Menu wiki

Table des matières

Outils pour utilisateurs
Sponsor du CF
10 et 11 juin 2023
Fête des plantes du domaine de Péré (Prissé la Charrière, 79, France)
J'y vais
10 et 11 juin 2023
ACS (Bédée, 35, France)
J'y vais
2 et 3 septembre 2023
Les Journées des Plantes de Guerlesquin (Guerlesquin, 29, France)
J'y vais
3 septembre 2023
Journée des plantes d'Uzès (Uzès, 30, France)
J'y vais
8, 9 et 10 septembre 2023
ELK (Blankenberge, Belgique)
J'y vais
15, 16 et 17 septembre 2023
Festa del cactus (San Lazzaro di Savena, Italie)
J'y vais
Toutes les dates

(Version française sur la page FAQ - questions fréquentes)

My cactus is rotting at its base, what can I do to save it?

If it really is rot, it is urgent to do something. However, in ageing, it is possible that the plant becomes woody; that is normal. To tell the difference, touch the base and see if it is hard or flabby. Hard means, no problem. In the second case, it is rot and the plant must be treated with care. Using a sharp knife, make a clean cut to take off all of the infected part. When no more red is visible, disinfect the knife and cut off a last slice. Note that if white liquid pours out, the plant is not a cactus but an euphorbia. In that case, be careful! If the liquid comes into contact with sensitive places like eyes, mouth, etc. youmay be harmed. It is toxic ! To stop this white liquid to pour out, dump it in water. The wound has to be allowed to dry and to heal for 2 to 3 weeks for a small pant, for 2 to 3 months for a tall one (over 1 m.). Put it in a light place but without direct sunlight, free from draught. Prepare a pot filled with soil for cacti and a stake. Put the plant here on, held upright with the stake, without burying the base for more than 1 cm. From time to time moisture the soil until the plants starts to grow again. Then you can water as usually.

The colour of my cactus changes. It was nice green, and the new growth is pale green. What to do?

Probably, your cactus suffers from lack of light. Change its place and put it in a spot where it will get much more light. Avoid direct sun, or allow it to get used to more light progressively, otherwise the plant is at risk of being burned. (truly, even cacti are sensitive to insolation, but they are able to be accommodated to it).\ If there is not a lack of light, it might be a shortage of mineral elements. The easiest thing to do then is to repot your cactus in fresh soil, taking off as much as is possible of the old soil. Remember ! A freshly repotted cactus does not need fertilizer for the firsts few months or so, and up to the first year.

For years and years, I am searching for a way to make my cacti grow larger and thicker. Most of my cacti grow "in pride" (as my mother says), there must be some secret... What is it?

If your cactus grows higher than it should, that probably means a lack of light. If the new growth is pale green and thinner than its base, that should be the correct diagnostic. Cacti and other succulent plants need lots and lots of light (not necessarily direct sun). Another point is that a plant grown in open air, outdoors, will be stronger and bigger.

How to get in touch with other enthusiasts in my area?

You have various possibilities: Write an ad (its free) on the site of Cactus Francophone. It works ! I had positive return comments, so why not give it a try!

  • Become member of a society, and then contact the other members of that society.

How to collect the very fine seeds, looking like dust, i. e. those of sedums?

Try this one, which works for many species: use a piece of gauze, like those used in medicine. You can easily find it in a drugstore. It is a very light fabric allowing ventilation and light going through. At the end of the flowering, surround it with gauze and wait for the seeds to be set free. Once all is dry, just pull it off. You may also use a seed pump.

What is the Latin name of the Yucca most currently found in commerce?

It is Yucca elephantipes.

How to get an Epiphyllum to flower?

To flower correctly, Epiphyllums should be allowed a winter rest at a temperature between 6° C and 12° C. In general, their rest period is situated from mid-November until mid-February. However, during this period their soil (2/3 earth + 1/3 perlite or sand or pouzzolane) is to be kept slightly moistened but not sodden. As soon as flower buttons appear, water with an addition of a fertilizer of low nitrogen contentrations but rich in phosphorus and potassium and trace elements.\ After the flowering period, allow the plant to rest for 2 to 3 weeks reducing the watering and place it in a shady spot. In summer a bright spot without direct sun will be perfectly suitable (under a tree for instance). Water and fertilize all summer long and allow the soil to dry out a little between 2 waterings. Beware of water that is too chalky. Epiphyllums do not like this type of water. In case of high pH, a few drops of lemon juice will reduce the pH value.

How to graft the "head" of my cactus that is broken?

