(Editor's Note: This article was originally published on November 15, 2010. Your comments are welcome, but please be aware that authors of previously published articles may not be able to respond to your questions.)
Though I still always fall for it, whenever I see a remarkably colored aloe, agave or even cactus for sale, I am tempted to get it, even though I know that its color is probably a sign of stress. Though this "stress" coloration is often a normal condition of the plant in response to environmental extremes, it is often a temporary condition that will likely disappear if I take good care of the plant. And though occasionally these stress changes may be signs of unhealthful conditions, more often than not they are ones that these plants have adapted to, for whatever reason, and are still well within the normal range for continuing life. Not all stresses are normal and knowing what is normal versus what is not can sometimes help one act before it's too late. The following discussion of stress signs and changes in succulents are limited to macrobiotic changes. There is probably a long list of complex, microbiologic and chemical changes that are probably very interesting and amazing, but those are well beyond the scope this article, and this author as well.
Got this cool looking Aloe suarzensis, because of the colors
But then I planted it, and in just a week it was greening up (left) and now, a month later, it's no longer so cool looking (right)
Color change. Most color changes in succulents are fairly normal and are a response to either excessive cold, heat, sun, nutrient deficiency or drought. Some plants are collected and purposefully stressed just because of the brilliant and ornamental appearances these amazing plants take on under these situations. I collect aloes in particular and some of these are among the most versatile and variable of the succulents in terms of color change. However agaves, cacti and other succulents often change color, too, some with spectacular results.
Both Aloe aculeatas are in full sun, but one is getting plenty of water (left) and one is going through a long drought (right)
Aloe brandraaiensis colony getting rainfall, but showing some leaf-tip necrosis stress (left); this plant on right showing some other stress (heat?) and marked color change (photo Kell)
Aloe classenii (same plant in both photos) in fall (left) and spring (right)
Aloe garipensis in spring (left) and fall (right)
An Aloe ramosissima in hot, dry summer (left) and another one flowering in cool, rainy winter (right)
These Aloe cameroniis are one of the most popular red aloes... but why some are green and some are red is unknown... perhaps there are microstressors affecting one sucker and not the other
Crassulas often have color changes, too, with stress (usually heat as in these shots of Crassula 'Campfire')- left is in winter and right is the heat of summer
And these show similar seasonal stress changes from heat (right) and more 'normal' but less interesting coloration in winter (left)- Crassula platyphylla nudicaulis
Sometimes color changes are not just limited to red or green. These 4 photos of Sedum x rubrotinctum 'Aureum' show a wide variety of color changes as its environmental stresses change throughout the seasons
often just being in a pot is a huge stress on a plant mostly because it is more exposed to temperature changes (the soil temperatures tend to be more stable in the ground than in a pot), and soils in pots tend to dry out much more than soils in gardens. This Echeveria agavoides is showing wonderful stress colors in this show plant (left), but more normal coloration in my garden (right)
Sometimes it's hard to tell stress coloration (left) from a more normal coloration of these hybrid Echeverias (right), though they still are showing stress coloration, just a bit more 'normal' stress coloration
Dudleya caespitosa showing stress coloration, as well as shrinkage (left) in summer, and looking happy and pale blue as ever (right) in winter
Some stress colors are a bit unusual- Sedum nussbaumerianum get nice and orange with the right amount of sun, heat and drought (left)- they are completely green in shade; Aloe petrophyllas get a weird olive-orange in summer heat (green in winter)
Sometimes a colony of plants will only be partially stressed with a few showing color changes from lack of water (usually). Left is a colony of Haworthia coarctatas and right is a clump of Euphorbia submammillaris
Euphorbias also can show amazing stress coloration, as seen on the left of this Euphorbia tirucali, or Sticks of Fire Pencil Cactus... however, these maximally stressed plants in this nursery were purposely stressed to sell, and once planted in a situation where they may not be in as much full sun, or getting more water (like mine on the right), the coloration is less than outstanding.
These four shots above show Euphorbia mammillaris variegated in several different environmental situations- upper left in a greenhouse and well watered; right outdoors but still in shade and less well watered; left lower is a desert-grown plant in full sun and minimal water, and right is a plant that was in too much shade, and now in full sun and absolultely no water (this is known as too much stress).
And asclepids also show normal color changes depending on time of year and heat/sun exposure (Stapelias above in spring (left) and fall (right)
Cactus can show stress color changes, too, though less commonly. The Echinopsis on the left are stressed mostly due to heat and drought, and the Thelocactus rinconensis on the right is a nice reddish color most of the year, but 'greens up' (actually turns a grey-brown) a bit in full shade and plenty of water
Some of the most spectacular stress colors in cacti can be seen in these Opuntia gosselianas, which turn from a beautiful deep turquoise to an even more striking purple-pink when they are severely dehydrated and overheated. This is a normal stress color, but with continued environmental torture, it will not take this cactus much more to go to the next step- necrosis and/or rot.
