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Along with other articles, columns and club updates, each monthly issue of the Henry Shaw Cactus Digest includes an article or two on members' favorite cactus and succulent species. The articles typically include photos and facts on the plants' natural origins and distribution, growing conditions, common and scientific names, care and cultivation tips, and helpful hints for encouraging flower production.
Follow the links below this month's offering(s) to enjoy previous Plants of the Month or click to read a sample of the HSCSS Digest in PDF format.
May 2017 -- Stapelia
By Bob Williams
Everyone has faced this problem. You have houseguests who just won't leave, but you're too good a host. You may have family visiting from out of town, and they have decided to stay a few extra weeks because you have very comfortable beds.
You have tried everything: turning the hot water heater off, turning the furnace off if it's winter or the air conditioner if it's summer. Nothing is working. Fear not. There is a solution. Keep a supply of flowering stapelias on hand.
Use them as a centerpiece on the dining room table. Place a few in the guest bedroom. Problem solved! You have brought out nature's secret weapon -- the carrion plant.
Stapelia is a genus found in the Apocynaceae family. At one time, Stapelia was included in the genus Obrea. In 1975, Stapelia was separated from Obrea and has remained so ever since.
The name Stapelia was given by Carl Linnaeus, who first described it in 1737. The name honors Johannes van Stapel, a 17th-century physician and botanist.
There are between 50 and 80 species of Stapelia found in the wild, depending on the source. Stapelias are native to the arid regions of tropical and southern Africa, and are found in Botswana, Zimbabwe and especially in Namibia and South Africa, where about 45 species are found. Outside this region, they are also found in southern Angola, northern Zambia, southern Malawi and central Mozambique.
They grow in clumps that can reach 3 feet in diameter. In the wild, they are found growing under shrubs or in well-shaded areas. While they can withstand direct sunlight, the light causes the stems to have a reddish hue. In any given area in the wild, they are not very abundant and have been known to disappear in areas that have had populations for years.
Stapelia stems are soft and fleshy. They are four-sided or quadrangular. Depending on the species, they can grow to 6 inches tall and 2 inches thick. The small ones may be 1/4 inch wide and 1 inch tall. The branches form from the bases of the plants. This is how they form such wide clumps.
Stapelias are not grown for the beauty of the plants. They are grown for their flowers. Stapelias have unusual five-lobed flowers that can be red, maroon, purple or yellow, often with interesting banded patterns. The flower surfaces can be brightly polished or matted with hairs.
Flowering occurs in the late summer or early fall. The flowers do not last very long, a few days at most. Most clumps send out multiple flower stalks, so a plant can be in bloom for a week or more.
The granddaddy of all stapelias is S. gigantia. The petals of its flowers are a muted yellow and can reach 12 inches across. S. hirsute is another species, with a flower reaching 7 inches across. At the other end of the spectrum is S. scitula. This plant only grows to 2 inches tall. The stems are only 1/4 inches wide, and its small, deep purple flowers may reach only 1 inch across.
Besides the flowers, there is the smell. These plants have the odor of rotting flesh -- hence the nickname carrion flower. The odor is meant to attract flies, and if you have ever had one of these in bloom, you know it works. It has been reported that flies are sometimes so deceived by the odor that they lay their eggs on the flowers.
Stapelias are easy to grow, but it can be hard to keep a clump looking good. As the clumps increase in size, the innermost branches tend to die off, leaving a "hole" in the middle. They need a very well-draining soil mix and do better in clay pots instead of glazed ones. If you overwater, rot is swift to come, and you end up with a gooey mess.
Stapelias can take full sun, but do better in bright, indirect light. They can handle high temperatures, but not cold. In winter, they should be in a room that stays above 50 degrees. Watering should be slowed down during the winter, but not eliminated. A small amount every three weeks works. These plants are not winter-hardy in the St. Louis area. In zone 9-10, they are commonly used as landscape plants in rock gardens, as the clumps will cascade over a rock ledge.
If your plant flowers, and germination occurs -- and you can stand the smell -- you can propagate the plants from seeds. The only drawback is that the seeds take almost a year to ripen. Once ripe, germination is fast.
An easier way to propagate is by taking cuttings. Cut a branch with a sharp knife and let the cutting heal for about a week. Then place the cutting in your starting mix. Water carefully to prevent rot.
Sometimes a branch in a clump starts sending out air roots. When this occurs, cut the branch from the base of the plant. Let the cutting heal and plant the branch so the air roots are below soil level.
Wooly aphids and mealy bugs find these plants a favorite source of nourishment. Frequent inspections should be done.
There are many varieties of Stapelia available on the Internet from many different sources. As you shop, consider the plants' many attributes: fly attractor, guest repellent and the biggest flowers you may ever own.
May 2017 -- Pilosocereus purpureus
By Betty Gravlin
Pilosocereus is a genus of cacti distributed throughout Mexico, the Caribbean and Brazil. They are upright with relatively thin stems. In cultivation, they mostly are grown in greenhouses because of their size and need for warmth in the winter.
The Pilosocereus name derives from the Latin for "hairy cereus," because of their spiny aureoles. Their flowers are shaped like tubes and often blue, and they grow fleshy fruits. Some species grow to a height of up to 30 feet.
