If there is a “most polarizing species” when it comes to garden-worthy plant selections, Natal plum (Carissa macrocarpa) might be it. Some gardeners love it and some feel precisely the opposite about it. It shows lush green foliage throughout the year, fragrant white flowers in spring and summer, as well as deep red, edible fruit in fall and winter. A bonus is its drought tolerance. Once it has been growing for a year or two, it may as well be a cactus for all the water it requires. And it does not need fertilizer either.
Yet some gardeners find natal plum to be annoying, if not positively standoffish. The first issue is its two-pronged thorns, highly irregular among thorny plants. You may want to get close but the thorns convey a message of “No, I want to be left alone.” These thorns are actually an asset, however, should you be thinking in terms of property protection since Natal plum may grow up to 12 feet tall, making a row of them serve admirably as a living security fence. Some people may not be aware than there are compact, dwarf, and creeping Natal plum cultivars that are highly ornamental, require only occasional, if any pruning, hide their thorns rather well, and do a great job of deterring neighborhood pets from encroaching on your garden space.
Creeping Natal plum photo by Joshua Siskin
The other knock against Natal plum is its white latex sap. Some people find it problematic because it’s prone to send out long shoots in all directions that beg to be pruned, but you would be advised to do your snipping in a dilapidated long-sleeved shirt and gloves. The sap is mildly dermatitc for some people and it will also stain your clothes. There is also an objection that consumption of the fruit is accompanied by some latex sap ingestion, but the same is true of eating figs, that are similarly flecked with latex, so there is nothing to worry about here, as long as the fruit is ripe.
Natal plum is named for the region in South Africa that it calls home. Its scientific name, Carissa, has nothing to do with the girl’s name but is instead the Sanskrit word for a related species that is native to India.
The taste of the fruit is sour-sweet and has been compared to that of a cranberry. Like a fig, you can eat the entire fruit, skin and seeds included. Should you wish to germinate the seeds, you can do so easily enough. Placed in a well-drained soil mix at a depth which, like most seeds, should be no deeper than the length of the seed, they should germinate in two to four weeks.
Aside from their extremely minimal water requirement, natal plum bears a resemblance to cactus in another way, which involves the formation of callus. In the case of people, a callus is what forms on your feet or hands from constant friction. In the case of plants, callus is healing tissue that forms on cut surfaces. Callus is most familiarly seen after a large tree limb is pruned or broken off. The thick raised growth that occurs on the margins of the cut surface is callus tissue. Do not slather pruning seal on such cuts since it will inhibit callus growth.
If you detach a cactus pad, or a stem from virtually any succulent plant, and lay it on its side, callus will form at the base of the pad or stem, usually within a week, at which point it can be safely inserted into perlite or cactus soil mix or, in the case of fast-draining garden soil, directly into the ground. I say “safely” because callus has anti-fungal properties that protect young cuttings from rotting before they root. I know that many succulents, and geraniums, too, root just fine when their stems are simply broken off and stuck directly into the garden, but for some of the more sensitive succulents, and for geraniums as well, waiting for callus to form on detached stems before inserting them in the ground is a wise measure.
Still, as an extra precaution, you do not want the soil to be overly moist until your callused stems take root. That’s why November is favorable for rooting the detached stems of many succulents and semi-succulent perennials, such as Mexican sage (Salvia leucantha), directly in the ground. Because of shorter and cooler days, watering becomes an afterthought as the soil stays sufficiently moist for cuttings to root, and you will not have to soak the soil – which could invite fungus — since scorching hot days, at this time of year, are uncommon.
If you cut a Natal plum shoot halfway through and let it dangle, still attached to the mother plant, the dangling stem will form callus at its base within two months. When this happens, detach the shoot and insert in into fast-draining soil mix in a container, making sure it is protected from hot sun, and it will root within a month.
Tip of the Week: Richie Locasso, who gardens in Hemet, had seen his pomegranate tree decline to where its blossoms would fall to the ground and no fruit were produced. This year, in the spring, he decided to pollinate by hand and now has a sizeable crop. “Most of the fruit is on the outer lower periphery of the branches,” he wrote, “areas to which I had greatest access and most frequently worked on when I pollinated using a small artist’s paintbrush. The tree was covered with blossoms and I estimate that maybe only 10-15% produced fruit. During pollination, trees received a deep watering about once a week.” Here I must add that, in commercial orchards, 5-10% of apple blossoms set fruit, 2% of flowers on lemon trees set fruit, only 1% of avocado flowers set fruit and less than 10% of the flowers on most pomegranate trees set fruit so that by hand-pollinating you are definitely ahead of the game.
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