Though not normal for many cacti, this normally dull grey-green Copiapoa hypogea (as in left photo) can turn a sickly orange-brown (right) from severe dehydration and high heat but still be fairly healthy. One really has to know the limits of their plants or one may end up with either a pile of mush, or may be overwatering a 'normal' color extreme.
Two shots of same garden northern California: left in March and Right in August, showing stress color changes (photos by Kell)
Not all color change is good. Sadly, despite my propensity to take tens of thousands of photos of plants, for some reason I do not tend to take photos of dying plants, even though these images would probably be good teaching tools. I will work on that.
The color of burn- though burning is obviously a bad thing for plant tissue, it is not always a sign of dying of the tissues. Burns usually appear first as a lightening of the normal color of the plant (starts out as a blanching), sometimes eventually turning to the all-too-recognizable color of dead plant tissue (pale brown). Some cactus and agaves have remarkable regenerative powers and can repair burned tissues, replacing them with normal colored tissues. Other burns result in permanent scars. And badly burned plants will sometimes succumb to rot or just outright die.
This Echeveria subrigida is one of my favorites, and it changes color all the time with the seasons. However, this year's heat has been a bit too much for it, and though some color changing in the blanching range is normal for this plant, the color changes on the right are into the abnormal and unhealthful range. Still, it will probably come back...
The Aloe 'Goliath' on the left is blanching a bit, showing abnormal stress changes on its leaves. These changes are relatively permanent. The Echinopsis on the right is showing less permanent blanching
This Aloe melanacantha on left was happily growing in a bit too little sun, but doing OK. I knew it really should be a full sun aloe, so I moved it there. And this color change on the right was noted- the color of frying tissues. Not a good stress coloration, and the plant dies soon after
This Aloe polyphylla began to show these weird color changes during a particularly bad heat wave (over 110F) and though it was NOT in the sun, the heat alone blanched this alpine native plant. It was dead soon after.
I moved this Agave horrida from semi shade to full sun, and it got badly blanched and yellowed (left). But not all burn color changes are irreversible and the plant has amazingly 'healed' a lot of its burns and is slowly regreening its leaves (not that visible yet in this photo on right, but it's nearly all green now).
This was a nice Gymnocalycium ochoterenae, blooming on the left. It was doing well until late summer when it got really hot. Not knowing that many cacti do NOT like full, hot sun, I assumed this color change to orange was normal. However, soon to follow was the permanent burn below, and soon after, it rotted.
Not all cacti respond the same way to the horrible stress of burning. Left is a Matucana, which fried, and died. Right is a Gymnocalycium which fried to a sickly orange color, but then somehow healed itself (see below).
Slowly its color began to return (left) and it even flowered, and finally only one spot on its side remained scarred (right). Eventually it become completely green and normal looking before I let it rot from too little sun (a few years later... oh well).
The colors of necrosis and rot. There is a sickly green-brown to yellow-brown color that corresponds with a mushy texture that is every succulent collector's nightmare. More often than not, it signifies the end of the plant due to fungus and rot, often too late to do anything about it. Black is generally another bad color and is often associated with necrosis (dead tissues), another often abnormal and bad color change. However not all black is hopeless, and sometimes it can a normal progression of stress. Dead brown and black colors are easily recognizable, but if only on just a part of the plant, do not necessarily equate to the colors of doom. And if the brown or black/green line is distinct, this is actually a good thing in terms of overall survival as this line demarcates a clear border between life and death, with death just waiting for one to take a clippers and remove. Many aloes, the spotted ones in particular, tend to normally necrose their leaf tips but there is always that sharp margin of brown/green so you can tell the healthy green parts are still safe (unlike the less clear demarcations one sees with that soft, gooey yellowy-brown color change).
Colors of necrosis and death (Aloe broomii left) and some cactus I can't even remember right)
Before I realized my climate is not a good one for most Sempervivums, I happily planted them in a nice community bowl (left) and sadly watched in horror as the summer heat wave changed them all to the same color (first to green, then to pale brown, then to mush). This is stress gone too far.
The dark brown colors of these Euphorbias (left) and the giant Cereus (right) are NOT normal, and signify death, and probably from rotting
These Pilosocereus photos show a nice clump of cacti I had that went through a particularly cold winter day. Black spots of major tissue stress (necrosis) began to show, and the over all plants showed an interesting but gruesome array of necrotic color changes (right) that all ended in a big oozy pile of yellow-brown mush.
