How do you know when they're thirsty?

[Maxy24]

So I'm asking this extremely newbie/basic question because I'm terrified of watering my cacti. Last summer I probably watered them three or four times and each time a couple of weeks later, I'd have a rotten cactus. I was told on here I must be watering them when they are not thirsty. So pretty much now when I water I am nervous for weeks because I'm waiting for one to die. I don't really know what I'm doing that's killing them. They're not terribly healthy, don't really grow (probably because I barely water them) and have small root systems. They've all been repotted this summer, last summer they were in pure pumice but it didn't appear to be doing them any favors so now they have some potting soil mixed in. So how do you guys decide that your cacti need water? Wait until they start to shrivel? Just wait until the substrate is dry? They've been over a month now without water and I feel like it's about time they get some, but how do I know if they actually need it?

[Steve Johnson]

So I'm asking this extremely newbie/basic question because I'm terrified of watering my cacti. Last summer I probably watered them three or four times and each time a couple of weeks later, I'd have a rotten cactus. I was told on here I must be watering them when they are not thirsty. So pretty much now when I water I am nervous for weeks because I'm waiting for one to die. I don't really know what I'm doing that's killing them. They're not terribly healthy, don't really grow (probably because I barely water them) and have small root systems. They've all been repotted this summer, last summer they were in pure pumice but it didn't appear to be doing them any favors so now they have some potting soil mixed in. So how do you guys decide that your cacti need water? Wait until they start to shrivel? Just wait until the substrate is dry? They've been over a month now without water and I feel like it's about time they get some, but how do I know if they actually need it?

There are quite a few things we need to go through here. I'll try to help you as much as I can...

1. Let's start with your potting medium. I've been growing cacti successfully in a pumice/decomposed granite mix. I could do it with straight pumice, so my only reason for the DG is to make the pots heavy enough to keep them from tipping over in the wind. There's no reason why you can't grow your cacti in straight pumice, although I went back to review some of your previous posts, and I think the pumice you were getting had too many big chunks. Bear in mind that pumice comes in different grades, so what you should look for is a grade with smaller grain sizes. Forget Amazon --this source from eBay should work out much better for you:

http://www.ebay.com/itm/3-5-GAL-HORTICU ... 4ac8424206" onclick="window.open(this.href);return false;

The 1/16"-3/8" grain size range is great, but you may want to pick out the biggest pieces and toss them -- don't think it would be all that labor-intensive. If this is the grade you've been using all along, then the pure pumice isn't your problem. While there are reasons for adding soil to the mix with some cacti, we can discuss this later.

Points 2, 3, and 4 should be considered as standard practice:

2. Whenever you transplant cacti, the roots need to be thoroughly cleaned to get any remnants of the old mix out. That includes digging up into the upper part of the root ball right below the base. It helps to periodically dunk the roots in a container of water as you gently dig through with something like a q-tip handle, knitting needle, etc. (I use the tip of a plastic ball point pen cap.) Beginners are always afraid of tearing off roots in the process, but this is no problem at all -- cacti know how to make more! Now here's a tip you probably haven't heard before. After you've gotten the roots squeaky-clean, soak them in 1% Hydrogen peroxide for 15 minutes. This kills any potential pathogens that could be hiding in there, and it also promotes faster healing of torn-off roots. After the peroxide treatment, rinse the roots gently, but thoroughly in running water, then let them dry out. And finally, repot the plant in fresh, dry mix. Let it settle in for 2 weeks, then you can start watering. If cacti keep rotting on you, now you know why and what to do about it.

3. Cacti need to be fertilized periodically. If you haven't been fertilizing yours at all, there's another good reason why your plants aren't growing. How often depends on the type of mix. When cacti are grown in a pure mineral mix, they need to be fertilized every time they're watered. Sounds like it might be kind of a pain, but I found it surprisingly easy to include this in my watering regimen. Once again, we can discuss this later.