It is possible to graft the head back on the stem by performing the classic grafting operation:

  • Cut both parts properly; nice clean cuts are required.
  • Place the head on the stem, slightly push the head by making rounded movements to eliminate bubbles.
  • Keep both parts in close contact. This can be done by means of elastic bands or a string with a “ballast” at either side.
  • Keep the plant free from draught and direct sun for some days.

How do I grow a Pachyphytum oviferum?

Water at the foot of the plant in order avoid to moistening the leaves. Keep it sheltered from rain, or the nice blue bloom will come off ! The plant will grow well too, no problem, but it will be less nice… A trick for multiplication: just one leaf will do !

Last week, I bought a grafted cactus: the foot is upright and green and the graft is yellow with tiny hairs. I presume the yellow cactus has been damaged because its base is rotting; actually the yellow cactus has become glazy and a gluey liquid is pouring out. What can I do to save it?

According to what you ask, the only way to save the plant would be to cut of the healthy (yellow) part and graft it onto another cactus (green). Besides that, unfortunately there is no rescue possible. These coloured cacti are laboratory productions, with little resistance, and they that can live ONLY grafted because they don't have any chlorophyll. In general, they only live some months, maximum up to a year or two.

For 2 years, I have a nice Yucca in my apartment. It seemed to enjoyi its spot and was growing fine. However for about the last three months, its leaves are getting yellow and, above all, they are covered with a kind of white film that is somewhat sticky but that can be whiped off easily, like dust (but it is not dust). What has happened? I can't say it is due to too much watering, on the contrary...

This might be an attack of mealy bugs, small beasts of 1 to 2 cm that live inside their sticky cotton-like fabric. If that is the case:

  • Clean carefully with soap water (Marseillan soap) and a sponge.
  • Use an insecticide spray (Bayer for instance) against mealy bugs
  • Add a systemic insecticide to the watering (for instance Confidor, Laser or Antiofort).

I want a Yucca for outdoors, where can I find one?

These plants often have offsets. At first sight, best would be to find a garden that has one and politely ask the gardener for an offset. Easier is to go to the nearest garden center.

Do I have to take off the faded flowers?

They have to be taken off, but not torn off. Pull slightly to take them off. If they resist, wait for some more days, don't hurt the plant. And do not water on the faded flowers, this risks to rotting. Be sure to water at the base.

What should I use to heal a cactus that I had to cut because it had grown too big?

There is no need to put something on the wound, cacti heal themselves. Just let it dry in a cool dry spot free from direct sun. If the plant is large sized (diameter over 5 cm) let it dry for several weeks. However, some people use wood coal powder or cinnamon. Be careful, some Euphorbia are often confused with cacti. If the cut stem pours out a milk-like liquid, it probably is one of those (take care, the liquid is an irritant). To stop this outflow, pass it through running water. Then treat it like a cactus.

I live in the tropics. To keep my plants at a temperature of 5° C to 10° C for their winter rest, I would have to put my cactus in the fridge, would that harm them?

Yes, they certainly would be harmed by such a treatment. Not only could the contents be kept cool, but the fridge will dry them out as well. Moreover, the transition would be too abrupt. That is unsuitable.

What is the difference between earth and sand?

Earth contains food, but sand only is a support. Consequently, they have to be mixed in order to obtain an open and nourishing soil.

Can white sand of the beach be used in the potting mixture?

No, avoid using sand from the beach because it is salted. Unless you can have it washed by a stream in your garden or by the rain, it will be too salty for your plants. The sand should be large sized, not fine. A size of about 2 mm is perfect.

I have a candle of about 90 cm high, but its base has a diameter much smaller than the top of the plant and therefore, I have to fasten it on a stick and that becomes difficult. Would it be possible to make a cutting at mid-height? Is that not too dangerous for the plant?

You can easily do it if you take some care:

  • Use a very sharp clean knife
  • Make a net, clean cut at a distance from the top of at least 4 times its diameter.
  • Let it dry in a cool dry place, avoiding direct sun. If the diameter is of some centimeters, let it dry at least one month (or two), until it has healed.
  • Place the cutting on fresh mineral soil, held by a stick, without burying it.
  • Wait for the roots to appear before starting careful light watering.

The best time to do it is early spring or the beginning of next year when your plant will be full of water and in full growth.

The young sprouts planted last spring, be prevented left dry over winter?

Actually, young plants are more delicate. If they are smaller than 2 cm in diameter, water them a little bit once a month, enough to enable them to swell up a little bit, but not too much because the soil has to dry rapidly. If the weather is too cold, don't water but wait a few days.

I work in an office and I would like to have a nice small cactus (with flowers because I like colours). It should need little space (we already sit very close in this office) and need little care (mainly because my office is not very sunny).

No problem, the miracle cactus fit for this situation exists: just get a Plasticocactus, any species will do… ;-)

Where can I find Lophophora williamsii?

