Lemaireocereus are, on the whole, difficult plants for beginners and require rather more warmth in the winter than most other cacti and succulents. They appear to be extremely susceptible to rhizoctonia. the fungus which attacks the soft collar of a plant's stem where the main body of the plant meets the compost. Systemic fungicides such as benomyl can give some help here and it may be a good idea to drench the plant with a solution of water and benomyl in the proportions recommended by the manufacturers with the last two waterings being given in September. Lemai-reocerei generally form tall, branching clumps in their native habitat although Lemaireocereus liumilis forms a dense low-growing thicket. The flowers are only produced on older plants and, with the possible exception of L.lhurberi (the organ pipe cactus), are generally rather slow growing.
Lemaireocereus aragonii is one of the most handsome species whose dark green stems bear pronounced glaucous bands at the point where each year's fresh growth has been made. The ribs are very large and form a feature of the plant being between six and eight in number. It is, unfortunately, rather slow growing in cultivation which is curious since, in its native Costa Rica, the plant is extensively used as a hedging plant. In order to preserve the glaucous tinting of the stems it is best to apply water to the roots from underneath, either standing the pot in a saucer of water if this is possible, or growing it on a bed of sand which can be moistened as necessary. Not only does this help to preserve the bluish tinge of the plant but it also helps to prevent the c of the collar rot caused by rhizoctonia and mentioned earlier.
Lemaireocereus marginaius is now frequently referred to as Marginalocereus marginaius but it is included here because many nurserymen still sell it under the older name. It is widely planted in Mexico (where it is also native) on account of its very decorative stems. The dark green slender stems with five or six ribs are highlighted by the areoles which are so closely set together as to appear almost continuous down the side of the ribs, and which are tilled with brilliant while wool. The young growth is made even more spectacular by the red tinge on the juvenile spines. Like the preceding species this plant is widely used as a hedge and because of its upright habit it makes an almost impenetrable barrier when mature. It is slightly faster growing than the preceding species, but similar care should be exercised when watering it. and it needs a warm dry atmosphere during winter.
Lemaireocereus pruinosus is another plant frequently found but it appears lo be more delicate than the others and more difficult to overwinter. It has five or six very pronounced ribs with few spines on them, the areoles are closely set. and the young growth near ihe apex of the plant has a dense hoary grey frosting. L. eburneus is also sometimes sold as L. griseus and is similar to the preceding species but has between eight and ten ribs and rather less 'frosting' on the young growth. The fruits, which are, of course, only produced on much older plants, are delicious and it is consequently widely grown throughout South America. The plant has other values besides its fruit. It is used in Curaçao for hedging and in Venezuela it is used by the Indians in the construction of their houses, in rather the same fashion as lath and plaster were formerly used in Britain, the split open sections of the stem forming the laths to which the mortar and tiles could subse-quently'be attached. The branches are also thick and fleshy enough to be used as a vegetable in Curaçao.
Other species of Lemaireocereus frequently offered for sale are L.chichipe, whose areoles are set deep into the ribs, as opposed to L. pruinosus where the areoles are bome on top of the ribs, and L. chende which is similar but has between seven and nine ribs, whereas L. pruinosus has between nine and twelve.
Continue reading here: Machaerocereus
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