4. Calcium bicarbonate in hard water slowly robs all plants of their ability to take up water and nutrients over time. Rainwater is best, although not an option for many. If you're in the same boat as the most of us, you'll have to water your cacti with the hard water coming out of your tap. Such being the case, acidification is the only way to go. 5% white vinegar is perfectly safe for home use. Dilution depends on the hard water's pH. Ferts will lower the pH some, and we have to factor that in for the amount of vinegar we should add. My water has a pH of about 8, so that's pretty hard. My fert is Dyna Gro All-Pro 7-7-7 liquid diluted at 1/2 tsp. per gallon of water, and I add 1 tbsp. vinegar. I also use a Milwaukee Instruments PH 600 meter, so I can tell you that the final pH of my fert/watering solution is 5.3. We don't have to be all that precise about it, so a pH in the 5.0-6.0 range is what we're looking for in good, healthy cactus growth. I started growing cacti when I was 12 in 1970, and I spent 21 years having problems that wouldn't be unfamiliar to you. After I had to be away from the hobby over the next 20 years, I was able to start a new collection 3 years ago. New collection, same old problems -- but I can't tell you how wonderful it was to see the turnaround with my cacti once I started following the practices in early 2012 which I'm describing here.

I know you were originally asking about how often you should water your cacti. IMO this was effectively putting the cart before the horse, since you're dealing with some serious problems in your basic growing approach that need to be addressed. I also know that I'm throwing a lot of info at you, but hopefully it'll put you on a better path. Please don't hesitate to ask more questions, and you have a good group here on the forum to help you out.

[greenknight]

I agree with all of that - except don't throw away the big pieces of pumice, you can easily crush them up into smaller pieces. The prices they charge for it, you'd be crazy to throw it away.

[Maxy24]

Thank you for such a well thought out response!

Yes the pumice I bought has a range of sizes, some are very large chunks and some are very small. What is the disadvantage to the larger pieces? Do you think I should repot again and use smaller pumice or will the pumice/potting soil be okay?

I did very thoroughly rinse all the soil from the roots before transplanting, I worried it might be damaging them too much (as roots were torn off) but I knew if I left the soil clinging to the roots they would stay too wet. I did not do any peroxide though, so perhaps that is where my problems began. This summer I was just going from pure pumice to the pumice/potting mix mixture so didn't have to damage any roots in the process. Maybe that's why I have not had any rot yet. Unfortunately I did just transplant two from soil a few days ago, so I'll have to be careful with them. I did always transplant into dry substrate and wait a couple of weeks to water.


I have fertilized, though it wasn't every watering, but I think I've been underwatering so badly they weren't really getting what they needed. This summer for example, I watered the cacti once in May, once in June, and once in July. Two of my cacti died over the winter because I thought I wasn't supposed to water them and they dried up (I had them in a closet so didn't notice they were dying). One of the cacti was also super shriveled but still looked alive. However after watering the cactus those three times it was still shriveled and flat. So I started to worry it was a goner and figured I might as well drench it. So instead of quickly pouring some water into the top of the pot until some came out of the bottom to let the pot sit in a container of water and let the all of the substrate get really wet all the way through. A few days later and the cactus is nice and plump again. I of course am still waiting to see if it'll rot. So obviously my previous waterings were not really getting the job done, which is why I feel like I should water everyone again by soaking.


I have a fish tank so from water testing for that I know we do have rather basic, hard water. I collect rain water for one my orchids so I can start doing that for the cacti as well, I didn't know they preferred acidic water.

I have one cactus that I'm really worried about, it was a gift and the person it's from is very sentimental, she'll be bummed if I kill it. There were actually three of them together in a container but two rotted last summer (one before I even watered it). I just feel like I should be doing something for it, but watering is the only thing I can think of and I'm terrified that it'll just rot.

[Steve Johnson]

Thank you for such a well thought out response!

Yes the pumice I bought has a range of sizes, some are very large chunks and some are very small. What is the disadvantage to the larger pieces? Do you think I should repot again and use smaller pumice or will the pumice/potting soil be okay?

