With respect to cacti, I believe cooler temperatures and lack of watering sends them into dormancy.

Planto

There are several clues to follow.
First of all, I don't know of any plant that follows a hemisphere after it is re-located in a different one. do you have examples?
Secondly, in my experience, as many plants go dormant when high temps come, that is, they are dormant in summer during the hottest part of the year. Some go dormant when cool temps arrive, the trick is to determine which side of the fence it is on before you kill it. My compost pile is full of wrong guesses.

Plants that sleep during the summer often awaken in the fall. clues are a change in the color of the spines (some South American models), flowering if the plant is old enough, or a noticeable loss of turgidity (the plant/leaves go limp). This limpness indicates the plant is using more water, so that something as simple as a Jade that has maintained hard leaves with little water suddenly has soft leaves with the same amount of water.

Some plants growing new spines have the last ones turn color at the base. I'll see if I can dig up a photo of that. Spines that had been grey for months had the base of them turn color when new spines started to grow.

Maybe somebody can elaborate on why this is so, the reason is beyond my knowledge, but I'd like to know.

It is my understanding too that a plant has it's own clock and will follow a pattern from it's native land no matter where it is. So I would love to hear more on this.

I raise parakeets, and in Dec. they breed like crazy! They are from Austrailia (sp?) and in their native land, Dec. is spring, and although they have been in the US for years and years, they still follow the native schedule. So I could see how a plant would too.

The best thing to do as far as knowing when a plant is dormant, is to research each plant.

Dzitmoidonc, shared some good tale tale signs too.

The majority of what I have kind of have 2 seasons. Active in spring, rest in the heat of summer, and active again in fall, rest in winter.

JoJo

As I understand some grow in the winter, some are dormant in the summer, some are confused and follow the seasons from the hemisphere they are from

It is a basic understanding you already have and also something that would need perhaps one or two knowledgeable speakers to explain in more clear to understand detail.

For what it's worth
True the plant doesn't know where it is... As plant growers we try to make it feel at home, although our home isn't always a plants home. I dont think the plant gets confused it is the one who grows that plant that's confused.

Nothing personal toward you some of us have have made the plant feel at our home not it's home.

Suggestion for you is to break your succulent plants down into two more groupings... Group one: old world separated from new world. Group two winter growing from summer growing.
Develop a better understanding that in the old world group the same family of plants growing VS. dormant times sometimes changes with in a few miles of the areas they grow naturally. At the same time in new world group most succulents are resting or growing regardless of whats going on in the old world.

Mostly North and south hemisphere is the plant dormant/ rest time factor but it's also in the flow of air pulling or pushing the colder /warmer ocean currents,and elevations. Not easily explained with out use of maps and diagrams.
Best thing is to listen to a speaker for about an hour or two there are some people in all C&S groups who have been to the places you ask about that could explain it better than any ole keyboard.

I keep a colored straw in my plants.
Red(hot) is summer dormant and Blue(cold)winter dormant. It helps me to keep track until I can better learn my plants.

Mrlike2u~ dividing into the groups as you suggest is a great idea. Now that winter is sneaking up.. and I'm a big baby about cold, I will use the time to research and get to know my plants better and work on grouping them. :-)

JoJo

Lots of information to digest. Thank you all for your input.

So reading about each plant that I have, is it generally good to assume that plants that "shouldn't be watered in winter" are winter dormant? I keep a detailed journal of my plants so I know which ones shouldn't be watered in winter. But rarely do I find information that says specifically when they grow and are dormant.

And more confusing and frustrating is that when you read about dormancy and wintering ones plant people are talking about really cold places. Here in Southern California we have 70 degree weather year round almost. It's just that we get more precipitation in winter and cooler nights. So are my plants going to go dormant? Heck I don't know :) This sounds like an smart phone app! Punch in your zip and what plants you have and it will tell you when they are growing or not :)

I tried to grow some baobab trees a couple of years ago, from seed. And reading about their needs I believe I read that they grow when there is summer in Africa regardless of where in the world they are. But that could certainly be misinformation.

robinpla, to confuse matters further, some are opportunistic growers. This means that as long as conditions are right, the plant will grow. For instance, many Mammillarias will grow most of the year for me. Only long dry hot periods (weeks of what we call drought here) causes them to shut down. If the rains return in September after a dry July and August, you learn pretty quick what plants were sleeping.