Shape change. Some plants will change their shape with stress, notably from excessive heat and sunlight. Some aloes, for example, will literally cover themselves up in extreme situations, basically protecting the sensitive center where the growing meristem is. Others, as mentioned above, just necrose away the tips, or even sometimes nearly their entire leaves to conserve moisture during periods of extreme drought or heat. These tips will usually grow back once it cools down or rains. This is certainly not unique to aloes, but since I know mostly aloes, those are the plants I see do this most often. These changes are also considered normal signs of stress.
These two Aloes (Aloe cryptopoda left and Aloe glauca right) are showing a typical response to high heat, full sun and dehydration, curling their leaves over the meristem. The leaves will reopen into a normal rosette shape once it rains a few times, or cools off for a while
Aloe peglarae is particularly well adapted to hot sun and high heat, not only with its blue coloration, but also its ability to curl nearly into a ball (left), and then reopen and revert to blue (right) when winter comes
Another popular and stress-affected Aloe is Aloe aristata, shown in the four photos above (hot and dehydrated in the left photos, and cooler and well watered in the right photos)
Aeonium arboreum 'Zwartkop' is one of the most amazing and striking succulents in my garden... in winter. But in the 110F summers, it looks like the photo on the right. No, it is not dying, really, but severely stressed. However, it will quickly return to is glorious black on the left once it cools down (watering these often does not help that much, but I do it anyway- they still curl in the heat).
Aeonium 'Cyclops' is another great garden succulent, and it changes in appearance along with the seasons (two photos above), but looks terrible in August (left, lower photo) when the blistering sun ravages it. This stress is handled well, though and it quickly recovers around November sometime.
These Aloe greatheadiis show some color changes with the hot, dry summes, but the most striking thing is their leaf tip necrosis. Some will necrose nearly all the way to the center of the plant, but the new leaves will come in normally as soon as it gets moister and less hot
This is a stress change where one can intervene- regular watering and a bit of full sun protection will keep these spotted green aloes looking fairly normal, even in the heat of the summer if one does not like the look of dead leaf tips
However it will reverse itself, as seen in the Aloe parvibracteatas on the right, which looked like that one on the left just 5 months earlier, assuming the weather changes
Aloes are not the only plants the undergo summer leaf tip necrosis stresses. Dudleya anthonyi (left) and Dudleya candelabrum (right) do this as well
Shriveling. This is a relatively obvious sign of water stress in succulents and sometimes it is not easy to know if the shriveling is normal for a plant or not. That takes some experience and/or experimentation. Initially lack of water probably stimulates a succulent to close all its ‘pores' (called stoma). But eventually this is not enough and the water it the succulent areas of the plant is reduced, leading to shriveling. If normal, this shriveling will reverse itself after water becomes available again. Should water not become available, shriveling is usually followed by leaf loss or more permanent signs of desiccation, and then death, eventually. And some shriveling is just a sign the tissues within are turning to that rotten mush, and the entire plant is on its way to caving in.
These two Crassula ovatas (Jade Plants) are showing classic dehydration stress in late summer by showing shriveled an droopy leaves. The plant pulls the water from the leaves first, I suppose, in these plants, during times of water deprivation. But one good rain will completely reverse this appearance, and the plant is no worse for wear.
Dudleyas albiflora (left) and formosa (right) also show some leaf shrivel as well as leaf loss in response to severe summer stresses of heat and drought.
these leaves are not shriveling in the same way, but folding up, from dehydraton. My experience with aloes is when one does not intervene soon once the plant dries out so much the leaves shrivel, it means near total root loss, and one has to be very careful about slowly rehydrating these aloes or they will quickly rot.
Bowiea volubilis, the Climbing Onion, is a pretty hardy plant, but during extreme summer heat, it too shows stress- see shriveled orbs in photo to right. The texture also changed for hard and smooth to soft and spongy, normally a texture I associate with rot, but so far, no rotting, and it does this every summer
I don't know if these 'twisting' of Ferocacti is always a sign of 'shriveling' in dehydration and this plant is not mine so I am not sure what it normally looks like. But I have had several large Ferocacti with almost no roots that were ornamentally tightly spiraled and somehow still alive (sadly that was before I started photographing plants so I don't have examples of these two in their corkscrew shape). When planted and slowly rewatered the roots came back and the corkscrew shape I liked so much, completely unscrewed itself until the plants fattened up and had perfectly straight up and down rows of spines... healthy plants! But no longer so cool looking. The Melocactus on the right has also showed signs of corkscrewing or shriveling in response to a particularly long, dry period. And the Cereus cactus below was being offered at a nusery for sale. In this case, the stress of dehydration has an appeal and may allow this plant to be sold as a 'spiral' form, when in all liklihood, it will unspiral as soon as it gets some water. I hope this isn't being sold as a rare monstrose form.