Lophophora williamsii (=peyote, peyolt) is not at all a rare species, either in nature or in collections. The last time I was at Truffaut, a very wide spread garden center in France, there were Lophophora williamsii available for sale: small plants of about 3 cm in diameter were offered. .

I noticed that there are many more men interested by cacti than women. Is that so? For what reason?

I don't know if that is true, but actually lots of people think so. In general, when a man has such a hobby, he likes to talk about it, whereas a woman would be more discrete? She would prefer growing her plants in her way, without trying to meet other enthusiasts, either neighbours or friends. A man would be more interested in taking part in meetings, travels, assisting enthusiasts' meetings, etc. It is a different approach, but one is not necessarily better than the other. Women prefer to grow their plants for themselves, “in their corner”, whereas men like to be more showy with their colleagues, and therefore are noticed more as collectors.\ This is just an explication, but perhaps there are really more men than women to be interested in cacti…

My plants have mealy bugs, can I leave them on the plants?

No, absolutely not. After a while, the plants stop growing and die. To have nice healthy plants, these small beasts are unfortunately to be exterminated.

I would like to meet other enthusiasts living in my area. Is there some directory? If not, could a record be made?

In whatever area you live, this kind of service does exist. It's the part of enthusiasts' societies like BCSS or CSSA. You can also place a small ad in the corresponding column of the Cactus Francophone. Being a member of the CF, you will have access to its directory where are listed all those who agree to be, selected by country and by department.

How big can a giant cactus grow?

As a real name, the “giant cactus” does not exist. Cacti sizes can vary, according to the species, from some mm or cm up to several meters. The highest “traditional” cacti are the candles that are seen in the “western” films and that can reach up to 23 or 24 m. However, they are largely overtaken by the liana cacti such as Hylocereus whose size only is limited by the size of its host tree. The jungles of Amazonia probably house that kind of cacti measuring 30 or 40 meters long, or may be more.

What is the a field number?

The field number is a code given by the botanists to the species, plants or seeds, that they gather in nature. Most often, it is composed of their initials and a number. Example: SB68 for Ariocarpus retusus collected by Steven Brack, KK176 for Copiapoa cinerascens collected by K. Knize, etc… This code often is transmitted to the descendants of the plants or seeds. For some enthusiasts this is of primary importance, so much so as to make them name their plants as being “KK176” instead of “Copiapoa conerascen”.

What is a succulent plant?

The science called Botany organizes plants according to their relationship with each other. Thus, cacti are plants related to the family (in botanical meaning) of the Cactacae. There are many other families, see also the encyclopaedia of this site.

But it also is possible to organiz plants according to other particulars, for instance “plants with red flowers”, “edible plants”, etc. That leads to a group of plants including species of various families. The succulent plants are this kind of group. They are called succulents because they have a big quantity of “suc” (sap), that is their food stock and water storage. It has nothing to do with any gustative qualities !\

Almost all cacti are succulents (besides Pereskia), but there are numerous succulent plants other than cacti: Sedum (crassulacae family), Lithops (mesembryanthemacae), etc. The encyclopaedia of the site contains some files to tell you more, mainly the family files.

Why are there no cacti with blue flowers?

Plants colours are due to 2 main families of elements: betalaines and anthocyanes. There are other origins of colour, like chrorophyll, but the possibilities are rather limited. Betalaines and Anthocyanes are exclusive to each other, that means that a plant synthesizing anthocyanes cannot synthesise betalaines and vice versa. Most of the plant families use anthocyanes, except the Caryophyllaes, a super-family including beet, but also the mesembryanthemacae and the cacti.\ The cacti's colourings are the betalaines, divided in 2 groups: the betaxanthines (yellow colour) and the betacyanines (red colour). A betalaine of blue colour does not exist (their chemical composition does not allow to give that colour), and so there will never be blue flowering cacti, neither Lithops.\ Certain plants can be found having a tinge close to blue (Wittia amazonica for instance), but the colour (that actually is rather violet) is not due to a colouring but to the structure of the cells at the surface of the flowers.\ alain

I would like to raise a collection of cacti and other succulent plants in an aquarium. Can I do so?

No. Unfortunately that's a very bad idea. The main problem with an aquarium is the ventilation, which is nearly nonexistent. That may be a good thing for some kind of plants, but certainly not for cacti. Cacti and other succulent plants need a rather dry atmosphere, an environment where water can pour out and evaporate very rapidly. Otherwise the risk of rotting is very high.

How can I start a collection?

