Fertilising guide
How to fertilise Stock (Matthiola incana)— schedule & NPK
Also called Stock, Brompton stock, Gillyflower, Ten-week stock, Hoary stock.
More about stock
About Stock
Matthiola incana · also called Stock, Brompton stock · flowering
Stock is a beloved cool-season annual or biennial prized for its intensely clove-scented spikes of flowers in purple, pink, white, and red — a staple of cottage gardens and the floristry trade. It thrives in full sun, well-drained alkaline soil, and cool temperatures. Heat ends flowering quickly, so it performs best in spring and autumn.
Growth habit: Erect, woody-based biennial or short-lived perennial; branched stems with grey-green woolly leaves and dense terminal flower racemes
Watch for — Club root (Plasmodiophora brassicae): Distorted, swollen roots causing wilting and stunted growth. Matthiola is susceptible as a Brassicaceae member. Improve drainage, lime to raise pH above 7.0, and rotate planting sites annually. No effective chemical cure.
What fertiliser stock actually wants — and why
Stock 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 stock: 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 stock, 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 stock:
Apply a balanced slow-release fertiliser at planting. Feed every 3–4 weeks with a liquid balanced feed during the growing season. Avoid high-nitrogen feeds in autumn for overwintering Brompton types, which can cause lush growth susceptible to frost damage. 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 stock 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 stock
Half strength is the safe default for stock — 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 stock first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the stock watering schedule.
Signs you are over-feeding stock
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for stock:
- 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 stock
- 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 stock care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Flush the pot of stock 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 stock
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 stock — frequently asked questions
What fertiliser does stock 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. Stock 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 stock?
Apply a balanced slow-release fertiliser at planting. Feed every 3–4 weeks with a liquid balanced feed during the growing season. Avoid high-nitrogen feeds in autumn for overwintering Brompton types, which can cause lush growth susceptible to frost damage. Apply a balanced slow-release fertiliser at planting. Feed every 3–4 weeks with a liquid balanced feed during the growing season. Avoid high-nitrogen feeds in autumn for overwintering Brompton types, which can cause lush growth susceptible to frost damage. 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 stock?
Half strength is the safe default for stock — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.
What does over-feeding stock 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 stock 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 stock?
Flush the pot of stock 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
- Stock care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water stock — the watering schedule
- The houseplant fertiliser schedule — feeding through the year
- NPK ratio explained — what the three numbers on the bottle mean
- How to fertilise lilium 'dizzy'
- How to fertilise allium 'purple sensation'
- How to fertilise allium 'globemaster'
- All 6887 fertilising guides in the Growli library