Always happy to help whenever I can! When you're trying to grow cacti in straight pumice, the problem with an overly coarse aggregate is that you'll end up with a lot of air spaces which the roots won't want to grow in. Here's an example of the pumice I use:



From Amazon:



While this pumice may be okay for a mineral/soil mix, the grain sizes are way too big to use straight. If the pumice you have is pretty close to mine, then what you may want to do (based on greenknight's good idea) is separate out the big pieces, crush them down some, and mix them back in with the rest of your pumice aggregate. However, I'll go back to the grade of pumice I recommended in my eBay link -- if it looks like you'd have to do a lot of crushing with the pumice you purchased, then what you got was too coarse. The grade from eBay should be way better, and certainly less labor-intensive with the crushing you may want to do. And sift out the really fine stuff with a piece of fiberglass window screen.

Of course another option for you would be to stick with adding soil to your mix. But here's another problem for you to consider. Commercial potting soils are very rich in organic materials, and too rich for desert cacti. Sandy loam with minimal organics would be ideal, but something that's almost impossible to find here in the US. A huge advantage to growing cacti in pure pumice is the fact that it dramatically reduces the possibility of root rot. The only reason for adding soil to the mix is when we're growing cacti with very fine roots systems that can't be supported in coarse aggregates. A good example is Tephrocactus -- while the vast majority of my cacti grow remarkably well in a coarse pumice/DG aggregate, my Tephros languished for a year or more before I discovered that they need to have soil in the mix. After I moved them into a 50/50 mineral/soil mix, their roots really took off, and they've been pushing out new stems at a steady rate over the last year. If you really feel that you should be growing your cacti in a pumice/soil mix, then clean as much of the organic crap out of your soil as you can, and lean out the mix. I used 50/50 only for my Tephros, but you could tilt the ratio more in favor of pumice for the cacti you're growing.

I did very thoroughly rinse all the soil from the roots before transplanting, I worried it might be damaging them too much (as roots were torn off) but I knew if I left the soil clinging to the roots they would stay too wet. I did not do any peroxide though, so perhaps that is where my problems began. This summer I was just going from pure pumice to the pumice/potting mix mixture so didn't have to damage any roots in the process. Maybe that's why I have not had any rot yet. Unfortunately I did just transplant two from soil a few days ago, so I'll have to be careful with them. I did always transplant into dry substrate and wait a couple of weeks to water.

IMO you haven't gone far enough to prep the roots of your cacti before you repot them. Even with the cacti you had in pure pumice, there were still remnants of old soil somewhere in the roots. Follow my recommendations in point #2. Another example for you -- I got a Gymnocalycium baldianum from a local nursery last summer. While the plant was growing fine, the nursery's cactus mix was pretty horrible. Took a long time to dig it out of the root ball, and a fair amount of the roots got torn off in the process. Experienced growers will tell you it's nothing to be afraid of. This is what squeaky-clean roots look like after they're prepped and ready for repotting:



I'd like to discuss your watering approach further, but I'm running out of time for the night, so we'll pick this up again tomorrow evening. While we're at it, we can talk about pot materials and sizes too.

[greenknight]

Another thing - use small pots for plants with weak root systems, without much more space than the current roots occupy. I've seen cacti that weren't growing at all take off and do well when they were potted down into a smaller pot.

[Maxy24]

I really do think I cleaned them to the point you have in that picture, at least most of them. BUT greenknight bring up a good point, they are pretty much all over-potted. I went to home depot to get almost all of my pots and well, their selection stunk. A couple are just in pots I had lying around though. The only cactus in an appropriate sized pot is #9 below, though I think if the Cereus was in anything smaller it would knock the pot over. I tried to make up for it with false bottoms (filled it with rocks until I got to the size the pot should be) but I've read on here people think that's a bad idea, so I don't know if it's helping or hurting.

