If you would like to submit information to this page, please send an e-mail to
The Sun Burned Cacti
Cacti live in some of the most diverse and hostile environments on earth and have adaptations that enable them to
survive under these circumstances. Most of us have an idea of cacti sustaining themselves in the sun scorched desert
environments of the deserts of North and South America. The fact is that cacti are found in a variety of different
climates, from tropical shade loving cacti like Epiphyllums and Rhipasalis to the drought hardy Copiapoas of the
Atacama Desert in Chile who subsist mainly on the moisture from ocean fogs and every habitat in between.
The problem many of us have is that we collect cacti that are genetically designed the live in these varied climates
with a wide range of light, water, and temperature needs and expect them to live and thrive in locales that are not
The ideal environment for a cactus is not of course solely dependant on its genetic predispositions. There are several
factors that contribute to how well or not well a particular cactus will do under certain conditions. The first
factor is how it was raised before you acquired it. Most of the cacti we purchase where probably grown in a
greenhouse where conditions are more or less kept within a particular range of light, heat, moisture. Seedlings are
kept cooler and in higher humidity conditions with a more limited amount of light than your standard commercial greenhouse.
As the plants grow larger they will be moved into a greenhouse where they receive light through opaque plastic and
depending on the location of the nursery probably a much hotter and drier climate.
So now you've bought your new little pride and joy from your local nursery, cactus farm, or for some of you mail order nursery.
You take it home and immediately place it outside in the hot July sun; probably not a good idea. I have made this mistake
a number of times now. On occasion I have traveled to Tucson and purchased cacti at any of the number of world class
nurseries in the area. I brought them home to Southern California and put them out on my shelf or deck in direct sunlight.
My thinking was originally that these plants were raised in the hot and dry desert of Tucson and should do just fine outside
in a slightly cooler climate outside. How wrong I was on a number of occasions. The problem was that even though these plants
had been living a greenhouse that in the middle of summer probably reached 115 degrees Fahrenheit they still did not receive
any direct sunlight through the opaque plastic of the greenhouse walls. My newly found selections were burning up in the direct
sun at home when it was only 90 degrees. Their skins where burning and turning white and soft. They were literally cooking in
the direct sunlight. To the lack of shade their chlorophyll was breaking down under the intense sunlight.
I have also had the same experience with cacti that were raised outdoors or in a greenhouse, but lived for a year or more indoors
on a windowsill in an air conditioned room. In that year of climate controlled bliss they quickly lost their ability to deal
with the stresses of heat and direct sunlight and they too seemed to become susceptible to sun burn when placed outside.
Some cacti have different ways to deal with strong sunlight and heat. For example I have noticed that the Ferocacti of the
Southwestern Deserts of the United States develop much more abundant radial spines than the same types of cacti raised in
a covered greenhouse. The also will usually have developed better protection and a general hardiness on the south facing
side of the plant. Another example of protection from sun would be a cactus increasing the amount of fur it produces.
(Ex. 3) Some cacti have fur and or an excess
of spines in the area where sensitive new growth occurs which helps shield
the tender new growth form the effects of the sun. (Ex. 4)
Another style of sun and heat protection would be that of a
cactus retreating into the ground to get away from the sun. A classic example of this would be the Ariocarpus Fissuratus
of the Big Bend area in Texas and Mexico whose appearance looks remarkably different in the wild than those grown in a
greenhouse. Example 5 shows an Ariocarpus in habitat, example 6 is an Ariocarpus raised in much more favorable conditions.
Ex. 6*) Personally I have seen these
changes in two particular cacti that I have in my collection. First one is
a Mammillaria plumosa that looked fluffier and fuller when I brought it home.
(Ex. 7) Then after being placed in the
direct sun for several months it became much more withdrawn and the tubercles seems to tighten in on the body making
it very hard to see any of the green of the body. (Ex. 8)
The second example is a Mammillaria haageana that looked
quite normal and vibrant when I bought it. (Ex. 9) After more than a year in the sun it shrank down in size and developed
a much denser amount of spines. (Ex. 10)
So the problem is not that some cacti do not have defensive features for extreme heat and sunlight it is that the
slow growing nature of cacti makes them susceptible to being placed suddenly in unfamiliar conditions. Your
average house plant or tree is able to produce more shade leaves when there is an increase in sun intensity or
in if placed in an area with a lack of sunlight shed excess leaves rather easily. A cactus on the other hand is
just not able to produce more spines, fur, or toughen its epidermis fast enough to deal with a sudden changes in climate.
In conclusion my advice is to know and pay attention to the conditions your cacti have been in and are in. If you are
bringing your cacti out from inside after the winter care should be taken to introduce them to the direct sun gradually.
The easiest thing to do would be to use a shade cloth, though I feel in most climates this isn't necessary early on in
the spring. It would be better to physically move your plants around alternating them in and out of sun from day to day.
For some of us this may be easier than others. In my case I have most all of my cacti on a large shelving unit.
Certain parts of the shelf receive more or less sun during particular times of day. So what I am able to do is alternately
move them around on the shelves depending on what I feel their light requirements are. Also in the middle of summer
when the sun is at its most intense I almost always at least in part cover my plants with shade cloth. Cacti aren't
able to move or put on sun screen so they may need our help when dealing with the elements. So don't let the sun be
an enemy of your cacti.