I know this is a weird question but bear with me.
I really like the stressed and very spiny look on my plants and that's why i grow them in full unblocked sun from sunrise to sunset. However, i don't like this look on 1% of these plants like echinopsis sundenudata, cereus, aloes, haworthias...and i would like them to look plumper and with fuller leaves. I have a big subdenudata that has been growing happily for 2 years and is actually still smaller (in volume) from when i bought it. You know how these come so plump from the nursery that they are about to burst.
So anyway, this is what i'm thinking of:
1. No full sun from sunrise to sunset, maybe only for a couple of hours and under 30% shade. Anyone knows how many lux commercial growers keep in their nurseries?
2. Since my universal mix is 2 parts grit and 1 part compost i'm not sure what to do here: water more often or use a more water retentive mix?
3. Fungicide or not? I occasionally use povidone-iodine in water or on scars but i'm not sure how that will fare in the long run.
That's what i got so far and any tips are welcome. If they do it on such a widescale in wholesale nurseries then it must be something easy i guess. I know they use cappillary mats but i don't think that will do well with a gritty mix

There is only 1 full proof way of watering plants safely, with a syringe. As funny as it sounds, its the only one without splashing and with regulated flow control.
Thing is , you need to be exact with the dosages, and the timegap of the waterings.
EG, been told plants like melocactus, parodia and echinopsis like water in winter, but astrophytum, eriosyce, gymnocalycium, rebutia should be waited until new growth emerges...
Now of course, how much should you really give them also matters....

CCG, I forget if you told us where you are, it sounds like it is a mostly frost free area, but what are your day time highs throughout the year.

Here where I am in the Phoenix AZ area most Echinopsis plants tend to not take the full summer sun, so I grow the many that I have in partial shade, however any Trichocereus types can be adjusted to full sun. My sense is, if your plant is used to full sun, why not leave it in the sun, but change your watering scheme.
Most Echinopsis plants develop large root systems so contrary to many other cacti, they do enjoy being a little bit over potted (still better not to go too crazy, but give them plenty of space). In my experience these can take more water than most cacti even when it is not super hot, but again they do not like to be too cold and wet for too long and they are still cacti so you do not want to go too crazy with the water. It sounds like your mix is fast draining which is going to help with that.

I would see if increasing your watering frequency helps, if that by itself does not get you the desired results you could play with sun exposure, but I would certainly not move this plant from the full sun to something that sounds like it would be almost full shade, your plant would probably go all etiolated pretty quickly. While moving a plant to more shade does not need to be done with as much care as moving a plant from shade to full sun, drastic exposure changes each way will still affect the plant. You could also add some fertilizer your mix, is on the lean side when it comes to nutrients from the sound of it, adding some half strength fertilizer to your water say every other watering might also give the plant a boost.

I grow most of my Echinopsis plants in about 1:1 pumice - cactus soil, in my experience I need to repot those about every 3-4 year because by then there is nothing but pumice left in the pot and while pumice is great for the roots in terms of aeration and how it retains some but not a crazy amount of water, it is a poor source of nutrients.

Interesting what you say about not reducing sun exposure. I forgot to mention that my subdenudatas (like 7-8 of them) are in part sun in summer and full sun in spring. If i leave them in full sun in summer, their growth will be stunted. Ehchinopsis oxygona does extremely well in full sun all season long. I have a very big one in a deep 10 inch pot that's living in pure sandy soil and it's doing so well. I'm too lazy to repot it. These aren't very finnicky.
Yes i do live in a frost free area (zone 11a) but we do get a random frost every couple of years years (maybe 2 years maybe 5). A few years back my poinsettia tree turned to gello overnight and i had to cut it back to the main trunk. It came back nicely in spring.
Anyway back to overwatering...i remembered when i applied systemic last year. I soaked the pots in the solution for like 20 minutes and a couple of days later the plants looked plumper than usual ( but to be accurate im not sure if it's because the root mealies died or because of the soak). However, i have some pots that sit in tiny puddles of water since the benches are not completely even and flush and these looked plumper than the others. So my new idea is to either soak the plants for 30-60minutes when i water or put them in a saucer. If i water in the evening, the collected water in the saucer will be evaporated by noon the second day in full sun. Maybe i'll try both come spring.

I water in more than one pass. Dry soil resists absorbing water anywhere near saturation until it has become moist. Try watering, then returning in 10-15 minutes to water again. You might want to do another couple passes if the pots are unusually big, because it takes time for water to penetrate the center of a big volume of soil. More on the subject here.

The thread "Sunday afternoon experiment: watering in multiple passes" in Gardening Ideas forum

I have a couple problems with this whole conversation:

1. You want advice on plants you keep outdoors but are not willing to share your location.

2. What is the problem with just watering a little more often?

I'm going to guess Canary Islands based on: northern hemisphere, metric units, Mediterranean climate, zone 11a. Am I close? You don't have to answer, of course.