This is my pumice



This is what the soil/pumice mix looks like (each time I made it it was a little different, I wasn't measuring)



These are my cacti, I have IDs on some (that people on here told me). I don't know if their IDs will change their care at all.
1. Cereus peruvianus monstrose (skewers are to keep it from leaning over)


2. Not actually a cactus, they said a Euphorbia of some sort


3. No clue, this is one of the new ones I just repotted


4. I had the ID for this on the pot it came in but I lost it


5. No idea, this is the other new one


6. Stetsonia coryne


7. This is supposed to be a Saguaro, it's the one that was a gift


8. Old man of the Andes (not sure of scientific name...I know there are a few that claim that common name).


9. Some type of ferocactus. This is the one that was all shriveled up until a few days ago.


10. Totally forgot to take a picture of my last cactus, it's the one in the background of the toothpick cactus picture. It's also a ferocactus of some sort.



And the whole group

[Steve Johnson]

Unfortunately I won't have the time for going through everything I'd like to cover tonight. Since there's the weekend coming up, I'll have plenty of time to gather my thoughts and pick up where we left off tomorrow night. Until then...

#4 -- can't give you the ID, but the thin, stretched-out look of the new growth on top indicates that the plant isn't getting enough sun.

#5 -- Mammillaria spinossissima. Should be globular, but yours looks more columnar than I would expect. Not enough sun?

#8 -- "Old man of the Andes" is Oreocereus, either celsianus or trollii. New growth also looks etoliated. They'll take as much full sun as they can get.

Good discussion, and I hope this is helping you -- we'll talk again tomorrow night!

[Steve Johnson]

Okay, I'm back...

Your pumice actually looks pretty good. The only thing you'd really need to do here is crush down the biggest pieces as greenknight and I have recommended. After you do the crushing, just remember to sift out the really fine stuff with a piece of fiberglass window screen (my follow-up suggestion). I don't think you'll lose much, and the usable coarse aggregate you end up with should be great. I know you've had a disappointing experience with growing cacti in pure pumice, but it would be a shame if you give up on the idea. However, I totally understand if you don't feel confident about trying again. I don't know the ingredients in your potting soil -- from what I was able to see, it doesn't seem to be too heavily composted with organic materials, although looks can be deceiving. Twigs and bark? You can extract a decent amount of it out, and it's worth taking the time to do so. Peat? Avoid any commercial potting soil with peat, horrible stuff for a cactus mix. If your potting soil doesn't contain any peat, and you decide to go with a pumice/soil mix, just lean it out more. (Your mix does look too soil-heavy.) The more I think about it, the more I'm inclined to recommend a pumice-to-soil ratio of about 70/30. As with the pH of acidified water, we don't have to be all that precise about it. With that said, you should measure out your ingredients. Trying to ladle them out purely by hand means that you may "overdose" your cacti with too much soil in the mix again.

Now we'll talk about what your pots are made of. Plain terracotta can be a real problem over time, because some of the water and nutrients which should go to cactus roots instead get drawn away to the porous clay through evaporation. People who rely on terracotta to dry out the mix are using the wrong mix, and even in the right mix, the rooting behavior of their cacti won't respond as well compared to growing in nonporous pots. While plastic and glazed ceramic pots are best, waterproofing terracotta comes in at a close 2nd. I've been getting good results with this. However, I haven't been able to find any sources for terracotta pots that are already waterproofed, so you'd have to do it yourself. Or ditch the terracotta entirely and go with plastic/glazed ceramic pots. Unfortunately you found out for yourself that the garden centers at big-box stores don't offer a good selection of pots that are suitable for small cacti. The "mom and pop" nurseries we used to rely on years ago have been largely pushed out by places like Home Depot and Walmart. But they do still exist. Find out if you have any stand-alone nurseries that are in driving distance for you, and you may be able to find a better selection of the pots you need. If you find them, but it'll have to be terracotta -- at least you can waterproof the pots before you transplant your cacti. What about the proper pot sizes? We'll go there next...

