Borage (Starflower) care

Light

Most houseplants will scorch where borage thrives. Give it the windowsill you'd otherwise leave empty because everything else burned there. Full sun (6+ hours) gives the sturdiest plants and most flowers. It tolerates light shade but becomes leggy, flops, and blooms less. A plant moved abruptly from low light to direct sun bleaches in 48 hours — always acclimatise over a week.

Watering

Aim for when top 3-4 cm of soil is dry, about weekly for borage, but treat that as a starting point rather than a rule. A south-facing summer windowsill will dry the pot twice as fast as a north-facing winter room. Lift the pot; if it feels noticeably lighter than it did wet, water it. Fairly drought-tolerant once its taproot is down, but steady moisture keeps the large leaves from wilting in heat. Water at the base; wet foliage in still air invites mildew.

Soil and pot

Borage grows best in average, well-drained garden soil. Undemanding and productive even in poor, dry soil. Avoid rich or heavily fertilised ground, which produces floppy, soft growth. Good drainage is the main requirement. 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

Borage sits happiest at around Ambient outdoor humidity and 15-27°C (59-80°F). An outdoor annual unconcerned with humidity, though damp, crowded conditions encourage powdery mildew on its hairy leaves. Space plants for airflow. If you keep the room above 15 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 borage sparingly. Needs little to no feeding. Rich soil and nitrogen feeds cause weak, floppy stems. A thin compost mulch at planting is ample for a full season of bloom. 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 borage in the Growli community. Each is annotated with the most common cause so you know where to start.

• Powdery mildew — The hairy leaves are prone to white powdery mildew, especially late season in humid air. Space plants, water at the base, and remove affected lower leaves.
• Flopping and lodging — Tall, soft growth (worse in rich soil or shade) splays and breaks. Grow in lean soil and full sun, or give a light support; deadhead to keep plants tidy.
• Aggressive self-seeding — A single plant drops abundant seed and reappears everywhere. Pull spent plants before seed ripens, or harvest seed heads, to control spread.
• Black aphids on stems — Blackfly cluster on flowering tips and soft stems. Blast off with water or tolerate them, since borage's flowers draw aphid predators like hoverflies and ladybirds.

Propagation

Direct-sow seed in spring after frost where it is to grow; it has a deep taproot and dislikes transplanting. Germinates in 7-14 days. Established plants self-sow freely from dropped seed. 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

Borage is toxic to pets. ASPCA-listed as toxic to cats, dogs, and horses (Borage, Borago officinalis). Toxic principles are tannins and mucilage; reported clinical signs include vomiting, diarrhoea, and dermatitis. Borage leaves also contain pyrrolizidine alkaloids of liver concern, so keep pets from grazing it. 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.

Borage deep-dive guides

Every aspect of borage care, each with its own calibrated guide:

• Borage watering schedule
• Borage light requirements
• Best soil mix for borage
• Borage fertilizing guide
• When to repot borage
• How to propagate borage
• Borage growth rate & size
• Borage cold hardiness
• Borage temperature & humidity
• Is borage toxic to cats & dogs?
• Is borage toxic to cats?
• Is borage toxic to dogs?

Related guides

Borage is also commonly called Starflower or Bee Bush.

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• All 1284 plant care guides in the Growli library