Back to the original question, some more feedback from my experience.

1. (filtered light) I have tried different degrees of sun protection from 20% to 50% to 70% and currently have the latter two in operation, plus direct sun up to all day long. My advice is based on a very mild climate (no heat here) so your mileage (kilometrage?) will probably vary. Consider this a look at the effects of light more than heat. We are subtropical. I use and recommend a light meter.

Also bear in mind that walls and structures (and shade cloth areas) create shade in a variable way through the course of the seasons. Overhangs can serve a valuable role in late spring and summer, especially for very young seedlings. A southerly exposure is good in winter; an east or westerly exposure is best in summer. A northerly exposure is to be avoided at any time of year unless it's a rootless cutting which is not likely to root any time soon.

Most of the succulents I grow under 70% shade get the lid lifted on a semi-regular basis (it's up and away right now on a cloudy day). I wouldn't really go 70% shade all the time except maybe for variegated plants. Otherwise they look a little wrong to me growing in that little light. I'm not into perfect plants, but soft is not my style.

50% shade is a good working strength for young seedlings, cuttings, sensitive Aeoniums in summer, crests and oddities. Nobody stretches and those plants grow more than they would compared to a control in half-day sun. As soon as they're going strong (usually graduating from a 15cm pot) they can go into 20% shade, up until 25cm size or indefinitely, and that small amount will give better results than half a day of direct sun. Some plants are ready for full sun really early (at the 20cm size) and those would include barrel cacti, agaves, most aloes. I hustle everybody out into the sun as fast as they can go. Not a lot of real estate under shade cloth.

This time of year full sun is nowhere near its late spring potency. There is more shade and more of a southerly aspect to the light. Northerly sides of walls or structures are in full shadow. It's increasingly harder to sunburn or sunstress the plants that I grow this time of year, even in maximum full-day sun. Everybody looks pretty good no matter what after it rains in the winter, but maybe that has less to do with the lower light and more to do with their relative filth.

2. (soil) I am a big fan of coir (coco fiber) which is fabulously moisture absorbent and long lasting. My recipe these days is 50% pumice, 25% potting soil (locally made, mostly compost), and 25% cocofiber. After that compost breaks down and turns to dust years later, it's 2/3 pumice and 1/3 cocofiber. I have seen plants in Southern California that were grown in 50/50 cocofiber and pumice, and they were pretty sweet indeed. Obviously that would be a hydroponic situation. In our dry climate the cocofiber is really helpful, especially if you're lazy like me and don't like to repot more than necessary. You don't want to overdo it, and you might need to adjust your watering regimen after including it, but I like the longevity and the water absorption.

I still would recommend watering in more than one pass as a relatively easy first step.

Crazycactiguy said:Interesting what you say about not reducing sun exposure. I forgot to mention that my subdenudatas (like 7-8 of them) are in part sun in summer and full sun in spring. If i leave them in full sun in summer, their growth will be stunted. Ehchinopsis oxygona does extremely well in full sun all season long. I have a very big one in a deep 10 inch pot that's living in pure sandy soil and it's doing so well. I'm too lazy to repot it. These aren't very finnicky.
Yes i do live in a frost free area (zone 11a) but we do get a random frost every couple of years years (maybe 2 years maybe 5). A few years back my poinsettia tree turned to gello overnight and i had to cut it back to the main trunk. It came back nicely in spring.
Anyway back to overwatering...i remembered when i applied systemic last year. I soaked the pots in the solution for like 20 minutes and a couple of days later the plants looked plumper than usual ( but to be accurate im not sure if it's because the root mealies died or because of the soak). However, i have some pots that sit in tiny puddles of water since the benches are not completely even and flush and these looked plumper than the others. So my new idea is to either soak the plants for 30-60minutes when i water or put them in a saucer. If i water in the evening, the collected water in the saucer will be evaporated by noon the second day in full sun. Maybe i'll try both come spring.

Are they stunted or sunburnt? If they are sunburnt they cannot take your summer full sun, if they are stunted they are probably just not getting enough water. As said when it is hot these guys do not mind getting a good amount of water.

Soaking pots in a basin for 30-60 minutes or watering in multiple phases like Baja does are definitely very helpful to get plants hydrated, plump and growing. However I probably have over 150, possibly 200 potted plants (I have never counted them so it could be more as I have about 80 Echinopsis cultivars alone, not all different, but plenty are)... am combining this 'hobby' with a full time job in academia so watering has to be a one size fits all kind of exercise. In the summer, if I can I water my plants once a week with a hose. All the potted plants get watered till the water runs through the pot.
Only plants I water more are any seedlings and my Adeniums and maybe a few other plants that are all located together near the seedlings. Is the only way for me to manage watering everything (given that I have a lot of plants in the ground as well). What really helped my plants in the summer is something I noticed after we got some really uncharacteristic late spring rains: if I water them more frequently and generously in the spring (ie. go to my summer water regime in April iso June) they get through the summer better.

