Fertilising guide
How to fertilise Compass Plant (Silphium laciniatum)— schedule & NPK
Also called Compass plant, Pilot weed, Rosinweed compass plant.
More about compass plant
About Compass Plant
Silphium laciniatum · also called Compass plant, Pilot weed · flowering
Silphium laciniatum is a dramatic, deep-rooted native prairie perennial of the central and eastern US, famous for its deeply pinnately-lobed basal leaves that orient north–south along a compass axis (reducing midday sun exposure), and for towering spikes of yellow daisy flowers in midsummer. The plant develops a massive taproot that can reach 4.5 m (15 ft) deep, making it extremely drought-resistant but also meaning it strongly resents transplanting once established. The most critical care fact is to site it carefully in its permanent position before planting, as moving an established plant almost always kills it. Silphium is not listed on the ASPCA toxic plant database and is not considered toxic to pets.
Growth habit: Tall, upright herbaceous perennial with a massive taproot; forms a basal rosette of large lobed leaves in early years before flowering.
What fertiliser compass plant actually wants — and why
Compass Plant 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 compass plant: 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 compass plant, 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 compass plant:
No feeding required; native to infertile prairie soils and overly fertile conditions promote excessively tall, floppy stems that may need staking. 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 compass plant 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 compass plant
Half strength is the safe default for compass plant — 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 compass plant first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the compass plant watering schedule.
Signs you are over-feeding compass plant
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for compass plant:
- 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 compass plant
- 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 compass plant care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Flush the pot of compass plant 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 compass plant
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 compass plant — frequently asked questions
What fertiliser does compass plant 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. Compass Plant 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 compass plant?
No feeding required; native to infertile prairie soils and overly fertile conditions promote excessively tall, floppy stems that may need staking. No feeding required; native to infertile prairie soils and overly fertile conditions promote excessively tall, floppy stems that may need staking. 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 compass plant?
Half strength is the safe default for compass plant — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.
What does over-feeding compass plant 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 compass plant 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 compass plant?
Flush the pot of compass plant 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
- Compass Plant care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water compass plant — 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 purple needlegrass
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- How to fertilise weeping love grass
- All 10153 fertilising guides in the Growli library