Soil & potting mix
Best soil for Boissier's Silverbush (Convolvulus boissieri)
Also called Boissier's silverbush, Spanish silverbush.
More about boissier's silverbush
About Boissier's Silverbush
Convolvulus boissieri · also called Boissier's silverbush, Spanish silverbush · flowering
Convolvulus boissieri (synonym C. nitidus) is a dwarf, cushion-forming evergreen sub-shrub native to rocky, sun-baked mountain slopes of southern Spain. It produces large, gleaming white to pale pink funnel-shaped flowers against dense, silver-silky foliage, making it a sought-after plant for alpine gardens, troughs, and rock gardens. It requires near-perfect drainage and full sun; it is particularly intolerant of winter wet at the root crown. It is not documented as toxic to pets.
Preferred mix: Sharply drained, gritty or stony, low-fertility soil
Watch for — Vine weevil grubs: The compact root system makes this plant particularly vulnerable to vine weevil larval feeding; inspect roots at repotting and treat with biological nematodes or imidacloprid-based drenches as permitted.
Why boissier's silverbush needs this mix
Boissier's Silverbush flowers hardest in a rich but free-draining loam — fed enough to fuel the display, open enough that the roots never waterlog.
- Flowering is expensive for boissier's silverbush: producing buds, blooms and seed draws heavily on nutrients and steady moisture, so the soil has to keep delivering all season.
- A loam-based mix holds nutrients and water far more evenly than a light peat mix, which means a longer, more reliable flowering period.
- It still needs sharp drainage — most flowering plants resent cold, wet feet far more than they resent being a little lean.
For the full picture on what makes up a good mix, see our guide to the main types of soil and potting media — it explains why each ingredient above behaves the way it does.
What goes wrong with the wrong mix
The wrong soil is one of the most common reasons boissier's silverbush struggles, and the damage often shows up weeks later as a watering problem. For this species specifically:
- A thin, hungry or sandy mix gives boissier's silverbush weak growth and few, short-lived flowers — it simply runs out of fuel.
- A heavy, badly drained soil rots the roots or crown, often over a wet winter, and you lose the plant before it ever flowers again.
- Over-rich, high-nitrogen mixes can push lush leaf at the expense of flowers — balance, not excess, is the aim.
Either starving boissier's silverbush in a thin mix or drowning it in a heavy, badly drained one. It wants the rich-but-free-draining middle, plus a flowering (higher-potassium) feed in season.
pH — does it matter for boissier's silverbush?
Most flowering plants, including boissier's silverbush, do well around pH 6.0-7.0. A cheap soil test is worth it outdoors; one notable exception is any acid-lover (such as some hydrangeas), where pH directly changes flower colour.
If you want to check or adjust it, the soil pH guide walks through testing and the safe ways to nudge a mix more acidic or more alkaline.
DIY mix vs a bagged one
A quality bagged compost works for boissier's silverbush in pots if you add grit and a flowering feed. In beds, improving the existing soil with compost and ensuring drainage beats any bag.
Drainage and the pot
Free drainage protects the roots and especially the crown over winter — raised beds, grit in the planting hole and never a waterlogged spot. Containers must have a clear drainage hole.
For perennials, refresh the top layer and feed each spring rather than disturbing the roots; for container displays, start with fresh rich mix each season. When the time comes, our repotting guide for boissier's silverbush covers the timing and technique step by step.
Boissier's Silverbush soil — frequently asked questions
What is the best soil mix for boissier's silverbush?
3 parts good loam or quality peat-free compost : 1 part well-rotted compost or leaf mould : 1 part grit or perlite. Flowering is expensive for boissier's silverbush: producing buds, blooms and seed draws heavily on nutrients and steady moisture, so the soil has to keep delivering all season.
Can I use normal potting soil for boissier's silverbush?
A thin, hungry or sandy mix gives boissier's silverbush weak growth and few, short-lived flowers — it simply runs out of fuel. A quality bagged compost works for boissier's silverbush in pots if you add grit and a flowering feed. In beds, improving the existing soil with compost and ensuring drainage beats any bag.
Does boissier's silverbush need a special pH?
Most flowering plants, including boissier's silverbush, do well around pH 6.0-7.0. A cheap soil test is worth it outdoors; one notable exception is any acid-lover (such as some hydrangeas), where pH directly changes flower colour.
Should I buy a bagged mix or make my own for boissier's silverbush?
A quality bagged compost works for boissier's silverbush in pots if you add grit and a flowering feed. In beds, improving the existing soil with compost and ensuring drainage beats any bag.
How often should I refresh the soil for boissier's silverbush?
For perennials, refresh the top layer and feed each spring rather than disturbing the roots; for container displays, start with fresh rich mix each season. Free drainage protects the roots and especially the crown over winter — raised beds, grit in the planting hole and never a waterlogged spot. Containers must have a clear drainage hole.
Keep reading
- Boissier's Silverbush care — the full brief (light, water, humidity, problems, pet safety)
- How often to water boissier's silverbush — the schedule the mix feeds into
- Repotting boissier's silverbush — when and how to refresh the mix
- Soil pH guide — test it and adjust it safely
- Should I water my plant? The simple check first
- Why is my plant wilting? Wet vs dry diagnosis
- Root rot — how the wrong soil starts it, and how to save the plant
- Best soil for thistle sage
- Best soil for chestnut-flowered sage
- Best soil for chiapas sage
- All 10153 soil and potting-mix guides in the Growli library