Vinca major is a perennial vine with glossy, green leaves and large, funnel shaped flowers sporadically throughout the summer. Vinca minor (periwinkle) is a low-growing ground cover. It produces glossy, green leaves, as well, but the flowers are smaller and appear only in the spring. Both plants prefer partial to-full shade. Vinca annual (Catharanthus roseus) prefers sunny, hot conditions, according to Colorado State University Extension, and blooms all summer. Before implementing a fertilizer plan, understand the differences between vinca varieties.
Vincas need moderately fertile, but well-draining soils. Digging an inch of manure into the flower bed prior to planting will probably provide all the initial fertility plants need, according to Colorado State University Extension. Gardeners may top dress the soil annually with compost or manure. Annual vinca requires more frequent fertilizing than vinca minor and vinca major. Give them a monthly dose of diluted fish emulsion.
Vincas prefer a slightly acidic soil pH of 6 to 6.5. Gardeners with very alkaline soil--above 7.2--may apply an acidic fertilizer to lower the pH level of the soil. Pine needle or peat moss mulches also lower the pH level slightly. The main symptom of a pH problem in vincas is chlorosis, or yellowing of the leaves. This problem isn't caused by the soil itself, but by an iron deficiency. Alkaline soils bind iron making it unavailable for plants. The resulting deficiency causes the yellow leaves.
Fertilizer needs vary, depending on the vinca variety. Vinca minor and major require infrequent fertilizing, according to Clemson University Extension. Fertilize them annually in the spring, with a 10-10-10 balanced granular fertilizer at the rate of 6 to 8 pounds per 1,000 square feet. Vinca annual requires more frequent care. Fertilize monthly with a liquid or a balanced granular fertilizer.
Vinca annual blooms from early spring to late summer, making it a good choice for container pots. Fertilize it once a month with a liquid or granular balanced fertilizer, advises Colorado State University Extension, or mix a slow-release granular fertilizer with the potting soil before planting.
Too much fertilizer may contribute to diseases, such as gray mold, stem blight and black root rot, probably by promoting excessive lush growth, according to Clemson University. A far greater concern than fertilizing is proper watering for vincas. Vincas, especially vinca minor and vinca major, require very little if any watering, except during drought conditions. In fact, most diseases that afflict vincas are caused, in part, by watering too much or by watering incorrectly. When watering vincas, water first thing in the morning and use drip irrigation if possible to keep the leaves dry, according to Clemson University.