How to Propagate Annual Vinca

Add seed-starter mix to a flat, leaving ¼ inch between the surface and the planter's rim. Irrigate the soil until excess water flows out of the drainage holes.

Sow the annual vinca seeds on the moist surface 10 weeks before you expect the last frost. Plant three seeds per 1 square inch, in rows.

Cover the seeds with ¼ inch seed-starter mix. Irrigate the soil with a spray bottle to prevent strong water jets from dislodging the annual vinca seeds.

Cover the flat with a piece of black plastic. The shield conserves moisture and heat while keeping the seeds in the dark environment they require for germination.

Transfer the flat to a room where you are able to maintain the temperature at 77 degrees Fahrenheit. Alternatively, place the planter on an electric propagation mat with the thermostat set to that temperature.

Check the soil moisture every day. Spray the surface with water whenever it begins to dry. Also check daily for seedlings. Remove the black plastic as soon as the first sprout appears. Germination takes one to two weeks.

Move the baby plants to bright, indirect light and keep them at 70 degrees Fahrenheit.

Irrigate the developing annual vinca plants whenever the soil becomes dry. Although vinca tolerates drought, do not withhold water to the point of wilting.

Feed 10-day-old seedlings a low-phosphorous complete fertilizer. A complete fertilizer contains nitrogen, phosphorous and potassium. Select a formula that provides nitrogen from a source other than ammonium nitrate.

Pull spindly, droopy and sickly seedlings from the flat when the plants reach 2 inches in height. Also, remove some of the healthy plants you retained to maintain each annual vinca 2 inches from another. The spacing allows for air circulation, which prevents disease.

Transplant 3-inch-tall seedlings to individual 2 ½-inch pots filled with potting soil. Water each plant until excess flows out of the drainage holes. Keep the plants under bright, indirect sunlight.

Fertilize the plants with the same formula two weeks after transplanting them to individual planters. Continue to irrigate the annual vinca whenever the soil becomes dry. Move them to their permanent location outdoors after the temperature begins to hold above 65 degrees Fahrenheit.