The Pilosocereus purpureus cactus that I have is a single green column. It has 11 parallel lateral ribs that superficially resemble cephaliums, copious development of wooly, beard-like hairs in the flowering zone and bristles at the tops of the ribs. The column tapers at the top. It has brown and golden spines.
Light: Like most cacti, they need lots of direct sunlight to flourish.
Water: Watering them weekly should be sufficient, although they need a solid supply of water during the summer. Make sure not to overwater them, which can cause rot.
Temperature: Warm tropical temperatures, ideally around and above 70 degrees.
Soil: Pilosocereus plants like a dry soil with some organic material, and good drainage is absolutely essential.
Fertilizer: Complementing their water with a diluted liquid fertilizer once every few weeks during the growing season will help. Use a balanced fertilizer like a 20-20-20 with equal parts nitrogen, phosphorus and potassium.
The best way to propagate pilosocereus plants is by cuttings. You can cut off the top of the plant once it's begun to mature and replant it as the bottom of a new one. This is a good way to produce new plants. Once the top cuts have
rooted, they should flower fairly early in their lives, so cutting off the tops of existing plants is a good way to ensure flowering in your cacti.
These are tree-like, free-standing cacti that are usually too big to be grown in pots. Cacti in containers do benefit from sporadic repotting, though. Lift the plant gently (making sure to protect your hands), knock away old soil and
replace in a larger pot. Make sure not to water the plant for a few weeks while it gets settled in its new container. Keep an eye out for pests like mealy bugs and red spider mites. Water regularly for best results.
CactiGuide.com -- Pilosocereus puppureus Care -- http://cactiguide.com/forum/viewtopic.php?f=25&t=38450
Tips for Growing Pilosocereus Cacti -- https://www.thespruce.com/grow-pilosocereus-cacti-1902966
May 2017 -- Adenium obesum
By Nikki Murdick
Earlier this year, I was the delighted "winner" of a lovely Adenium obesum. This plant has spent the winter happily living in my dining room. It kept most of its leaves throughout the winter, although I think it will be happier still as soon as it can move outside.
This plant, often called the desert rose, can easily be found in plant nurseries or gardening centers. It is considered an easy plant to grow in temperate climates, blooming profusely and living long under good care.
Adenium obesums are noted for their thick stems or caudices with fleshy branches that are usually arranged in a spiral. The leaves are generally oval in shape and vary in size, getting larger with the age of the plant. The blooms are trumpet-shaped and come in different colors, including white and shades of pink and red.
Adenium obesum is in the family Apocynaceae and was first described as a genus in 1819. It has a large distribution: the Arabian Peninsula, including Socotra; tropical and East Africa; and now southeast Asia and the Philippines.
Over time, the number of species in the genus Adenium has been listed as anywhere from five to 12. Currently there are five accepted species: A. obesum (A. arabicum), A. boehmianum (found in Namibia and Angola), A. multiflorum (found from Zambia into Southern Africa), A. oleifolium (found in South Africa, Botswana, and Namibia) and A. swazicum (found in eastern South Africa).
The growing season for Adenium obesum is the spring and summer months. During the hot summer, they may need daily watering. Adenium obesums prefer warm temperatures above 50 degrees F, even at night and during the winter.
The plants can grow from 6 to 10 feet in height, and usually are shaped more like a bush than a tree. Adenium obesum plants grow best in well-drained, sandy or gravelly soil. They prefer direct sun, and it is suggested that the plants be rotated every two to three days to encourage the plants to grow straight, strong stems. Most websites state that this plant needs to be repotted about every two to three years, although it may need to be repotted more often.
Take care when working with this plant if there are small children or animals near, as parts of the plant are poisonous when ingested. The sap contains toxic cardiac glycosides that are said to have been used as arrow poison throughout Africa in hunting large game. Some people also have a reaction from getting the sap on their skin, so hand washing should be done immediately after working with this plant.
A. obesum can be cultivated by seeds or cuttings. In order for the seeds to germinate best, they should be left in the large seed pods until they dry off naturally. To do this, you may need to tie a bag around the seed pods to capture the seeds. Once the seeds are planted, they germinate easily, but require regular watering. Cuttings should be done using clean shears so that possible disease is not spread. Cuttings root easily during the spring and summer growing season.
Adenium obesums are prone to various pest problems. They can host spider mites and especially mealy bugs. The plants should be kept in an area with plenty of moving air, and dead plant debris should be removed immediately. Mealy bugs can be removed with a strong spray of water.
In addition, these plants can be prone to stem rot, although this is less prevalent once the plants have survived their first winter. Root rot can also be a problem, so drainage trays under pots should be emptied immediately after watering.
If you are interested in this plant, you can find more information and photos on the following websites:
Dave's Garden -- http://davesgarden.com/guides/pf/go/527
Desert Tropicals -- http://www.desert-tropicals.com
Home Guides -- http://homeguides.sfgate.com
National Tropical Botanical Garden -- http://www.ntbg.org
Tips for Plants -- http://tipsplants.com/plants/house-plants/adenium#ixzz4bzKxA5CX
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