Some African Euphorbias will surely rot if they are watered in late summer, but bloom and grow when nights get down below 50F and they have wet feet for days in December and January. Enopla, anoplia, suzannae, zanzibirica come to mind.

The heat here in Pennsylvania is nowhere near what one gets in Tucson, for instance. So the same plant that goes dormant for them might continue growing me even in July. Rule of thumb: bloom, leaves, change in color means growth.

Stapelias rest in the winter. The nicest (an opinion) Pelargoniums are summer dormant, wish I had know that before I grew several from seed. They did well year-round until they started blooming. Then they did the summer dormant thing. I insisted they continue growing like the year before. They had the last word when the roots rotted and the plant died. Acquired wisdom can be cruel and humbling.

The link contains a winter/ summer rain map of the more complex country of S. Africa to help assist in winter summer growing succulent plants and S African bulbs sorting.

As reminder rain means plants have an opportunity to start new growth.

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Plants have a lot of mechanisms for determining if they should grow (actually it's the factor that restricts growth that relaxes at these times, but that's not a useful distinction for growers, generally).

I think the big three factors are, in no particular order:
1) Light levels (including length of day--they can sort of 'know' in this way which hemisphere they're in, among other things)
2) Temperature (in fact, many plants have a sort of chemical clock and 'know' how long it's been since it was a certain temperature--useful for coming out of winter dormancy at a safe time)
3) Moisture levels (this is an obvious one and the one we can most readily control as growers)

The specific climate, via some combination of the above, generally determines which conditions and timings are favorable to growth. Usually it's the rainy season, unless the rainy season is close to winter in a temperate area or the like (in Seattle the summers do get fairly dry in Jul-Aug, so I think most growth happens in spring, then again in fall, except for deciduous trees and the like, which are busy readying for winter). There are almost certainly exceptions to this, though.

Based on some quick searching, BTW, it looks like the Baobab is no exception--it'll grow when it's warm (as it grows during warm, wet seasons in its native areas, at least A. digitata in Africa and Arabia). With water provided by the grower though, it'd probably come out of dormancy in spring/summer in temperate zones. Maybe that's where that idea came from.

I don't know if any plants do have a memory of their native seasons, but it strikes me as possible, if a bit unlikely (seems like pointless information, but maybe there's some case where it'd be useful).

Even seedlings can do some pretty complex timing operations--for germination it's probably the most critical that they get things right--but this mostly does hinge on ambient conditions, in all of the cases I'm familiar with. The mechanisms for this are basically all about chemical levels and genes being activated or inactivated by environmental conditions or other genetic processes--specifics are only fairly recently forthcoming, but anyone who's done cold stratification or something similar is accounting for these processes.

Not sure I can offer advice, other than what's been stated. Softening succulents are either rotting or in need of water--usually it's trivial to tell the difference. Attempted growth is my usual measure, except that I have plants that are either predictable or opportunistic. I lay off the water unless I think I can convince the plant it's the growing season by watering--which of course depends on the proclivity for cool or warm season growth.

Awesome Hexalm. Thank you for your help. The more I read about this the more I realize you have to really know your plants, get to know them personally, and watch them throughout the seasons.

I have had this website bookmarked for a while. Never really used it, but though it could come to use some day. Do you think this watering recommendation from Germany applies to my plants in Southern California? At least it indicates when they are dormant and if they want complete dry dormancy or some water. What do you think about this:

http://www.specks-exotica.de/en/cultivation_data.html

Hmm, interesting page. I think it's probably applicable, for the most part. I didn't examine any of the specific suggestions, though.

It looks like they're just tracking growth season, probably based on temperature--if that's the case, you're in the right hemisphere, at least.