Convolvulus cneorum
Silverbush
Overview
Convolvulus cneorum is an evergreen subshrub forming a dense mound 18-30 inches (45-75 cm) tall and 24-36 inches (60-90 cm) wide. Leaves are narrow-lanceolate, 1-2.5 inches (2.5-6 cm) long and 0.2-0.4 inch (5-10 mm) wide, covered on both surfaces in dense silky hairs that lie flat and give the foliage a silver-grey cast with a metallic sheen in direct light. Funnel-shaped flowers 1-1.5 inches (2.5-4 cm) across open white with a yellow throat, from buds that are flushed pink and spirally furled. Flowering runs from May through September, with the heaviest flush in May and June and scattered flowers afterward. Stems are woody at the base, and the plant sheds its lower leaves from year 3, leaving bare stems under the canopy. Growth runs 4-8 inches (10-20 cm) per year. Plants withstand salt spray and drought once established but rot at the crown within one winter where soil holds water, and they persist 5-7 years in free-draining ground. Foliage silvering drops off under less than 6 hours of direct sun, where leaves turn grey-green and the mound opens out.
Native Range
Convolvulus cneorum grows on limestone sea cliffs, rocky coastal scrub, and stony slopes along the central Mediterranean, in Croatia, Albania, southern Italy, and Sicily. It occupies thin, sharply draining alkaline soils within reach of salt spray, from sea level to 1,600 feet (500 m). Wild populations are localised and fragmented across that range.Suggested Uses
Planted in gravel gardens, on dry banks, in raised beds, and at the front of borders in zones 8-10 at 24-30 inch (60-90 cm) spacing. Grown in coastal gardens where salt spray reaches the foliage, and in wall-top plantings with sharp drainage below the crown. Container culture uses pots of 5 gallons (19 L) or larger in a gritty mix, with the pot raised off the ground over winter, since standing water at the base kills the plant.How to Identify
Appearance
Size & Dimensions
Height1'6" - 2'6"
Width/Spread2' - 3'
Reaches mature size in approximately 3 years
Bloom Information
Flowering opens in May in zones 9-10 and in late May in zone 8, with the heaviest flush over 4-6 weeks in May and June. Scattered flowers continue through to September at 10-30% of peak numbers. An individual flower opens in the morning and closes by evening, lasting a single day. Cool overcast weather holds flowers shut, and bud production stops during spells below 55F (13C).
Detailed Descriptions
Flower Description
white with a yellow throatFoliage Description
silver-greyGrowing Conditions
Sun Requirements
Requires 6-12 hours of direct sunlight daily
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight
Care & Maintenance
Care Guide
Plants take 1 inch (25 mm) of water every 2 weeks through the first season and need no supplementary water once established, drawing on a deep root system. Winter wet on heavy or level ground rots the crown within one season, and plants are set on slopes, raised beds, or gravel with 4-6 inches (10-15 cm) of grit worked into the planting hole. Fertiliser is not applied, since rich soil produces soft green growth in place of silvered foliage and shortens plant life. Crowns are damaged at 15F (-9C) and killed near 5F (-15C), and plants in zone 8 are set against a south-facing wall. A gravel or grit mulch 1-2 inches (2.5-5 cm) deep keeps the lower stems dry, while bark and compost mulches hold moisture against the crown and cause rot. Plants decline after 5-7 years, and replacements are raised from semi-ripe cuttings taken in July and August.Pruning
Light trimming is carried out in April as growth starts, taking off no more than the outer 2-3 inches (5-8 cm) of shoot. Cuts into bare wood do not regrow, since the plant carries few dormant buds on old stems. Spent flower stems are removed at the base in September. Plants that go leggy from year 3 are replaced rather than cut back hard.Pruning Schedule
J
F
M
A
M
J
J
A
S
O
N
D
late springfall
Container Growing
✓ Suitable for container growing
Minimum container size: 5 gallons