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Persicaria amplexicaulis 'Blackfield' (Blackfield bistort) care

Persicaria amplexicaulis 'Blackfield'

Also called Blackfield bistort, dark-flowered fleece flower.

RHS H7USDA 4-8Mildly toxic to petsIndoor 0.9-1.1 m tall and 0.9-1.2 m wide.

Watering rhythm

3-5days

Keep soil consistently moist; water every 3-5 days during dry weather

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Light

Direct sun (at least 4-6 hours)

Soil

Moisture-retentive, fertile loam or clay

Humidity

40-70%

Temp

-20 to 28°C

Pet safety

Mildly toxic to pets

Mature size

0.9-1.1 m tall and 0.9-1.2 m wide.

Care at a glance

Light

Aim for at least 4-6 hours of direct sun on the leaves. Full sun to partial shade. Full sun intensifies the dark flower colour and keeps stems upright; partial shade is tolerated where soil remains moist. If your only bright window faces south, that's perfect for persicaria amplexicaulis 'blackfield' — same window any aroid would fry on.

Watering

Watering persicaria amplexicaulis 'blackfield': keep soil consistently moist; water every 3-5 days during dry weather. The number that matters isn't the day of the week — it's how dry the top 2-3 cm of the pot feels. A finger in the soil tells you more than a watering app. After every watering, tip the saucer. Like all mountain fleece it dislikes drought. Maintain reliably damp soil for sustained flowering and lush foliage; mulch helps lock in moisture.

Soil and pot

Persicaria amplexicaulis 'Blackfield' grows best in moisture-retentive, fertile loam or clay. Happiest in damp, fertile ground, including heavy clay. Avoid free-draining, drought-prone soils unless irrigation can keep it moist. A pot with a working drainage hole is non-negotiable for this species — even free-draining mix will turn soggy in a closed planter. If you love the look of a decorative pot without a hole, use it as a cachepot around an inner nursery pot you can lift out to water.

Humidity and temperature

Persicaria amplexicaulis 'Blackfield' sits happiest at around 40-70% humidity and -20 to 28°C (-4 to 82°F). A hardy garden perennial indifferent to air humidity; ambient outdoor conditions suit it. Not a houseplant. If you keep the room above year-round and avoid placing the plant near a cold draught, a hot radiator, or an air-conditioning vent, you have already handled the two biggest indoor stressors.

Fertilising

Feed persicaria amplexicaulis 'blackfield' sparingly. Low-maintenance feeding. Mulch with compost in spring or apply a balanced fertiliser once at the start of growth; rich, moist soils rarely require more. Skip fertiliser entirely on a stressed, recently-repotted, or actively wilting plant — fertiliser salts make damage worse, not better. Wait for a round of healthy new growth before resuming a feeding rhythm.

Common problems

Below are the issues we see most often on persicaria amplexicaulis 'blackfield' in the Growli community. Each is annotated with the most common cause so you know where to start.

  • Drought stress — Foliage scorches and flowering shortens if soil dries out; consistent moisture is essential, especially in sunny sites.
  • Lax growth in shade — Too little light produces floppy stems and muted flower colour; grow in sun for compact, well-coloured spikes.
  • Congested clumps — Older clumps lose vigour and flower less freely; divide every few years to maintain performance.
  • Slug grazing — Slugs and snails target soft spring shoots; safeguard emerging growth until it toughens.

Propagation

Propagate by division in spring or autumn, as this cultivar will not come true from seed. Replant vigorous divisions promptly into moist, fertile soil. Propagation is the cheapest, most satisfying way to expand a collection — and it doubles as insurance against losing a mature plant to an accident. Take a backup cutting once the parent is established and healthy.

Toxicity to pets

Persicaria amplexicaulis 'Blackfield' is mildly toxic to pets. Persicaria amplexicaulis cultivars are not individually listed by the ASPCA Toxic and Non-Toxic Plants database, so toxicity is unconfirmed; treat with caution and verify with a vet. Ingested plant material may cause mild stomach upset in pets. If you keep cats, dogs, or curious children in the house, weigh placement carefully — a high shelf or a hanging planter is enough for casual safety. For severe ingestion incidents, call your local vet and the ASPCA Animal Poison Control Center (in the US, 888-426-4435).

Pet-safety status is sourced from the ASPCA Toxic and Non-Toxic Plant List, which catalogues the most-asked-about plants for cats, dogs, and horses.

Persicaria amplexicaulis 'Blackfield' care — frequently asked questions

What is the common name for Persicaria amplexicaulis 'Blackfield'?

Persicaria amplexicaulis 'Blackfield' is most commonly called Persicaria amplexicaulis 'Blackfield', but it is also known as Blackfield bistort, dark-flowered fleece flower. The names refer to the same species, so care instructions for Persicaria amplexicaulis 'Blackfield' apply identically to anything sold as Blackfield bistort.

How much light does persicaria amplexicaulis 'blackfield' need?

Persicaria amplexicaulis 'Blackfield' grows best in direct sun (at least 4-6 hours). Full sun to partial shade. Full sun intensifies the dark flower colour and keeps stems upright; partial shade is tolerated where soil remains moist.

How often should I water persicaria amplexicaulis 'blackfield'?

Water persicaria amplexicaulis 'blackfield' keep soil consistently moist; water every 3-5 days during dry weather. Like all mountain fleece it dislikes drought. Maintain reliably damp soil for sustained flowering and lush foliage; mulch helps lock in moisture. The finger-test (or lifting the pot to feel its weight) beats a fixed weekly calendar because pot size, light, and season all change how fast the soil dries.

Is persicaria amplexicaulis 'blackfield' toxic to cats and dogs?

Persicaria amplexicaulis 'Blackfield' is mildly toxic to pets. Persicaria amplexicaulis cultivars are not individually listed by the ASPCA Toxic and Non-Toxic Plants database, so toxicity is unconfirmed; treat with caution and verify with a vet. Ingested plant material may cause mild stomach upset in pets.

What USDA hardiness zone does persicaria amplexicaulis 'blackfield' grow in?

Persicaria amplexicaulis 'Blackfield' is rated for USDA zone 4-8 and RHS hardiness H7. Outside that range, grow it as a container plant that overwinters indoors before the first hard frost.

Persicaria amplexicaulis 'Blackfield' deep-dive guides

Every aspect of persicaria amplexicaulis 'blackfield' care, each with its own calibrated guide:

Featured in these plant shortlists

Persicaria amplexicaulis 'Blackfield' qualifies for 5 curated Growli shortlists — each one filtered objectively from our structured plant-care library, so the selection is consistent and checkable:

Related guides

Persicaria amplexicaulis 'Blackfield' is also commonly called Blackfield bistort or dark-flowered fleece flower.