The name "cast iron plant" refers to this plant's ability to survive in growing conditions that range from dry to moist and in lower light conditions that cause many other plants to decline. Leaves persist for several years if the plant is healthy and soil conditions and weather do not cause leaf browning. New leaves emerge in spring to midsummer and enlarge until the chill of fall halts growth. Pruning leaves in fall or winter creates a thinner looking plant.
Because cast iron plants don't grow quickly, exercise restraint in cutting away leaves. Fully brown leaves warrant complete removal. However, leaves with partial brown areas or those that are just beginning to yellow should not be removed just yet. Green parts of leaves make food for the plant, making it stronger and more able to grow more new, attractive leaves. Yellowing leaves are deteriorating, but nutrients in the leaves are being broken down and relocated to other parts of the plant. Decapitating the tops of leaves, removing just the upper dead tissues, makes the plant look butchered and awkward.
The best time to prune a cast iron plant is in spring. The plant will naturally respond with new leaves weeks later. Spring pruning allows you to evaluate the health and appearance of leaves after the winter. Cold winters can cause more dieback on leaves, especially if temperatures drop below 15 degrees Fahrenheit for several weeks. Remove fully dead leaves any time of year.
After pruning the dead leaves out of a cast iron plant, maintain good growing conditions to encourage the healthiest plants or best response of new leaf growth. Add 1/2 to 1 inch of compost atop the soil and supplement rainfall to keep the soil evenly moist, but never soggy. From spring to early fall, apply a balanced formulation of water soluble fertilizer to the plant, following product label directions for dosage. Do not over-fertilize variegated forms of cast iron plants, as this can lead to new leaves with less variegation and more plain solid green leaves instead.