I'm gonna try to answer everyone in one reply.
Baja_costero: yes i always try to water in 2 passes when i have the time. It helps a lot with getting the soil saturated but most importantly reduces salt deposits which are a real problem for me worh out very hard tap water. Acidifying helps but flushing a second time is key.

Daisyl: now i respectfully have a couple of prroblems with your reply
1. I'm not asking how to care for my outdoor plants. I have several 100s living happily. I'm asking for 1% of them how to simulate nursery condition to get them to look plump and full like when you buy them and before subjecting them to more extreme cinditions.
2. Not sure how my locaction is relevant. Since the start, it's written in my signature (?) that i'm in zone 11a and have lots of winter rain which is more than enough i believe.
3. Why not water more often? I try to water as soon as my plants dry out so i can't water more than that. What i'm asking is how to get the plants to absorb more water/lose less from conditions

Baja_costero: not thr canary island but quite close relatively
Consider the effect of heat more than light: but they are mutually exclusive. The more sun a plant receives, the more hot it gets and the more water it loses (mostly from its soil). This is thr first time i've heard about such mild weather i your area. I thought for sure you hit 90s and 100s in sunmer.
I have lightmeter in my smartphone (it's free from the app store) but i'm struggling in finding the necessary level. All i find online is cannabis related.
I found it usually that the sun is strongest to the east which is rather weird. This has caused my columnars to have a very annoying tilt to the east.
I think i'm gonna take you up on a 50% shsde cloth with all day sun rather than part sun. Yes i'm not a fan of soft plants but i would prefer that over succulents with literally paper thin leaves. I've never really used a shade cloth and all my cacti go immediately into full sun (after a couple of weeks part sun to acclimate). I really like aggressive looking spines and i'll take that any day over fast growing plants. My pride was an eriosyce bulbocalyx thst i grew from seed and it took 7 years to get to a 4 inch pot. But man it has some crazy spines. You could not see the body unless it was well watered. Unfortunately it's dead now. I attached a photo of a bunch of cardons i grew from seed. They have crazy long and thick spines and are starting to look bluer thsn my pilosocerei. A buddy of mine grew his at the same time and they are substantially bigger than mine but have weak thin spines and look very green with not a hint of blue.
Back to replying, truth be told, i'm not even half as brave as you to leave my plants out in winter though they would probably take it. They could use a wash and some acidic rain to remove carbonates but they'll have to wait for spring rains. Boy do they look amazing after some rain, especially the barrels.
Now for soil, i would love to use coco fiber since i've only heard good things. The thing is i've been using the same mix for years and often pot plants up rather rhsn repoting everytime. Using coco fiber would mean i have to repot every single plant or else there would be a difference in drainage.
Anyway thanks for all this great advice!

Mcvansoest: no just stunted though thry get plenty of water. As soon as i move them to part sun they hit the kickdown switch. Though i water in 2 passes at night to give them time till morning to drink well, i'm starting to think some plants are not well hydrated.
As you say, watering almost becomes a full time job so i'm only gonna soak the succulents and the subdenudatas. As for adeniums, for me they live with the mature cacti. They take full sun easily which makes them flower profusely and get the same water but so much more fertilizer. I bring my plants out in very late winter to early spring and i don't water much in this period since it rains very conveniently once a week i have to say that they look much better in spring and they only have a bunch of roots coming out of drainage holes in spring rains (never in summer). Come to think of it though, last year they were in rain for 7-10 days straight and not a single plant burst from too much water. So maybe my soil is not that water retentive but i guess it's good safety measure.
Oh and btw, i often don't water in midsummer since i'm mostly away but a big number of plants are dormant. This way i don't have to look for who needs water and who doesn't. Better safe than sorry
I blabbed too much. Thanks everyone!

You are probably in the azores or maderia then.. ....

Crazycactiguy said:Consider the effect of heat more than light: but they are mutually exclusive. The more sun a plant receives, the more hot it gets and the more water it loses (mostly from its soil). This is thr first time i've heard about such mild weather i your area. I thought for sure you hit 90s and 100s in sunmer.

