Fertilising guide
How to fertilise Scarlet Giant Hyssop (Agastache coccinea)— schedule & NPK
Also called Scarlet Giant Hyssop, Red Giant Hyssop.
More about scarlet giant hyssop
About Scarlet Giant Hyssop
Agastache coccinea · also called Scarlet Giant Hyssop, Red Giant Hyssop · flowering
Scarlet Giant Hyssop is a striking North American perennial bearing vivid scarlet to orange tubular flower spikes from midsummer into autumn, irresistible to hummingbirds and long-tongued pollinators. More heat- and drought-tolerant than many Agastache species, it suits sunny, well-drained borders and xeriscape gardens. Often treated as a short-lived perennial or annual in cooler climates.
Growth habit: Upright, clump-forming herbaceous perennial
What fertiliser scarlet giant hyssop actually wants — and why
Scarlet Giant Hyssop flowers best on poor soil — feed it and you get a lush leafy plant with very few blooms, the exact opposite of what you want.
Little or nothing. Rich, especially nitrogen-rich, soil pushes foliage at the expense of flowers in this plant — lean ground is the technique, not a deficiency.
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 scarlet giant hyssop: 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 scarlet giant hyssop, 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 scarlet giant hyssop:
Apply a low-nitrogen, balanced fertiliser once in spring. Excess nitrogen promotes leafy growth at the expense of flowers. In poor, sandy soils, a top-dressing of compost in spring is sufficient. No supplemental feeding needed in average garden soils. In practice: no routine feeding at all for scarlet giant hyssop — at most a thin compost mulch for soil structure, never a flowering or nitrogen feed.
The dormant-season rule matters more than the exact interval: skip feeding entirely when scarlet giant hyssop 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 scarlet giant hyssop
None is the correct answer for scarlet giant hyssop. The flower-versus-foliage trade-off is the whole point: hold back and you get the display.
Feeding always goes onto already-damp soil, never dry roots — water scarlet giant hyssop first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the scarlet giant hyssop watering schedule.
Signs you are over-feeding scarlet giant hyssop
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for scarlet giant hyssop:
- Abundant leafy growth and very few flowers (the classic over-rich symptom).
- Soft, floppy stems and a sprawling, leafy habit.
- Scorched edges and salt crust if it has been fed in a container.
Signs you are under-feeding scarlet giant hyssop
- Effectively never an issue — these plants flower on poverty.
- Only on genuinely dead soil: weak, thin growth and few blooms.
- A short-lived plant in completely spent container compost.
If the symptoms point at watering, light or roots rather than nutrition, the full scarlet giant hyssop care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
If scarlet giant hyssop has accidentally been fed and is all leaf, a plain-water flush plus a move to leaner soil resets it; otherwise no flushing is needed because you are not feeding it.
Organic vs synthetic feeds for scarlet giant hyssop
Organic options
A thin compost mulch for soil structure is the absolute most; mostly, give it nothing. UK/US: leave it lean — no manure, no liquid feed. Poor soil is the active ingredient here.
Synthetic / liquid feeds
None. Synthetic feeds, particularly anything with appreciable nitrogen, directly suppress flowering in scarlet giant hyssop.
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 scarlet giant hyssop — frequently asked questions
What fertiliser does scarlet giant hyssop need?
Little or nothing. Rich, especially nitrogen-rich, soil pushes foliage at the expense of flowers in this plant — lean ground is the technique, not a deficiency. Scarlet Giant Hyssop flowers best on poor soil — feed it and you get a lush leafy plant with very few blooms, the exact opposite of what you want.
How often should I feed scarlet giant hyssop?
Apply a low-nitrogen, balanced fertiliser once in spring. Excess nitrogen promotes leafy growth at the expense of flowers. In poor, sandy soils, a top-dressing of compost in spring is sufficient. No supplemental feeding needed in average garden soils. Apply a low-nitrogen, balanced fertiliser once in spring. Excess nitrogen promotes leafy growth at the expense of flowers. In poor, sandy soils, a top-dressing of compost in spring is sufficient. No supplemental feeding needed in average garden soils. In practice: no routine feeding at all for scarlet giant hyssop — at most a thin compost mulch for soil structure, never a flowering or nitrogen feed.
What strength of feed for scarlet giant hyssop?
None is the correct answer for scarlet giant hyssop. The flower-versus-foliage trade-off is the whole point: hold back and you get the display.
What does over-feeding scarlet giant hyssop look like?
Abundant leafy growth and very few flowers (the classic over-rich symptom). Soft, floppy stems and a sprawling, leafy habit. Scorched edges and salt crust if it has been fed in a container. Feeding scarlet giant hyssop at all — especially "to help it flower" — is the defining mistake. Rich soil gives you a big green plant and almost no blooms; restraint is what produces the flowers.
Should I flush the soil of scarlet giant hyssop?
If scarlet giant hyssop has accidentally been fed and is all leaf, a plain-water flush plus a move to leaner soil resets it; otherwise no flushing is needed because you are not feeding it.
Keep reading
- Scarlet Giant Hyssop care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water scarlet giant hyssop — 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 heavy metal switch grass
- How to fertilise northwind switch grass
- How to fertilise rotstrahlbusch switch grass
- All 8452 fertilising guides in the Growli library