Leaf loss. Some plants are simply deciduous when environmental conditions are not right, though this response to stress is usually very familiar to even the most inexperienced of gardeners. What sometimes is not expected is what time of year this deciduous activity occurs. In succulents, particularly ones that don't like excessive heat or lack of water, the deciduous period is in the summer, not the winter as with most of the more common plants people might be familiar with. Some succulents will lose leaves in one climate, but not in another more ideal climate. So sometimes it is hard to classify a plant as deciduous or evergreen as their appearance may depend totally on where they are being grown. I call these plants "potentially deciduous" to describe their ability to deal with stress in an opportunistic way, and not necessarily an obligate one. Though leaf loss is often a normal seasonal stress response, it too can sometimes signify that the plant is on its way out.
Cyphostema juttae in above three photos: upper left summer, upper right, New Years, and to the left on this level is early spring plant completely and totally normally leafless
Euphorbia compactum (aka Synadenium grantii), or Dead Man's Tree, is an 'opportunisticly deciduous' plant, losing its leaves (right) in winter only if its exposed to enough cold. If not, it keeps its leaves all year round.
Pachypodium's geayii and lamerei are also variably deciduous, with most winters seeing them losing most if not all their leaves (upper right). But some years only a few plants lose their leaves, as this relatively warm winter last year. Lower left photo shows a Pachypodium lamerei still leafy in April while the Pachypodium geayii next to it has lost all (mostly) of its leaves. All 'normal' but adaptive (to my abnormal climate) stress responses. Many Pachypodium geayii lose leaves in dry season in Madagascar, but Pachypodium lamerei is often leafy year round there (never gets cold enough there).
But some succulents, though still chosing leaf loss as part of their stress strategy, are obviously repsonding to different stresses. This species, Tylecodon cacalioides, is leafless in the SUMMER (upper left), and fully leaved in winter (lower left) with leaves starting to come back in around mid autumn (about when some other plants are doing exactly the opposite). So this leaf loss is more heat or drought related than a cold response.
Here is another succulent, Veltheimia capensis, or Sand Lily, (a bulb) on the opposite schedule, too, fully leafed out and flowering during the rainy winter (left) and just coming out of its summer dried up funk (right) in September
Though one usually associates flowering with signs of good health and lack of stress in most plants, some plants will only flower if they have been sufficiently stressed out. Good examples of this are the Christmas, Thanksgiving and Easter cacti (Schlumbergeras and Hatioras). If kept in an ideal tropical environment with plenty of warmth and light throughout the year, these plants will happily grow and stay healthy... but rarely flower. And the flowering extravaganzas they go through are usually the entire point of owning these plants as they are far less interesting in their vegetative states. These all need a period of increased darkness and cooling off (I am not saying those changes are severe stressors, but they are changes away from the ideal) to be stimulated to flower well.
Without some stress, we wouldn't get to see nice explosions of flowers from these Christmas cacti
Dormancy. This is not necessarily a physical change, but a growing change, or change in the ‘action' of the plant. Many succulents go dormant in times of stress (heat or cold etc.) and that may be the only sign there is that the plant is stressed (unless one bothers to dig the plant up and notice there are little or no roots left). Most cacti go dormant in winters yet look exactly the same as they did in summer. On the other hand a lot of succulents are dormant in summers. I notice that my Haworthias are often static in summers, and if I mess with them any, they sometimes tend to fall over since their roots often shrivel and sometimes completely disappear, allowing the plant to be dislodged at the slightest touch. Yet the leaves look the same as ever. These are stressed individuals but they do look pretty much the same as they did in other times of the year. I find the most of the time the cooler weather and early fall rains bring most of these coma-like plants around again and they re-secure themselves to the soil with their new roots and start to grow again.
Dioscorea macrostachys is a frustrating plant for me, as sometimes it just sits there. Sometimes that means conditions are not right for it crank out one of its vines... or sometimes it means it's dead or rotting. Dormancy that lasts too long should raise one's suspicions and the plant should be uprooted to make sure things are OK down below soil level.
Cycads are particularly frustrating, too, as they go dormant for extended periods seemingly regardless of seasonal variation. This Dioon edule on the left was moved and the leaves cut off for the move, but no hint or signs that this stress is letting up has occured in a long time. It is still alive assured by its firmness, but otherwise how would one know? The Euphorbia horrida major on the right is certainly alive, but I have had this plant for over 2 years and it has not grown an inch. What is stressing this one out I don't know.Succulents often live in tough climates where they are exposed to intense environmental changes. These plants have evolved to deal with these stresses and sometimes quite remarkably, and even beautifully. Though I hesitate to say that stress is a good thing in these plants, I can at least say that it is not always a bad thing. And I would urge those that grow these plants not to stress out about them too much. We humans just don't seem quite as well-adapted to stress as our succulents.