Light and heat can be separate effects of sunlight and they are here. Light will drive evaporation but it will not heat up plants if the baseline temperature is mild (our daytime highs are generally 15-20°C) and there is good air flow (like our ocean breeze which is a steady daily thing). My plants do not generally heat up in the sun. What may heat up, depending on the setup, is the pot, which will tend to cook the roots on one side if it is exposed. For that reason I try to group my plants so that all of the ones past the front row have the sides of their pots blocked, and I use shelves placed at a level such that the walls of the patio block the sides of the container but not the top. The deleterious effects of heat mostly have to do with the roots in my experience, and there is no faster way to cook them to death than to leave them in a dark ceramic pot with its sides exposed to the sun.

Most of Baja California is hot and dry but there is a sliver on the NW corner near the Pacific Ocean with a climate very similar to coastal Southern California. The prevailing winds in this area are onshore and the ocean temperatures are much colder than average for this latitude because of the coastal upwelling. We get to just above 90°F for our annual high.

Crazycactiguy said:I have lightmeter in my smartphone (it's free from the app store) but i'm struggling in finding the necessary level.

I don't think there is a necessary level. I would go by a relative fraction of full strength late spring sun. Our total solar energy at midday (measured in J/m2) varies about 2 fold over the course of the year. We are at 32° north latitude. Thus direct sun at midday around the end of the year is equivalent to 50% shade at midday in early summer. My dedicated light meter was really cheap (like $10 or $15) and its performance is reliable. You can get a very good sense of the relative strength of the sun by looking at its angle in the sky, to which it is quantitatively related. At the summer solstice the sun reaches over 80° from horizontal (which is nearly vertical) and at the winter solstice it reaches just over 30° from horizontal (which is 1/3 of the way to vertical). I use a local weather station which reports the solar energy (J/m2) and the UV index which are both good estimates of maximum sun on any given day.

Illustrations here to show how I avoid cooking the sides of the pots of my succulents.... photos taken in morning sun.

This low wall faces SW and blocks the sides of the pots (only) from sunlight after late morning. This is a rooftop patio so there is no shade otherwise, except for what the plant on the wall might generate.



Small pots have their sides mostly blocked by other small pots and a plastic tray.



This shot taken from the angle of the afternoon sun, to show how these pots are aligned to expose the tops and shield the sides, beyond the front row.

Yes cooked roots are the reason i stay away from black pots. I like to group pots together or cover their side. This will also increase thr longevity of the pot.
So straying off from topic but what you showed reminded me of a couple of questions i had...
1. Where do you guys stand on top dressing? I like the safety that comes from the rapid surface evaporation but besides aesthetics, i guess a little more water retention will result i healthier (uncooked) roots and plants. I anchored some tall plants after repotting with some stones and found out that after a while roots had come up to the very top under the stones. I never have roots in at least the top 2cm of the soil on my pots with no top dressing. I think of it as keeping excessive moisture away from the crown of the roots.
2. 5.5cm/2.2" pots: these dry out too fast and i can't imagine 66% grit of such a tiny volume is very nutritive. So i was thinking of ditching my standard mix for 5.5cm pots only and going maybe 90% organic. This way the soil will not dry too fast before the plants drink. And since 5.5cm will be holding very small fragile plants, i guess the increased water rentention and nutrient availibilty will give the weak plants a stronger start. How do you guys manage your 5.5cm pots (besides daily watering)?

I don't use pots smaller than 10cm. Too much watering required. I refuse.

I like to use chunky pumice (basically a monolayer) as top dressing. Sometimes I use red lava rock. The advantages: uncooked roots, some aid with water retention in the upper layers (but not a huge difference overall as water passes freely through pumice), UV protection for the soil, more volume available to the roots.

Here is how I currently grow my cacti at my home including the soil mix I use, my watering & fertilizing regimen, containers, staging, etc. …………..

http://jp29.org/brcult.htm

…………… as you can see I mostly cultivate terrestrial Brazilian cacti, specializing in Micranthocereus, Arrojadoa, Coleocephalocereus, Uebelmannia, Discocactus & Melocactus. I also do house most of my mature and specimen Brazilian cacti in a commercial green house at Dan Bach's Cactus Nursery here in Tucson. Dan is an old and dear friend - our friendship spans forty-five years - and he very kindly provides me greenhouse space for free - he is a great friend indeed. Most of the cacti that I house there are in large pots on benches - others that are very large are on the ground. They are now mostly maintained by Dan's work staff because It is very hard for me to journey to the Nursery (about five miles distance) these days due to my disabilities. I only go there about once per week now. As a point of interest, about half of my plants there are growing in an organic based soil mix and the other half in a mineral based soil mix.

As you will see from my web page, I am mostly a windowsill/plant box grower here at my home now - I (hopefully) explain and discuss my cultivational techniques - soil mix, containers, watering, fertilizing, sun exposure ……… and so on, there.

I am not saying that my techniques and methodologies are better than any other enthusiast here — or even as good as some —I just want to participate in this very interesting interchange of information and ideas.