with a 150w led.

Plus a good shelf that get supplemental lighting from a 100w led and a little sunlight through my window.

Also the mix I use is currently 100% 1/4” sized pumice, I haven’t mixed any of the larger sized in yet. Waiting on Steve to check in an tell me if I should add in the lava rock or the other aquarium pebbles or just add the larger pumice in as well with the small stuff.

[Steve Johnson]

Hi ChaoticN,

A few things to unpack here...

First, go with crushed granite poultry grit instead of aquarium pebbles. You can buy it on Amazon, although maybe too expensive if you have a lot of plants. If that's the case, look for the possibility that you can buy crushed granite at a local nursery or feed & tack store selling poultry supplies.

Regarding fertilizers, see this:

viewtopic.php?t=47603

I realize there's a lot of detail in my presentation, but worth taking the time to read through it thoroughly. Regarding nutrient ppm numbers in your watering solution, nitrogen is the benchmark that tells us if we're overfeeding our cacti and succulents. 40-60 ppm N per feeding is good, between 60 and 90 ppm is okay. Anything above 90 ppm per feeding, and cacti end up with something called "nitrogen bloat". If the amount of N they get is within the optimal 40-60 ppm range, everything else falls into place if the P and K balances and dosages are right. You'll see this issue being discussed in my presentation.

I'm working with a member in Indonesia who needed help with his fertilizer, and part of the discussion dealt with the important role calcium plays in plant growth. I'll pull out something I said there -- a lesson learned from hydrobuilder.com:

• "Calcium has a similar role in plants as in humans, helping produce strong cells and root walls. This leads to stronger plants. We've recently come to understand that calcium is actually the dominant nutrient in most plants." [My emphasis]

This is certainly true for cacti and succulents, although we should know that magnesium is also important (but in smaller amounts). Believe it or not, the hardness in tap water can provide Ca and Mg to plants, but there's a problem -- Ca and Mg are "locked out" by carbonates in the water. Solution -- acidify. The 2 acidifiers safe for home use are 5% white vinegar and citric acid. For growers with big collections, citric acid is better than vinegar because it's more concentrated. The reaction products of acidification:

• Calcium acetate and magnesium acetate from vinegar.

• Calcium citrate and magnesium citrate from citric acid.

Acetates and citrates are highly soluble in water, so either one of these avenues makes Ca and Mg available for uptake by the roots of your plants. Back in 2019, I posted a "how to" guide on acidification, but the info is really outdated, so I'll put a new one together soon.

Getting back to the subject of fertilizers -- I became a huge fan of hydroponic ferts when I went soilless in 2012, and I highly recommend them because their nutrient profiles tend to be more comprehensive than what we'll get from dry water-soluble ferts. After Dyna-Gro discontinued the 7-7-7 I was using, I went over to General Hydroponics FloraMicro 5-0-1 and FloraBloom 0-5-4. Put 'em together, and we get 5-5-5. Only problem there, P is too high and K is too low in relation to N, so I struck the right balance with ammonium sulfate and potassium sulfate. Add in some nitrogen-free Cal-Mag from TPS to supplement the Ca and Mg my cacti are getting from acidified tap water. If you'd like to do the same, I'll be happy to give you the "recipe" and instructions. If you'd rather go with a different fert, look for one with equal NPK numbers (7-7-7, 10-10-10, etc.), and I can help you with the supplements that'll give you a well-balanced feeding regimen for your plants.

[ChaoticN]

Thank you Steve! I did not know the poultry grit was crushed granite, I definitely will order a bag or 2. As for fertilizer I think I do have the flora series’s GH nutrients but if not I will order them as well. And thank you as well Nino you have given me a few things to think about that will help!

My collection is not very big yet, but I do have a massive amount of seed I want to grow out. Right now I’d say I have about 50 cactus plants maybe a little bit more but I’ll post here again once I get all the supplies in.

[Steve Johnson]

I did not know the poultry grit was crushed granite, I definitely will order a bag or 2.

Actually, there are 2 kinds -- crushed granite and oyster shell. Make sure you're buying the crushed granite.

As for fertilizer I think I do have the flora series’s GH nutrients but if not I will order them as well.

Excellent! Before your cacti wake up from winter dormancy and start growing next spring, I'll give you the details on the following:

• Ammonium sulfate-potassium sulfate stock solution. This supplements the GH ferts to give you the proper NPK balance.

• The amounts of the ferts and stock solution which go into your watering solution.

• The amount of nitrogen-free TPS CalMag which goes into your watering solution.

About 2/3 of the N in the watering solution is nitrate, so another supplement I use is sodium molybdate -- that's another stock solution, and I'll include it in the details. The reason why we should:

viewtopic.php?p=404209#p404209

Thank you Steve!

My pleasure!

[ChaoticN]

I got the granite in Steve and it’s a very good amount for what I paid on Amazon. I believe it will do my whole collection plus some.

Just waiting of the GH flora fertilizer now, I found some sodium molybdate but I’m wondering if this is good enough and also what else I’ll needed.

[Steve Johnson]

For the sodium molybdate, you won't need nearly that much -- try this:

https://www.amazon.com/TrueNute-Sodium- ... 160&sr=8-1

I bought a 1-ounce packet back in March, and it'll last me for quite a long time. Good since you and I have small collections (I'm growing only 68 cacti in 12 square feet of growing space). When you get to the ammonium sulfate and potassium sulfate powders, the smallest quantity you'll find on Amazon is 1 pound. A pound of each would last me into the next lifetime, so I was able to buy them in smaller quantities on eBay. Only problem with eBay is that items come and go, so just do a keyword search for sellers who can provide them.

[ChaoticN]

I would have everything in today Steve but Amazon messed up one of my orders and sent me the flora gro instead of the bloom. I did get everything else and I got in contact with them but unfortunately I’ll have to wait till Monday for the replacement to get here.

I was wondering too. Would giving some of the cactus plants I have pure water hurt, there’s a few that I think need it; Not a real drink but maybe a sip?

[Steve Johnson]

Would giving some of the cactus plants I have pure water hurt, there’s a few that I think need it; Not a real drink but maybe a sip?

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.

[zpeckler]

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.