Lots of people start with plants bought in supermarkets or garden centers. One must start somewhere, but there is a better way: specialised nurseries! Ideally you should go and pay a visit to a producer and choose the plants yourselves. It's a way to see how many different cacti and other succulent plants exist, and meanwhile you can discuss matters with the producer to get some hints. If you live too far away, you may try the “sales by correspondence” way, also existing in this branch. Most producers offer an assorted choice of plants that are easy to grow and are recommended for beginners; that's what we would suggest, for yourself or to offer as a gift.

What should I do with the offsets at the base of my plant: leave them where they are or take them off?

It's up to you.\ It is not necessary to take off the offsets growing at the base of casti. You can leave them where they are without any problem. However, there might be some reasons to takle them off:

  • From an aesthetic point of view: if the offsets grow in an untidy manner, or if you prefer a solitary plant, you can take them off all or some of them.
  • Multiplication: growing the offsets as independent plants is a good way to multiply a plant. See the growing advice to learn how to do it.

The only possible risk of maintaining all the offsets on a plant might appear on very large sized clumps, with tens or hundreds of heads. In that case, after a watering, moisture may stay for a longer time around the collar of the plant, because its volume will slow down the evaporation. This risk is nonexistent with small plants (less than 20 cm in diameter).

How long will needs seeds to germinate?

That's very variable according to the species. Under the best conditions (see growing advice and the articles), it may take some days, or even just some hours for the fastest (Astrophytum) up to some months or some years for the slowest (Opuntia, Thephrocactus). For most species, germination will start after 4 or 5 days. After 2 to 3 weeks, you may consider that everything that could germinate has really done so.\ alain

How can I prevent my cat eating my plants?

Easy: just powder some pepper around your plants, especially at their base. Your cat will no come near your plants after that!\ patrick91

Will all cactus flowers give a fruit?

All cactus flowers will turn into a fruit with seeds if they have been correctly pollinated.

  • Some, the auto-steriles, will need the pollen from another plant. This other plant must be from the same species, or from a near one in case of hybrid production. This other plant must not be a cutting from the first one.
  • Others, the auto-fertiles, do not need another plant to bring the pollen. They can accept their own pollen, however the pollen from another plant will ususally produce better seeds, and more.

In this last group, some species requires an external action (insect, human with brush, etc.). Some can produce the fruit by themselves, such as Setiechinospis or Frailea. Frailea flowers can even stay closed and produce a fruit!\ \ For some plants, such as Echinopsis (broad view), Parodia (idem), Eriosyce (idem), Gymnocalycium, Astrophytum, Thelocactus… and others, it is easy to spott a fruit or not. Either the flower dries but the bottom part gets biggers and transforms into a fruit, or everything dries and falls off.\ For others, such as Copiapoa, or some Mammillaria, … the fruit formation is not easily spotted.\ For a last category, the fruit formation is so shy that it appears only when mature (Ariocarpus, Epithelantha, some Mammillaria…) or worse when the plant dies or when you cut it, the fruit being inside the plant body (Mammillaria theresae or pectinifera).\ alain

Which cactus can block the "harmful waves" from screens?

It is said that putting a very specific cactus (Cereus hildmannianus ssp. uruguayanus with 6 ribs, usually sold under the wrong name Cereus peruvianus) would block the “harmful waves” emitted by the computer or television screens. Obviously, this is false, like all that seems too beautiful to be true. If it is true that any matter blocks at least certain waves (and we are still wondering which “harmful waves” would need to be blocked), this matter must be placed between the object which emits the waves, and the object to protect. To place a wall of cacti between you and your screen will probably stop many things, in particular the light waves… so just turn off the screen as in any case you will not see anything anymore.\ yann

Why the areoles of my cactus are becoming black? What is this fungi developping there?

The fumagine come from fungi belonging to several species: Capnodium meridionale, Capnodium oleae, Ceratocarpia cactorum… etc. These fungi proliferates from the sugars contained in the honeydews of insects: Cicadelles, Aleurodes, Plant louses and other mealy bugs. In the case of Ferocactus, Thelocactus and some others, the plants themselves produce this honeydew by the glands on the areoles and sometimes confused with very young floral buttons. To develop, the fumagine needs favorable climatic conditions: soft temperatures and moisture.
The fumagine does not attack the plants, it does not penetrate inside its skin. But in great quantity it blocks the light, preventing photosynthesis and gaseous exchange. Moreover, it gives a disgusting aspect.
To remove it, There is no miracle solution and it will be necessary to start again the following year. One can clean the plant with a small brush and a deterging product containing a little bleach. Tke care to rinse a lot. To avoid such problems, one can treat his plants with a copper-based antifongique. They will not be black any more… but blue.\ alain


Author's name is indicated for each faq, or Yann
Translation : Willy and Yann