The rule of thumb I go by is to size pots so we have a margin of about 1/2"-3/4" around the root ball. Easy to say, but sometimes not so easy to do. Once again, we don't have to be all that precise, and cacti don't mind if their roots get a bit crowded when they go in the pot. Based on what you've said concerning the fact that the roots of yours are smaller than they should be, their root systems will need to grow in more before crowding the pot becomes an issue. Although it's hard for me to tell for sure from your photos, the only cacti I would call over-potted would be your Cereus peruvianus monstrose, Stetsonia coryne, #7 (yes, I believe it's a Saguaro seedling -- Carnegiea gigantea), and your Oreocereus. You'll just need to use some judgment, so the only basic guiding principle I can offer on this subject is "better under than over". This applies to pot sizes as it does to watering and fertilizing, which brings us to...

How and when to water -- for the growing season only! There are 2 definitions for what we'll call "careful" watering. The first describes what I think you've been doing -- water just enough to get moisture into the mix without letting more than a few drops drip out of the bottom of the pot. Sorry, but -- wrong. Drench the pots like water is coming out of their drain holes like a faucet. When pure pumice is watered from the top that way, it drains quickly and the pumice wets evenly through and through. Soils in a cactus mix may not wet as evenly, in which case you made a good intuitive call when you gave your Ferocactus a bottom-up watering. Some growers claim that bottom-up watering is always the best way to do it, although this is a matter of individual preference, and personally I haven't seen the need for it. The point is to get even saturation and let the mix dry out before watering again. Something else I've noticed in your photos is that you're keeping your cacti on a solid patio tabletop. The problem we'll have there is that while the upper part of the pot dries out, the bottom of the mix stays wet too long as the roots tend toward rotting. To keep that problem from happening, the bottom of the pot needs some air flow. I'll offer a good solution in the form of plastic drain covers, which we can get at Amazon:

http://www.amazon.com/s/ref=nb_sb_noss? ... rain+cover" onclick="window.open(this.href);return false;

You can get these at your local hardware store too, so this just gives you an idea of what to look for. With some decent air flow under the bottom of your pots, your mix should dry out properly from top to bottom. But what about when to water?

The only definition of "careful" watering that's useful as far as I'm concerned is how often we should water our cacti. A common mistake beginners make is to over-water their cacti. You've gone to the opposite extreme, and watering once a month in the growing season is really what doesn't do any favors to yours since they don't have a chance to grow robust, healthy roots. If you resolve your issues with the mix, get your cacti into the proper types and sizes of pots they'll need, and give those pots some air flow so the plants aren't sitting in wet feet all the time, you won't have any reason to be afraid of watering them. Every 2 weeks in spring should be fine, and perhaps summer as well, although you may be able to up the watering frequency to once per week at least for some of your cacti when it's nice and hot. For the species I have that are native to the southwest US and/or Mexico, I've been watering them once a week since June, and they're just loving it. The only cacti I have to be careful about are my Turbinicarpus, since they're prone to splitting if they get overly plump.

There are 2 more things I'll briefly discuss. The first is your growing season, or more to the point how long it lasts. In my coastal L.A. microclimate, the season usually starts in early March and can go well into the end of October. I don't know your climate at all, but I have a feeling that your growing season will be shorter. You may have just enough time to make the adjustments you'll need as your cacti start to reset their roots before they go dormant. If you can pull it off, I think the initial results should be promising enough to take some of the worry out. Otherwise, all you can do is get your cacti through the fall and winter, then see what comes out the other side in spring. And the second is all about winter -- desert cacti shouldn't get watered at all during their winter dormancy. Another beginner mistake, and simply put, the reason you lost cacti over the winter is because their roots weren't healthy enough to take up all the water and nutrients these plants should've been getting in the growing season. After what I just said, I should mention that I can make only a broad generalization about winter care, and aside from the Mamm spinossissima, I don't know the species you're growing well enough to state categorically that you shouldn't water them at all during their dormancy. Hopefully some other members will chime in for any corrections that could help you get your plants through the winter.

[greenknight]

All good advice. I agree that most of those plants don't look over-potted. I would add that, if you must put one in a pot that's too large, putting in some rocks to take up the extra space can work - if you use large rocks. A later of gravel in the bottom is bad, it impedes drainage. You want the potting mix to work down in between the rocks, forming drainage channels all the way to the bottom of the pot.

