Rhubarb / Pie plant (Rheum rhabarbarum) growing guide

Quick facts

Category: leafy greens
Difficulty: beginner
Days to harvest: 365 to 730 days
Harvest type: continuous production over weeks or months
Spacing: 100 cm between plants

Environment

Temperature: -30–24°C
pH: 5.5 to 6.8
EC (hydroponic): 1.4 to 2 mS/cm
Daily light: 15 to 25 mol/m²/day

Climate and zones

USDA zones: 3 to 8 (winter low around -40°C or warmer)
Frost tolerance: very hardy (survives deep cold)
Season: cool (spring and fall crops)

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

Rhubarb works in:

soil bed

Root mass is 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 (rhubarb 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	2	1	1	1
vegetative	2	1	2	1.6

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 perennial for outdoor aquaponics media beds or large containers (30 L). EC 1.5-2.5 mS/cm. pH 6.0-7.0. Temperature: cold-climate crop (USDA zones 3-8); needs winter freezing for dormancy. Full sun to partial shade (DLI 14-20 mol/m2/day). Plant divisions (pieces of crown with roots) in early spring. Do not harvest any stalks in the first year; let the plant build root reserves. In year 2, harvest lightly (a few stalks). From year 3 onward, harvest freely for 8-10 weeks in spring, then stop to let the plant store energy for next year. Pull (don't cut) stalks by grasping at the base and twisting. Each mature crown produces 2–5 kg of stalks per season. The plant is productive for 10-20+ years from a single planting. Divide crowns every 5-8 years to maintain vigor. Rhubarb is essentially pest and disease free. The dramatic foliage adds visual interest to any growing area.

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
Victoria	heirloom	730	1837 British heirloom. Green stalks with pink-red blush. Reliable, productive, the home garden standard. Less intensely colored than Crimson Red but more vigorous.
Crimson Red	open-pollinated	730	Deep red stalks. Prettier in pies, slightly less productive than Victoria. The variety with the classic 'rhubarb pie' color.
Canada Red	open-pollinated	730	Red stalks, sweet (the lowest oxalic acid of the common varieties). Late season, productive.