Surprisingly a member of the daisy family Asteraceae, the blue chalk plant (Senecio mandraliscae) looks like a scrawny, thornless cactus with multiple stems, sometimes called "blue fingers." Native to South Africa, it has finger-like or stick-like succulent leaves with a gray to pale steel blue color. In summer it produces tiny yellow tufted flowers that look like miniature dandelions. These flowers distinguish it from the closely resembling but white-flowering Senecio serpens, called blue chalk sticks. It grows in frost-free rocky garden soils in U.S. Department of Agriculture hardiness zones 10 and warmer.
As a succulent native to South Africa, blue chalk plant relishes heat and full sunshine. Place it where it receives at least eight hours of direct sunlight daily. Too little light cause weak, elongated leaves and stems of green rather than blue-gray. In hot desert areas with low humidity, provide it with some afternoon shade so it is not stunted.
To prevent root and stem rot, grow this tropical succulent in a fast-draining soil, preferably one that is sand-based with some organic matter incorporated. The soil pH may be slightly alkaline to slightly acidic, but it must not become bone-dry. Some moisture is needed to prevent stunted growth; excessive drought eventually dries the leaves and stems, killing the plant.
Though the blue chalk plant needs little watering overall, the sandy soil with organic matter needs to stay barely moist in general. In the intense light and heat of summer, it can receive an inch of water weekly, but in fall and winter, the soil must remain drier with no more than an inch of water every two to three weeks.
Do not worry of fertilizing the blue chalk plant in general. Occasional light addition of some compost to the soil surface provides just enough nutrients to keep new growth and leaves firm and colorful. Excessive fertilization causes very fast growth in summer, leading to leggy and floppy plants. Fertilize only in spring and summer, never in winter.
The blue chalk plant grows up to 18 inches tall and 24 inches wide. There will come a time that the stems flop over or you wish to rejuvenate the plant in a denser, lower mass. In very early spring, prune back stems to their lower reaches, where the stem tissue is firm and covered in a papery tan film. Do not overwater at this time. New stem buds will emerge from the area and rejuvenate the clump. Stem cuttings can be wedged back into the ground, where they will take root and become new plants. Remove leaves as needed to permit best insertion of stems into the ground or containers. Do not rejuvenate plants during the summer rainy season, which encourages stem rot. Prune off flower stems whenever you want.
Plants growing in movable patio containers or house plant pots should be moved outdoors in late spring when no danger of frost exists. Bring them back indoors well before fall frost threatens. Prune stems as needed to rejuvenate, and repot plants in spring, retaining old plants or starting new stem cuttings in the warm, damp, sandy potting soil mixture. Never overwater.