The leaves have been dying, and dropping off, from the bottom up, one more than the other. They stand about 2′ tall, and are in pots about 8″ wide. I feed them with liquid plant food, and they sit in a sunny window, but still they are dropping leaves.
The croton is a particularly vivid, broadleaf plant which displays a wide spectrum of red, yellow, orange and green vein and leaf (both ovate and linear) hues and patterns. Codiaeum variegatum is usually available to buy in the common varieties of C. ‘Petra’ or ‘Norma’. It is a member of the family Euphorbiaceae, native to the western Pacific Malaysia, Indonesia and Australia. As a native plant, croton is often grown as a shrub. So within this context, your plant is known to be a heavy feeder, both of nutrient-rich, richly composted soil, and daily 8-hour doses of good sunlight, and regular moisture with good drainage. This can all happen, in a mini-culture, within your plant pot, with caring vigilance.
Your plants that have reached 2′ tall, will have possibly outgrown their habitat, and likely beginning to abandon their older, lower leaves for the sake of the survival of the fittest. You can either (1) re-pot your plants with a luscious new potting medium, in larger pots, or (2) take 4″ cuttings of the newer, more herbaceous stems, and, with the help of a dunk in powdered root hormone, propagate them in new growing medium, or (3) take all the good cuttings you can, and then also re-pot the original, pruned back, mother plant, with a treat of rich, moisture retaining potting medium. Plenty of light, a rich nutrient diet, a steady 19º-25º C. air temperature, spray for humidity, and sufficient (once a week) water are called for. These horticultural experiments, even on our home turf, are interesting challenges to all gardeners. All the best with re-generating your crotons.
Thank you for calling the Toronto Master Gardeners.