[Maxy24]

Thank you for all of this information! It makes me feel a lot more confident. So you suggest I go ahead and repot this stuff with the proper substrate and pot ASAP, instead of keeping things as is until next summer?

I'll start keeping them up on a cooling rack or something to help with air flow underneath. The soil used in that photo for my most recent repots is black gold cactus mix which might not have peat, I don't know, most of them are in coast of maine potting soil which I'm sure has lots of peat.

Thank you for all the help!

[Steve Johnson]

So you suggest I go ahead and repot this stuff with the proper substrate and pot ASAP, instead of keeping things as is until next summer?

Personally, I'd go for it -- at least it'll give your cacti a good start on getting their roots established before the growing season ends. To review -- let them settle in for about 2 weeks, then deep watering (and fertilizing!) every 2 weeks until the weather starts cooling off. All I can do is guess here, although I believe you'll have enough time for 3 watering sessions. Could be more, though. This really depends on your climate. Another broad generalization, but when the daytime highs are above 70 and the overnight lows are above 50, the roots should still be active. When those temps start heading south, your cacti will be getting ready for their winter dormancy. Because they still need to get healthy, I'm inclined to deviate a little bit from the "no winter watering" rule. Since you live in MA, bringing your cacti inside for the winter is an excellent idea. The only problem with indoor warmth is that deep watering could encourage growth at a time when they'll etoliate in the absence of sufficient natural light. (Some people use grow lights indoors, but way beyond anything I have experience with. Unless you really know what you're doing, I wouldn't waste the time it'd take to research the matter.) Such being the case, I'll modify my earlier statement about the 2 definitions of "careful" watering. The only use for reason #1 is winter, when the roots could use a little hydration so they're not totally dry all the time. Once a month, and only light watering. I use a spray bottle with the nozzle on the stream setting (mist spraying is a pain in the backside). Moisten the mix all the way around the plant, but don't go overboard and accidentally drench it. My saying here is "sip, don't soak". And water only, we'll save the fertilizing for when your cacti are ready for action in the growing season. While we're on subject...

I mentioned my Dyna Gro All-Pro 7-7-7 earlier, but we can only get it by the gallon. Since you have a really small collection, IMO it's kinda hard to justify the expense. Dyna Gro makes a 7-9-5 liquid fert in smaller quantities, and the nutrient profile is about as good because it includes the minor nutrients and micronutrients we'll get with th 7-7-7. You can find the 7-9-5 through eBay:

http://www.ebay.com/sch/i.html?_trksid= ... &_from=R40" onclick="window.open(this.href);return false;

Dilute 1/2 tsp. per gallon of water. A low but steady level of NPK is excellent for strong, healthy growth in cacti -- that's what we're doing here. If you're growing them in pure pumice, fertilizing every time you water is a requirement. If you're using a pumice/soil mix, you can skip the fert from time to time. With that said, don't start skipping until after your plants are clearly healthy and growing. You're a long way from that point yet. And if you're watering your cacti with hard water, I cannot emphasize enough how important it is to acidify the water. If the idea seems a little scary and you're not able to store rainwater, here's an alternative -- water your cacti with the distilled water you can get at the grocery store. Easy as pie, and the only thing you'll need to remember is adding in the fert.

The soil used in that photo for my most recent repots is black gold cactus mix which might not have peat, I don't know, most of them are in coast of maine potting soil which I'm sure has lots of peat.

Might be fine for leafy houseplants, but commercial potting soil manufacturers don't have a clue about what desert cacti really need. Anything called "Black Gold" makes me nervous. I've been investigating eBay more and more these days, so the following might have some promise:

http://www.ebay.com/itm/PS-NATURES-POTT ... 58b219951f" onclick="window.open(this.href);return false;

Could PS Nature actually have it right? You'll have to find that out for yourself. As soon as you have an eBay account, you can email the seller through eBay. Don't have the need to spend a lot of time there, but the sellers I've dealt with have been quite responsive. If you want to pursue this, I'd highly recommend contacting PS Nature immediately and ask them about the specific ingredients in their potting soil. If they respond quickly and are forthcoming about everything that's in the soil, you may have a winner. That is, if it doesn't have any peat! Some cactus growers have no problem with peat, but it sends up nothing but red flags for a lot of others. Me included, so I really hope for your sake that the seller is giving you a peat-free product. The other thing you'll need to ask is if their amendments include some built-in fertilizer. Not necessarily a deal-breaker for you, although I freely admit that I'm a control freak, so I want any and all ferting to come from me, not someone else.

