Fertilising guide
How to fertilise Boissier's Silverbush (Convolvulus boissieri)— schedule & NPK
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.
Growth habit: Compact, cushion- or mat-forming evergreen sub-shrub.
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.
What fertiliser boissier's silverbush actually wants — and why
Boissier's Silverbush is an easy, light foliage feeder — a half-strength balanced liquid feed through the growing months keeps it green without forcing weak, sappy growth.
A balanced general houseplant feed (roughly even N-P-K) is exactly right — it is grown for foliage, so steady, moderate nitrogen for healthy leaves is the goal, not a bloom or root formula.
For the language behind the three numbers on the bottle — what nitrogen, phosphorus and potassium each do — see the NPK ratio explained entry. The short version for boissier's silverbush: match the feed to the job the plant is doing right now, not to a generic “plant food” on the shelf.
How often to feed boissier's silverbush, and which months
Feeding only earns its keep while the plant is in active growth and can use the nutrients — pour feed into a dormant or low-light plant and it simply builds up as root-burning salt. For boissier's silverbush:
Apply a very dilute, low-nitrogen fertiliser once in early spring; this plant naturally grows in impoverished soils and over-feeding causes weak, untypical growth. Treat that as sparingly through the growing season between spring through early autumn (roughly March to September); ease off in autumn and stop entirely in the low light of winter.
The dormant-season rule matters more than the exact interval: skip feeding entirely when boissier's silverbush is resting. For the wider context on indoor feeding rhythms across the seasons, the houseplant fertiliser schedule walks through the year month by month.
What strength to mix for boissier's silverbush
Half strength is the safe default for boissier's silverbush — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.
Feeding always goes onto already-damp soil, never dry roots — water boissier's silverbush first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the boissier's silverbush watering schedule.
Signs you are over-feeding boissier's silverbush
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for boissier's silverbush:
- Brown, crispy leaf tips and edges with no sign of underwatering.
- A white, crusty salt deposit on the soil surface or pot rim.
- Weak, pale, stretched new growth that flops.
- Lower leaves yellow and drop while the soil is correctly watered.
Signs you are under-feeding boissier's silverbush
- Uniformly pale or yellow-green leaves, oldest first.
- Noticeably small new leaves and stalled growth in good light and season.
- A generally tired, lacklustre look despite correct watering and light.
If the symptoms point at watering, light or roots rather than nutrition, the full boissier's silverbush care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Flush the pot of boissier's silverbush with plain water until it runs freely from the base every couple of months in the feeding season — it washes out the fertiliser salts that cause brown tips.
Organic vs synthetic feeds for boissier's silverbush
Organic options
A diluted seaweed or worm-casting feed, or fish emulsion if you can tolerate the smell indoors. UK: Westland or Baby Bio Organic, dilute seaweed; US: Espoma Indoor! or Neptune's Harvest fish & seaweed. Slow, gentle and hard to overdo.
Synthetic / liquid feeds
A general-purpose houseplant liquid at half strength — UK: Baby Bio, Westland Houseplant Feed or Phostrogen; US: Miracle-Gro Indoor Plant Food or Schultz. Convenient and fast-acting; the only risk is overdoing it.
Brand names are examples, not endorsements, and UK and US ranges differ — check the label’s own NPK and dilution rate, since formulations change.
Fertilising boissier's silverbush — frequently asked questions
What fertiliser does boissier's silverbush need?
A balanced general houseplant feed (roughly even N-P-K) is exactly right — it is grown for foliage, so steady, moderate nitrogen for healthy leaves is the goal, not a bloom or root formula. Boissier's Silverbush is an easy, light foliage feeder — a half-strength balanced liquid feed through the growing months keeps it green without forcing weak, sappy growth.
How often should I feed boissier's silverbush?
Apply a very dilute, low-nitrogen fertiliser once in early spring; this plant naturally grows in impoverished soils and over-feeding causes weak, untypical growth. Apply a very dilute, low-nitrogen fertiliser once in early spring; this plant naturally grows in impoverished soils and over-feeding causes weak, untypical growth. Treat that as sparingly through the growing season between spring through early autumn (roughly March to September); ease off in autumn and stop entirely in the low light of winter.
What strength of feed for boissier's silverbush?
Half strength is the safe default for boissier's silverbush — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.
What does over-feeding boissier's silverbush look like?
Brown, crispy leaf tips and edges with no sign of underwatering. A white, crusty salt deposit on the soil surface or pot rim. Weak, pale, stretched new growth that flops. Lower leaves yellow and drop while the soil is correctly watered. Feeding boissier's silverbush year-round on a fixed schedule, including dark winter months, is the most common mistake — it cannot use the nutrients in low light and the surplus simply burns the roots and crusts the soil.
Should I flush the soil of boissier's silverbush?
Flush the pot of boissier's silverbush with plain water until it runs freely from the base every couple of months in the feeding season — it washes out the fertiliser salts that cause brown tips.
Keep reading
- Boissier's Silverbush care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water boissier's silverbush — the watering schedule
- The houseplant fertiliser schedule — feeding through the year
- NPK ratio explained — what the three numbers on the bottle mean
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- All 10153 fertilising guides in the Growli library