Borage

Quick facts

Category

herbs soft

Difficulty

beginner

Days to harvest

45 to 70 days

Harvest type

cut leaves, plant regrows for repeated harvests

Spacing

45 cm between plants

Environment

Temperature

10–28°C

pH

6 to 7.5

EC (hydroponic)

1 to 1.6 mS/cm

Daily light

14 to 22 mol/m²/day

Climate and zones

USDA zones

3 to 10 (winter low around -40°C or warmer)

Frost tolerance

tolerates light frost

Season

cool (spring and fall crops)

Viable growing environments:

• outdoor year-round (in zone)
• outdoor in growing season (annual)
• unheated greenhouse / hoop house

USDA zone bounds reflect outdoor year-round survival. Anywhere outside the bounded zone range, this crop still grows as an annual in the warm months (outdoor_seasonal), under cover (greenhouse), or indoors under lights.

Growing systems

Borage works in:

• media bed (ebb and flow)
• wicking bed
• soil bed

Growing media

The substrate the roots sit in. Choice depends on the system (clay pebbles don't fit NFT channels; rockwool isn't used in media beds) and the crop (borage works in the media listed below).

Bacterial surface area matters for aquaponics: clay pebbles, lava rock, and pumice double as biofilter substrate. Low-surface media (rockwool, perlite, pea gravel) work in hydroponics but need a separate biofilter in aquaponics.

Nutrient demand by stage

NPK ratios are relative weights at each growth stage; the nutrient mix calculator scales them to absolute grams or ml. EC targets shift through the plant's life: seedlings need a much lighter solution than fruiting adults.

Aquaponics suitability

Compatible with typical aquaponics nutrient profiles. Fish waste provides enough nitrogen for healthy growth; supplemental potassium, calcium, and iron may still be needed depending on fish stocking density.

Care notes

A productive hydroponic herb grown primarily for its edible flowers. EC 1.2-2.0 mS/cm. pH 5.5-7.0. Temperature: 15–25°C (cool-season annual; heat above 28°C causes rapid bolting and reduced flower quality). Moderate to high light (DLI 14-20 mol/m2/day). Plants grow 40–80 cm tall and spread significantly; space generously. DWC or media bed systems work best because the root system is substantial. From seed to first flowers: 6-8 weeks. Each plant produces flowers continuously for 4-8 weeks before declining. The flowers are the primary harvest: pick individual flowers daily as they open, using them fresh or frozen. Frozen borage flowers in ice cubes are a popular cocktail garnish. Young leaves (before the hairs become prickly) can be added to salads or cooked like spinach. The hairy stems and older leaves are unpleasant to eat raw. Borage self-seeds aggressively in outdoor settings; in hydroponic systems, this isn't a concern. A rewarding specialty crop for growers who value edible flowers for culinary presentation or cocktail garnish.

Further reading

• Best crops for hydroponic beginners
• The Kratky method: grow lettuce with zero electricity