Arugula Nutrient, pH & EC Guide for Hydroponics
Arugula's signature peppery bite comes from glucoerucin, which concentrates under mild drought-stress conditions - low EC and partial reservoir drawdown produces more flavour than fully fed plants.
Last updated
Arugula is a fast-growing brassica with a characteristically peppery bite derived from glucoerucin and related glucosinolates. Unlike lettuce or spinach where the goal is maximising growth rate, the best arugula is often produced under mild nutrient and water restriction that concentrates peppery compounds. Arugula also prefers lower EC overall than most greens, making it one of the more forgiving crops for beginners who tend to under-feed.
pH and EC Targets
| Stage | pH | EC (mS/cm) | PPM (approx) | Notes | |-------|-----|------------|--------------|-------| | Seedling | 6.0–7.0 | 0.5–0.8 | 250–400 | Very low starting EC; arugula is sensitive to salt stress at seedling stage | | Vegetative | 6.0–7.0 | 0.8–1.2 | 400–600 | Keep nitrogen at lower bound; excess N dilutes glucosinolate content | | Mature | 6.0–7.0 | 1.0–1.4 | 500–700 | Allow reservoir to draw down 20% between top-ups for flavour concentration |
Note on PPM: Values above use a 500 conversion factor (EC × 500 = PPM). Some meters use 700 - multiply by 1.4 to convert.
Key Nutrients
| Nutrient | Role in This Plant | Deficiency Sign | Correction | |----------|-------------------|-----------------|------------| | Sulfur | Direct precursor to glucoerucin synthesis; without adequate S, peppery character fades | Uniform young-leaf yellowing; loss of characteristic peppery aroma | Maintain SO4 at 40–60 ppm; magnesium sulfate is a convenient dual-purpose source | | Nitrogen (low) | Structural growth; deliberately kept low to avoid diluting glucosinolate content | Pale older leaves at very low N; but excess N produces bland, fast-growing plants | Target N at lower bound of standard range; use NO3 exclusively, no NH4 | | Calcium + Magnesium (3:1 ratio) | Cell-wall integrity and chlorophyll; brassica family Ca:Mg balance requirement | Tip burn (Ca), interveinal yellowing mid-leaves (Mg) | Maintain Ca 120–180 ppm and Mg 40–60 ppm for 3:1 ratio |
Deficiency Identification
- Loss of peppery flavour in otherwise healthy-looking plants: Usually caused by excess nitrogen diluting glucosinolate compounds. Reduce EC, lower N concentration, and allow mild reservoir drawdown between top-ups.
- Uniform pale yellowing on young leaves: Sulfur deficiency. Add potassium sulfate or magnesium sulfate to restore sulfur supply.
- Tip burn on outermost leaves: Salt stress from EC above 1.6. Lower EC immediately and flush with fresh solution.
- Bolting (rapid stem elongation, flowers): Temperature above 22°C or day length above 14 hours. Arugula bolts faster than most salad greens; keep cool and consider shade cloth in summer.
Feeding Schedule Notes
Arugula is one of the fastest-cycling hydroponic crops - most varieties reach harvest in 21–28 days from transplant. Start at EC 0.5–0.8 and only step up to 1.0–1.4 in the final week. Unlike most crops where frequent top-ups maintain constant EC, deliberate reservoir drawdown of 15–20% before topping up applies mild water stress that concentrates glucoerucin in leaf tissue. Do not allow roots to dry - aim for roots always submerged but reservoir level allowed to drop before refilling. Maintain solution temperature between 15–21°C; bolting accelerates above 22°C regardless of nutrient management.
Research note: Running reservoir 20% lower between top-ups (without drying roots) increases glucoerucin concentration, producing noticeably sharper flavour compared to fully fed plants.