Rue

Quick facts

Category

herbs woody

Difficulty

intermediate

Days to harvest

90 to 120 days

Harvest type

cut leaves, plant regrows for repeated harvests

Spacing

45 cm between plants

Environment

Temperature

5–30°C

pH

6 to 8

EC (hydroponic)

1 to 1.5 mS/cm

Daily light

16 to 24 mol/m²/day

Climate and zones

USDA zones

5 to 10 (winter low around -29°C or warmer)

Frost tolerance

very hardy (survives deep cold)

Season

warm (summer crops, frost-sensitive)

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

Rue works in:

• drip / Dutch buckets
• 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 (rue 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.

Companion-growing notes

• Releases compounds through the roots that can mildly inhibit other crops in the same reservoir or bed. The effect is usually subtle but worth knowing if neighbors look stunted.

Aquaponics suitability

Not recommended for pure aquaponics. Fish waste alone doesn't provide enough of the nutrients this crop demands (typically potassium, calcium, or boron). It can be grown in a hybrid system where the reservoir is supplemented with hydroponic-style nutrients, but expect to dose actively.

Care notes

A niche herb for experienced growers interested in historical or Ethiopian cuisine. Container (10 L) with well-drained media. EC 1.0-1.5 mS/cm (very light feeder). pH 6.5-8.0 (tolerates alkaline conditions). Temperature: 15–28°C (Mediterranean; cold-hardy to zone 4). Full sun (DLI 16-22 mol/m2/day). The plant is low-maintenance once established. Harvest individual leaves sparingly (the flavor is intense; a single leaf is typically enough for a dish or drink). Handle with gloves, especially in sunny conditions, because the furanocoumarins in the sap cause painful phytophotodermatitis blisters on skin exposed to UV light. This is the same reaction caused by wild parsnip and giant hogweed. The skin reaction can be severe: avoid contact with sap, and if contact occurs, wash the area immediately and avoid sun exposure for 48 hours. Despite this hazard, rue is a valuable ornamental and historically important herb. The blue-green foliage is genuinely attractive in mixed plantings.

Further reading

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