Burdock / Gobo (Arctium lappa) growing guide

Quick facts

Category: roots bulbs
Difficulty: intermediate
Days to harvest: 100 to 150 days
Harvest type: single harvest then replant
Spacing: 15 cm between plants

Environment

Temperature: 10–28°C
pH: 6 to 7.5
EC (hydroponic): 1.2 to 1.8 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: very hardy (survives deep cold)
Season: warm (summer crops, frost-sensitive)

Viable growing environments:

outdoor year-round (in zone)
outdoor in growing season (annual)

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

Burdock works in:

soil bed

Root mass is very heavy - thin-channel systems (NFT, vertical towers) can't hold this crop mechanically, hence the system list above.

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 (burdock works in the media listed below).

Medium	pH effect	Water retention	Bacterial surface
Soil-based mix (Potting soil)	varies by source	high	high

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.

Stage	N	P	K	EC target (mS/cm)
seedling	1	1	1	0.7
vegetative	2	1	2	1.5

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 specialty root crop requiring very deep growing medium (40 cm minimum, ideally 60 cm) to accommodate the long taproot. Standard hydroponic systems (NFT, DWC) cannot grow burdock; use deep raised beds, tall containers, or media beds filled with loose, obstacle-free substrate (perlite, vermiculite, or sand-perlite mix). Any stone or compacted layer causes the root to fork, reducing market quality. EC 1.5-2.5 mS/cm. pH 6.0-7.0. Temperature: 15–25°C. Moderate light (DLI 12-18 mol/m2/day). From seed to root harvest: 100-120 days. Harvest by loosening the medium around the root and pulling carefully; broken roots lose quality rapidly. The roots oxidize (turn brown) quickly when cut; keep cut pieces in acidulated water (water with a splash of vinegar or lemon juice) to prevent discoloration. For aquaponics growers with deep media beds, burdock is a unique crop that few other local growers produce, providing a competitive advantage at farmers' markets serving Japanese or health-food customers.

Notable varieties

A starting shortlist of cultivars worth knowing about. Not exhaustive: the seed catalogs list hundreds of named varieties. These are the ones home growers commonly choose between.

Cultivar	Type	Days	Notes
Takinogawa Long	open-pollinated	120	Japanese heirloom, the most-grown cultivar for gobo. Slender straight roots to 60-90 cm. Faster to harvestable size than the wild type, with milder flavor and less woody core. Available through most Asian seed catalogs.
Watanabe Early	open-pollinated	100	Earlier-maturing Japanese selection. Shorter roots (40-50 cm) than Takinogawa Long, which suits standard raised beds. Slightly sweeter flavor. The variety to start with if you've never grown burdock and don't have a 90 cm deep bed.