Fertilising guide
How to fertilise Rosinweed (Silphium integrifolium)— schedule & NPK
Also called Rosinweed, Entire-leaved rosinweed, Prairie rosinweed.
More about rosinweed
About Rosinweed
Silphium integrifolium · also called Rosinweed, Entire-leaved rosinweed · flowering
Silphium integrifolium is a robust native perennial of central and eastern US prairies, producing opposite or whorled rough-textured entire leaves along stout stems and a profusion of clear yellow daisy flowers from midsummer to early autumn. It is one of the more compact and garden-adaptable Silphium species, reaching a manageable 90-150 cm (3-5 ft), and has attracted research interest as a potential oilseed crop. Like other rosinweeds, it is deeply rooted and extremely drought-tolerant once established. Silphium integrifolium is not listed by the ASPCA as toxic to cats or dogs.
Growth habit: Upright, clump-forming herbaceous perennial with stout, rough-hairy stems and opposite to whorled leaves.
What fertiliser rosinweed actually wants — and why
Rosinweed 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 rosinweed: 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 rosinweed, 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 rosinweed:
Fertiliser is generally unnecessary in average garden soil; if soil is very poor, apply a balanced slow-release granular feed once in early spring at half the label rate. 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 rosinweed 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 rosinweed
Half strength is the safe default for rosinweed — 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 rosinweed first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the rosinweed watering schedule.
Signs you are over-feeding rosinweed
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for rosinweed:
- 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 rosinweed
- 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 rosinweed care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Flush the pot of rosinweed 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 rosinweed
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 rosinweed — frequently asked questions
What fertiliser does rosinweed 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. Rosinweed 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 rosinweed?
Fertiliser is generally unnecessary in average garden soil; if soil is very poor, apply a balanced slow-release granular feed once in early spring at half the label rate. Fertiliser is generally unnecessary in average garden soil; if soil is very poor, apply a balanced slow-release granular feed once in early spring at half the label rate. 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 rosinweed?
Half strength is the safe default for rosinweed — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.
What does over-feeding rosinweed 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 rosinweed 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 rosinweed?
Flush the pot of rosinweed 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
- Rosinweed care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water rosinweed — 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 tunic flower
- How to fertilise upright hedge parsley
- How to fertilise goat's-beard
- All 10153 fertilising guides in the Growli library