Periwinkle is one of those plants you reach for when you've got a shady, sloped, root-choked spot where nothing else will cooperate. Plant it in spring or early fall so the roots get a chance to settle before extreme heat or hard frost. Loosen the soil and work in some compost — it isn't fussy, but it knits in faster and stays glossier in soil that holds a little moisture without staying soggy. Space plants about a foot apart and they'll spread by trailing stems that root where they touch the ground; the most common mistake I see is planting it where it'll outcompete things you actually want, so give it a defined bed or an edge it can't easily creep past. Watch new plantings their first season for dry spells, and shear it back lightly in early spring to keep it dense rather than leggy.
Vinca minor has a long history in traditional European herbalism, where the leaves were used in astringent preparations and folk remedies for sore throats, minor bleeding, and as a tonic — it contains the alkaloid vincamine, which later drew real pharmaceutical interest for circulatory and cognitive uses. That said, this is decidedly not a culinary plant: all parts are toxic if eaten, so it has no place in the kitchen and should be kept away from curious pets and kids. Treat it as a handsome, hardworking groundcover and admire it for what it does best — covering tough ground and holding soil on a bank — rather than anything you'd harvest for the table.
Vinca Stem Blight
Dark lesions girdle stems, causing shoots to wilt and die back in patches across the mat. Leaves brown and collapse along affected stems.
Cut out and remove infected stems well below visible damage. Improve airflow by thinning, avoid overhead watering, and apply a fungicide labeled for Phomopsis if it recurs.
Periwinkle Root Rot
Plants yellow, wilt, and die in soggy areas. Roots turn brown and mushy with poor anchorage.
Improve drainage and reduce watering. Remove dead plants and surrounding soil, and replant only in well-draining sites.
Rust
Orange to brown raised pustules on the undersides of leaves, with yellow spotting on the upper surface. Heavy infections cause leaves to yellow and drop.
Remove and destroy infected leaves. Avoid overhead watering and improve air circulation. Apply a sulfur or copper-based fungicide if it spreads. Clear plant debris in fall.