Several flowering plants share the name vinca, including greater periwinkle (Vinca major), lesser periwinkle (Vinca minor) and annual vinca (Catharanthus roseus), which is not a true vinca at all. All are grown for their pinwheel-shaped flowers and glossy foliage, and all share similar needs in terms of where and when they should be planted. Their roles in the garden vary, however, with annual vinca being used as a bedding plant and greater and lesser periwinkle serving as .
Climate and Type
All three vinca varieties are perennial, although they vary in where they are perennial. Greater periwinkle grows as a perennial in U.S. Department of Agriculture plant hardiness zones 7 through 9 while lesser periwinkle is perennial in USDA zones 4 through 8. Annual vinca needs warmth to survive outdoors all year and is typically grown as an annual, although it grows as a perennial in USDA zones 10 through 11.
The three vinca varieties need warmth from the start if they are to thrive and remain disease-free in a garden. Plant them after your location's average last spring frost date, when soil and air temperatures stay reliably above 65 degrees Fahrenheit. Planting during cold weather or in chilly, damp soil increases the plants' risk for fungal diseases, which can shorten the lifespan of the plants.
One exception to spring planting is when divisions are being replanted. Autumn is the best time for dividing and replanting the spring- and summer-blooming vincas, which makes division a less-desirable means of vinca propagation in areas with cold winters.
Seeds, Cuttings and Divisions
Annual vinca and lesser periwinkle both grow from seeds as well as softwood cuttings of an existing plant's stem tips. The seeds should be started 10 to 12 weeks before the location's average last spring frost date. Sow the seeds individually in peat pots filled with sterile seed-starting mix, and use 1/4 inch of the mix to cover the seeds; then moisten the mix. Cover the pots because darkness is required for the seeds' germination. Keep the pots on a heating coil set to about 77 F. After the seeds germinate, remove the cover and put the pots in a sunny location that is at least 70 F. Wait for the seed-starting mixture to dry before watering it.
Using softwood cuttings is the best choice for starting new plants of a specific annual vinca or lesser periwinkle cultivar because the cuttings will reproduce the parent plant's favorable traits exactly. Plant the cuttings in spring or early summer.
Patented cultivars of any kind of plant, however, cannot be reproduced legally in any way.
Greater periwinkle grows best from softwood cuttings, which also should be started in spring or early summer. Both greater and lesser periwinkle also grow from divisions made by separating established plants into sections that include roots. Divisions grow best in warm climates with mild, rainy winters. Divide and transplant the sections in autumn at least one month before the first average fall frost date.
Site Selection and Preparation
All vinca varieties need full sun to perform well, although some light afternoon shade helps protect plants grown in hot, dry climates. Choose a site with fast-draining, moderately fertile soil with a pH level of 6.0 to 6.5. Till the soil to a depth of 6 inches, and work into it a 1-inch-thick layer of compost to improve the soil's structure and nutrient content.
Ensure the planting site provides enough space for each vinca plant you wish to grow. Greater periwinkle spreads 1 to 2 feet while lesser periwinkle spreads 1/2 to 1 1/2 feet. Annual vinca needs roughly 6 to 18 inches.
Planting vinca seedlings, cuttings, divisions and nursery plants is a relatively straightforward process, but the timing still matters. Plant on a cool, cloudy day so the plants have a chance to settle in without drying out too much. Space planting holes 12 to 18 inches apart if you want the vinca to cover a large area or 8 inches apart if you want the plants to cover a small section of land quickly. Make each hole wider than the roots of the plant you will place in the hole. Plant each vinca at the same soil depth at which it grew in its original pot, fill the rest of each planting hole with soil and make the site's soil level. Then water the soil deeply to settle the soil.
A 2-inch-thick layer of mulch between the plants will help conserve soil moisture and discourage weeds, which will help the vinca plants become established. Leave a 2-inch gap between the mulch and plants to reduce the risk of fungal infections.
Vinca plants need very little hands-on upkeep once established in a garden, but they benefit from routine care during their first growing season in the ground. Provide:
- One inch of water weekly if no rain falls for seven to 10 days. Soak the soil around the plants, taking care not to splash water on the leaves.
- Fertilizer in spring if necessary. Feed them a granular, 10-10-10 fertilizer at a rate of 3 to 4 pounds per 500 square feet of area. Apply the fertilizer to moist soil to prevent root burn, and then water the site deeply to distribute the fertilizer throughout the soil.