Adeniums may be propagated by seed, air-layering , cutting and grafting. Other methods have not been tried by the author, but its not to say that they don't work. I have primarily propagated them from seed and made air-layers with ease. I will cover all aspects of propagation and let you decide what's best for you.
Seeds are the best and most successful means of propagation. Variations occur in seedlings even when siling crossed. But most of us want something different than what we already have, so this is not such a bad means to get more plants. Many of us get seed pods periodically from time to time. But knowing when they ripen or mature is sometimes tricky. I have used old vegetable twist-ties wrapped around larger maturing pods with excellent results. This way, we can allow ourselves freedom from an unexpected burst and loss of seeds. This method will allow us to ripen seed safely and get a better germination ration then picking them too early or too late. Just wrap each pod with a twist-tie several times around from one end to the other. This way, when the pods naturally ripen, all the contents are still gathered and unfurled without the wind blowing away valuable seeds. See photo illustration of seedpod protection
The planting of the seed just requires that the soil be sterile (straight from the bag, and not previously used) and well draining. I have used any one or a mixture of the following ingredients; peat moss, perlite, vermiculite, pumice, potting soil, redwood composts, sand, etc. Use a 10-15cm diameter pot that is wider than deep (either a bulb pan or azalea pot). Plant all the seeds in a community-pot fashion and allow seeds to lay on the surface. Mist or lightly sprinkle seeds and media so that excess water runs out from the bottom. Cover the pot with a plastic wrap or clear plastic saucer and allow to sit where it will receive intermittent or filtered light. Growing under lights is an excellent way to germinate them as well. Seeds should germinate in 1-2 weeks. Some seeds take a bit longer to develop and may require a bit more time to sprout. Patience is the key to success here. After seeds have produced its first true leaves, remove the lid/wrap and slowly adjust the seedlings to more light and drier air. Keeping the plants misted every chance you get will help. As soon as the next set of leaves appear, transplant them to individual pots (5 cm size is ideal), use a well draining mix with more water holding ingredients to keep them evenly moist. Fertilizing with a dilute soluble fertilizer is advisable now at half strength. Alternate feeding with plain tap water to keep growth even and plants from accumulating too much salts at an early age. As soon as plants fill their pots they should require repotting. Transplant them to the next size pot (do not over pot, just gradually move them up a size at a time) and treat them as regular plants following instructions under cultural practices.See photo illustration of a crowded community pot
This method has yielded many exact replicas of ideal characteristic plant material. Its almost 100% effective and can be used on plants that are young to larger established specimens. Even if you are using a large growing specimen to take layers from, they will still grow and get large after time. Some people have the notion that taking air-layers from large plants will keep them small, since they grow so slowly after getting specimen size. It is very important to keep these air-layers actively growing from removal to establishing their next pot size. I suggest that air-layers be made in spring when the longer days and that you can get some good growth out of them before placing them in winter dormancy. This way, you'll get large actively growing plants in the first season, often with buds and blooms already present or soon to be.See photo illustration of an air-layered stem
Start with a stem that has some good leaf growth and stem thickness. Injure the stem area with a knife or scissors, making sure not to get the sap on yourself. Especially avoid the eyes and mouth, as they are quite poisonous. Maybe not enough to kill you, but can make you quite ill. Wash off sap immediately with soap and water and use a baking soda hand scrub to get the sap's chemical out of your skin's pores. I suggest using gloves if you have them. Be sure to let the injury heal and dry itself off before going further. Dust a little rooting hormone in the cut region and then wrap with moist sphagnum moss. The long fiber variety is best. Cover this ball of moss above and below with a heavy black plastic film (like from a heavy garbage bag, etc.), or aluminum foil is also good and its advisable to cover with a plastic film to cover afterwards to seal in moisture. Use twist-ties or other wire to keep balled moss in place. Rewetting moss after it has been set (even a week later too!) will also help ensure better rooting to take place.
Remove the cutting when some roots are evident and pot in a well draining, higher moisture content soil mix in a filtered light area to get them established in their new location. Covering the soil surface with a heavier media (like gravel, heavy aggregates) will keep a top-heavy plant from unpotting itself if jostled by wind or movement. Water them and allow soil to dry just slightly in between heavy watering cycles. Fertilize dilutely at first then gradually to normal strength, later. Set root-established plants in stronger light as plants start to send out new growths. Treat them as regular plants once they have become established. Be sure to tag all your layered plants so that you know the duplicates from the original. I have seen collections where both seedlings and layered plants grow side by side with no tags and they don't know what they are until a flower is evident. Start early with tagging your collection.
Cuttings are somewhat more difficult to start due to some common fungal and bacterial diseases. Some growers swear by cutting grown plants, while others say its difficult. The important factor is keeping cuts clean and well sealed/cured before placing in a rooting media. I often use a good commercial rooting compound that has a fungicide in it to help prevent root-rot. It is important to keep the soil evenly moist (not wet) and allow good air ventilation through pores in the media. I like to use a mixture of perlite, vermiculite and pumice. Once roots are started, they may be uprooted and placed in a regular potting mix and treated like a regular plant afterwards. Keep cuttings somewhat most when setting out into its new soil and lightly soak with a dilute vitamin B solution and a soil fungicide if rot root is a problem in your area. Its best to start cuttings during the warmer periods of the year (like late spring, early summer) when the warmer months to come will set up better growing conditions for your starts. Make cuttings about 4=7 inches and with a single stem tip cuts for best results. larger pieces will root, but establishing may take a long time and cuts often just sit and do nothing for months before getting established, so start them off as a smaller unit. Make cuttings after the flowers have bloomed on the desired stem cuts. This way all the limited stored food goes to growth and not early flowers.
Grafting is a good method when you receive unrooted cuttings in the mail or are uncertain about how long a cutting has been just sitting in a box. Grafting is quite successful if you practice your grafts to be made easily and quickly. Grafting is also a bit hazardous due to the sap overflow and working with gloves is a bit tedious (like unwrapping a stick of gum with gloves on). Adeniums can also be grafted successfully onto Oleanders as they are faster growing and make new starts quickly. The disadvantage is the you lose the swollen base. But don't think like this, as air-layering made from an established plant can replace it with a caudexed plant later. Also a grafted plant on Oleander can also be buried deeper and hide the thin Oleander stem, just exposing the swollen stem above. I like to graft as close to the base as possible. Choose a stock plant that does not have a well developed caudex or too many branches. Usually a thin stemmed plant works best. Make a cut about two to three inches above the soil line and get your select top plant set aside and ready for transfer. Cut a shallow cleft down the middle of the trunk and make a reverse shaped cut (like slicing either side of the stem to make a wedge) which will fit into the groove and can be held in place without too much excess either side of each plant. Use a plastic wrap, like plastic-tape, or even waxed plastic film and make several layers of wrap to secure top section from falling out of wedge. You may also use a grafting spray to seal in moisture and make it unattractive to borers and diseases. Keep plants out of direct sunlight and wind until new growth starts. When plants have become established, slowly remove wrap and expose trunk to the air. Be sure that stem is securely in place before removing wrap. Some plants will just grow out of their wrap when established, so it can be left on until it it falls off from deterioration. again, I can never stress the importance of labeling. A date of the graft as well as name from your plant should be included on the tag. Plants usually start blooming in their next respective season. So this is probably the fastest method to see flowering plants from cuttings. A photographic step by step will be inserted eventually.