I just love getting into all the details that go into successful cactus cultivation. And it certainly is a lot of fun to pass along what I've learned for the benefit of those fellow hobbyists out there who've been struggling with their plants. Your window of opportunity will be drawing to a close soon, and I really hope you'll be able to put everything together for your project in the next week or so. I'd be interested to follow your progress -- by all means, please keep us posted!

All the best, and happy growing!

[DaveW]

How do you know when they want watering? Experience. and you will still get it wrong at times and loose plants. Anybody who has not lost plants in their collection over time is only just starting or has not grown many.

Many commercial nurseries use pre mixed potting soils Steve, or at least as one ingredient in their mix so they don't always know what all the ingredients are. In the UK in the past John Innes composts used to be the starting point for many of our cactus mixes, but at least their formula's were published, many proprietary ones are not.

The problem also is proprietary mixes often change their ingredients according to what is available and best current price, say substituting composted materials for peat if the price of peat rises, and the same applies for any other ingredient. I think James raised the point that a different batch of pumice from the same commercial source was not the same as they had supplied in the past so had different characteristics. Therefore even if you mix your own soils using commercially supplied materials you cannot always be sure the ingredients will be consistent over the years, or even still available if a firm closes.

There are probably as many potting mixes as there are collectors, and many will only be appropriate for those growing plants in similar conditions and climates. We all experiment with our potting soils until we find what suits our conditions. However whatever you use it needs to drain quickly and not retain moisture for too long, though you can get away with mixtures that hold water longer in hot countries where drying is quicker than in cold ones. Though with our plants, unlike conventional house plants, you will loose few from keeping them in the dry side until you gain experience rather than over watering.

The Northern Europeans seem to write more books on cactus culture than the Americans (John Pilbeam's books = UK, was mentioned elsewhere, as was the Austrian Franz Buxbaum), so you cannot just take recommendations for European cactus culture and simply transpose it even to the hotter parts of Europe, let alone the America's. You need to modify them for your conditions. Perhaps somebody should now be writing "Cactus Culture for California" or "Succulent Soils for Spain"? There are a few relevant links on the web though if you search:-

http://hort.ifas.ufl.edu/floriculture/p ... 04-006.pdf" onclick="window.open(this.href);return false;

http://toptropicals.com/html/toptropica ... acti_e.htm" onclick="window.open(this.href);return false;

Also in some less favourable climates they often treat Succulents like bedding plants, putting them out in the growing season and bringing them in for winter:-

http://www.gardeninggonewild.com/?p=3666" onclick="window.open(this.href);return false;

Even some of the big European cactus nurseries who have to grow under glass remake their centre beds each year, either covering plants grown in pots with gravel to make them look bedded in, or even replanting every plant to maintain spacing just as one would re-pot if in pots. See De Herdt's Cactus Nursery centre bed in this link which has to regularly be remade and re-spaced when the closely packed plants quickly grow together:-

http://northants.bcss.org.uk/nl201/tour.htm" onclick="window.open(this.href);return false;

[greenknight]

One thing I found helpful was to put some fair-sized rocks on the surface of the pots, where there's room. Clear away any other top dressing, and press them right down into firm contact with the potting medium. To check the moisture level in the pot, pick up a rock - if the surface under the rock is damp, you know it's nowhere close to needing water. If it's dry under the rocks, it will be needing water before long - maybe not quite yet, but it's getting close.

[DaveW]

A similar effect to the above. If you top dress your plant pots, often if you look at them early in the morning before the day warms up the top dressing grit will look damp if they don't need watering, but it dries quickly as the day warms up.